bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of antigen-induced proliferation of T cells from radiation-induced bone marrow chimeras by a monoclonal antibody directed against an Ia determinant on the antigen-presenting cell.
Authors: Longo D L , Schwartz R H
Published: May 2006

Chimeric B10.A T cells that had matured in a (B10.A X B10.Q)F1 environment acquired the ability to respond to poly(Glu56Lys35Phe9) (GL pi), an antigen to which the B10.A mouse is a nonresponder. The response of the chimeric B10.A T cells was initiated by GL phi on responder B10.Q antigen-presenting cells (APC) but not by GL phi on nonresponder B10.A APC. Similarly, chimeric B10.Q T cells that had matured in a (B10.A X B10.Q)F1 environment acquired the ability to respond to poly(Glu60Ala30Tyr10) (GAT) when the antigen was presented on responder B10.A APC, but not when GAT was presented on nonresponder B10.Q APC. No syngeneic haplotype preference was observed for either antigen. These interactions between H-2 nonidentical T cells and APC were inhibited by anti-H-2 antisera and a monoclonal anti-Ia antibody directed against the APC but not by such antibodies when they were directed against the T cell. These data suggest that, when they develop in a responder chimeric environment, genotypic nonresponder T cells become responders by acquiring receptors that allow them to recognize responder I region products on the surface of APC. Furthermore, the data demonstrate that the site of action of the blocking effects of the anti-Ia antibodies is the APC, thus providing strong evidence in support of the idea that Ia antigens on APC are the Ir gene products.
Identification of the immunogenically active components of the Sm and RNP antigens.
Authors: White P J , Gardner W D , Hoch S O
Published: May 2006

The spectrum of cellular targets in the autoimmune diseases is both large and varied and includes among the nuclear components the so-called Sm and RNP antigens associated with systemic lupus erythematosus. The use of immunoaffinity chromatography with dual specificity for the Sm and RNP antigens has allowed for their substantial purification from rabbit thymus in parallel and in quantity. In lieu of a functional assay, the use of a counterimmunoelectrophoresis assay provided a sensitive and rapid means of monitoring the distribution of the two antigens during purification and ensured the isolation of complexes containing the components required for antigenicity. The resulting purified complex consisted of nine polypeptides having molecular weights of approximately 9000 to 44,000 and two small RNAs of similar size. However, limited proteolysis of the isolated complex suggested that most of these polypeptides were not actually required for antigenic activity. Unlike Sm in crude thymus extracts, purified Sm was RNase sensitive. Thus, one of the major diagnostic criteria used to distinguish Sm and RNP antigens in crude extracts was shown to be invalid for purified material, suggesting that both antigens from rabbit thymus are actually ribonucleoprotein complexes.
A RNA.DNA hybrid that can adopt two conformations: an x-ray diffraction study of poly(rA).poly(dT) in concentrated solution or in fibers.
Authors: Zimmerman S B , Pheiffer B H
Published: May 2006

The RNA.DNA hybrid poly(rA).poly(dT) can adopt two conformations, depending upon its degree of hydration. Fibers yield a conventional A' RNA-like pattern at 79% relative humidity. In contrast, under highly solvated conditions this material yields an x-ray diffraction pattern with striking similarities to that of B DNA and clearly different from the RNA-like diffraction patterns previously obtained from fibers of other hybrids. A structural model is proposed for the solution form of the hybrid that has several similarities to models proposed for B DNA. The hybrid model accommodates the 2'-hydroxyl groups of the poly(rA) strand in intrachain hydrogen bonds to the adjacent ribose moieties.
DNA sequences similar to those around the simian virus 40 origin of replication are present in the monkey genome.
Authors: McCutchan T F , Singer M F
Published: May 2006

We report the molecular cloning of African green monkey genomic DNA segments that include regions of homology to the origin of replication of simian virus 40 (SV40). Three clearly different cloned segments 14 to 17 kilobase pairs (kb) long were isolated from a genomic library in lambda phage. We estimate that each of the three is repeated fewer than four times in the monkey genome. The SV40-like regions represent a small portion of the cloned segments, and these regions cross hybridize only weakly with one another. One of the three segments is described here in detail. Although the entire segment occurs only once or twice in the monkey genome, it contains DNA sequences (other than the SV40-like sequences) that are repeated elsewhere in the genome including in the other two cloned segments. The homology to SV40 is contained within about 300 base pairs of monkey DNA and is limited to the region around the viral replication origin. The nucleotide sequence of the SV40-like region was determined. It contains a large number of short stretches homologous to three specific noncoding domains around the SV40 origin of replication: the 27-base-pair region of dyad symmetry, the first set of (short) repeats that occur just on the late side of the origin, and, further in the late direction, the two 72-base-pair-long repeats. Although these components are grouped in the monkey DNA, as they are in SV40 DNA, their relative juxtaposition is scrambled.
The kinetic energy change on covalent bond formation
Authors: March Norman H. , Parr Robert G. , Mucci Joe F.
Published: May 2006

Stimulated by an analysis of the classical molecular orbital and valence bond descriptions of the two-electron normal covalent bond (both faulty), the argument is made that there exist good representations of the kinetic energy change Δ
T
, on nonpolar covalent bond formation in a diatomic molecule, of the form Δ
T
(
R
) = ∫
F
(R - r′)
S
(r′)dr′. Here
F
is a nonlinear response function which itself involves the overlap
S
. The kinetic change is known to satisfy the sum rule ∫
0
∞
Δ
T(R)dR
=

Z
α
Z
β

exactly; it is shown how this can be built into the treatment by the use of Fourier transform methods. Also considered is ∫
0
∞
Δ
T(R)R
2
dR
, which is an important additional property of the kinetic energy change. Representation of Δ
T(R)
as a Morse function, already known to be highly accurate, is shown to exactly conform to the proposed form.
Involvement of trypsin-like activity in binding of mouse spermatozoa to zonae pellucidae.
Authors: Saling P M
Published: May 2006

Work from a number of laboratories has shown that fertilization is blocked in the presence of protease inhibitors, although the specific site of inhibition has not been identified. The present experiments were designed to discriminate between sperm binding to zonae pellucidae as opposed to sperm penetration through zonae, so as to assess the effect of protease inhibitors on these two distinct events. Exposure of capacitated mouse spermatozoa to a variety of protease inhibitors directed against trypsin blocked sperm binding to zonae in a concentration-dependent manner. A chymotrypsin-directed inhibitor was not capable of blocking sperm binding to zonae. The trypsin inhibitors did not affect sperm penetration though zonae nor gamete membrane fusion if the sperm had established a firm association with the zona surface before addition of the inhibitors. Previous incubation of zona-intact eggs with the inhibitors did not lead to a reduction in sperm binding, indicating that the activity affected by the inhibitors is borne by spermatozoa. Interaction between spermatozoa and the zona surface appeared to be the specific locus of inhibition; sperm binding to zona-free eggs (i.e., binding to the egg plasma membrane) was unaltered by the trypsin inhibitors. These results suggest a reevaluation of the function of proteases in fertilization focusing on their role in initial sperm contact with the zona pellucida.
Mapping functional domains in the promoter region of the herpes thymidine kinase gene.
Authors: Zipser D , Lipsich L , Kwoh J
Published: May 2006

The cloned herpes simplex virus type 1 (HSV-1) thymidine kinase (TK; ATP:thymidine 5'-phosphotransferase, EC 2.7.1.21) gene can be used to transform TK- cells to a TK+ phenotype. Transformants generated in this way express TK at a basal constitutive level that is inducible to a higher level by infection with TK- herpes virus. We have studied the effect of mutations generated in vitro on both the constitutive and virus-induced expression of TK in transformants. Four Xho I linker insertions and two deletions in the 5' untranscribed region of the cloned HSV-1 TK gene were generated in vitro. A deletion that removed all but nine base pairs of the 5' untranscribed region virtually eliminated constitutive expression and completely prevented induction by herpes virus infection. Two of the insertions have particularly interesting properties. One, nine base pairs upstream from the cap site, inactivates constitutive expression without stopping induction. The other, 50 base pairs upstream from the cap site has the opposite effect (i.e., normal constitutive expression but no induction). Analysis of these results leads us to propose that the 5' untranscribed region of the HSV-1 TK gene is quite complex with several functional domains having differential roles in the constitutive and herpes-induced expression of the TK gene.
5-Azacytidine induction of mouse endogenous type C virus and suppression of DNA methylation.
Authors: Niwa O , Sugahara T
Published: May 2006

5-Azacytidine was found to induce the expression of BALB:virus-1 and BALB:virus-2 from K-BALB cells and ecotropic endogenous virus from AKR2B cells. Efficiency of the induction was high and comparable to that by 5-bromodeoxyuridine. The level of methylcytosine in newly synthesized DNA was drastically decreased when K-BALB cells were treated with 5-azacytidine. There was an inverse relationship between the level of DNA modification and the frequency of virus expression.
Most of the G1 period in hamster cells is eliminated by lengthening the S period.
Authors: Stancel G M , Prescott D M , Liskay R M
Published: May 2006

Two Chinese hamster cell lines, G1+-1 and CHO, have been grown in the presence of low concentrations of hydroxyurea to determine how a slowing DNA synthesis (i.e., a lengthening of the S period) affects the length of the G1 period. Hydroxyurea concentrations of approximately 10 microM do not alter the generation times of these cell lines but do cause increases in S with corresponding decreases in G1. In both cell lines, 10 microM hydroxyurea reduces G1 to an absolute value of 1 hr, which represents decreases of 70% (G1+-1) and 60% (CHO) from control values. Higher concentrations of hydroxyurea increase the generation times and lengths of S for both cell lines but do not reduce G1 below the minimum value of 1 hr. These observations indicate that the majority of G1 is expendable and most of G1 therefore cannot contain specific events required for the initiation of DNA synthesis. This result supports the hypothesis that G1 is a portion of the cell growth cycle but not of the chromosome cycle.
Characterization of T-cell surface proteins bound by heterologous antisera to antigen-specific T-cell products.
Authors: Cone R E , Rosenstein R W , Murray J H , Iverson G M , Ptak W , Gershon R K
Published: May 2006

Heterologous antisera specific for murine T-cell antigen-recognition molecules were prepared by immunization of rabbits with dinitrophenyl-specific murine T-cell suppressor factors that had been purified by hapten-affinity chromatography. The antisera (i) bind to antigen-specific T-cell products that differ in their antigen-recognizing specificity; (ii) absorb the specific suppressor activity in preparations containing suppressor factors; (iii) stain all Lyt2+ T cells brightly in indirect immunofluorescence examination, stain some Lyt1+ cells (with low intensity), and do not stain B cells; (iv) precipitate cell membrane proteins from T cells that bear striking structural resemblance to the antigen-specific molecules used for immunization. These results suggest that, like B cells, there is a commonality between antigen-specific effector molecules released by T cells and their membrane-associated receptors.
Hypersensitivity to N-methyl-N'-nitro-N-nitrosoguanidine in fibroblasts from patients with Huntington disease, familial dysautonomia, and other primary neuronal degenerations.
Authors: Scudiero D A , Meyer S A , Clatterbuck B E , Tarone R E , Robbins J H
Published: May 2006

Cells from patients with ataxia telangiectasia, a rare autosomal recessive disease characterized by primary neuronal degeneration, are abnormally sensitive to the DNA-damaging chemical N-methyl-N'-nitro-N-nitrosoguanidine. We have conducted experiments to determine whether more common primary neuronal degenerations also have a hypersensitivity to this radiomimetic chemical. Fibroblast strains from 13 control donors and from 13 patients with inherited primary neuronal degenerations were treated in vitro with the chemical, and the strains' sensitivity to the chemical was then determined by measuring their ability to divide and form colonies. Twelve of the 13 patient strains, including the 6 Huntington disease and the 4 familial dysautonomia strains, were abnormally sensitive. This hypersensitivity, which is believed to reflect defective repair of the chemically-induced DNA damage, might provide the basis for presymptomatic and prenatal diagnostic tests for these disorders and for elucidating their pathogenesis.
Enhanced macrophage degradation of low density lipoprotein previously incubated with cultured endothelial cells: recognition by receptors for acetylated low density lipoproteins.
Authors: Henriksen T , Mahoney E M , Steinberg D
Published: May 2006

Human low density lipoprotein (LDL) was incubated with an established line of rabbit aortic endothelial cells. Density gradient fractionation showed a time-, concentration-, and temperature-dependent increase in the average density of the LDL (from about 1.036 to as high as 1.070 g/ml). Incubation without cells or with other types of cultured cells (fibroblasts, hepatocytes, 3T3-L1 cells) caused no significant change in density. 125I-Labeled LDL (125I-LDL) recovered after incubation with endothelial cells (EC-modified LDL) was taken up and degraded 3 to 4 times more rapidly than control LDL by resident mouse peritoneal macrophages and by an established tumor line of mouse macrophages (J774 cells). Macrophage degradation of EC-modified 125I-LDL exhibited saturation kinetics (greater than 85% inhibited by excess unlabeled EC-modified LDL). Degradation was also inhibited by unlabeled acetylated LDL and, conversely, unlabeled EC-modified LDL inhibited degradation of acetylated 125I-LDL. Incubation of LDL with conditioned medium-removed from endothelial cell cultures modified neither its density nor its rate of degradation by macrophages. These studies show that endothelial cells have the potential to metabolically modify the LDL molecule, generating a form that is more rapidly degraded by macrophages and that is recognized by the macrophage receptor for acetylated LDL. This process may play a significant role in the pathogenesis of atherosclerosis.
Clones of the malaria parasite Plasmodium falciparum obtained by microscopic selection: their characterization with regard to knobs, chloroquine sensitivity, and formation of gametocytes.
Authors: Trager W , Tershakovec M , Lyandvert L , Stanley H , Lanners N , Gubert E
Published: May 2006

A culture line of Plasmodium falciparum (FCR-3/Gambia) was used to select and place in culture cells containing a single parasite. The method depends on examination of minute droplets of dilute cell suspensions with oil immersion phase-contrast microscopy. Droplets found to contain a single parasite were maintained under appropriate culture conditions until detectable numbers of parasites were present (generally by day 21). Of nine clones that grew up, seven were knobless and two were knobby. The clones differed somewhat in chloroquine sensitivity. Their 50% inhibition point under one set of conditions in vitro ranged from 0.02 to 0.06 micrograms of base per ml, compared with only 0.003 micrograms for the highly sensitive line FCR-8/West Africa. All three tested clones formed gametocytes under appropriate in vitro conditions.
Specific receptor for the opioid peptide dynorphin: structure--activity relationships.
Authors: Chavkin C , Goldstein A
Published: May 2006

The structural features responsible for the high potency and opiate receptor specificity of the opioid peptide dynorphin in the guinea pig ileum myenteric plexus were examined. Successive removal of COOH-terminal amino acids from dynorphin-(1--13) demonstrated important contributions of lysine-13, lysine-11, and arginine-7 to the potency. Removal of the NH2-terminal tyrosine abolished the biologic activity. Several other structural modifications were shown to affect potency: substitution of D-alanine for glycine-2 reduced the potencies of dynorphin-(1--13) amide, -(1--11), and -(1--10); and methyl esterification of the COOH terminus enhanced the potencies of dynorphin-(1--12), -(1--10), -(1--9), -(1--8), and -(1--7). Within the dynorphin sequence, lysine-11 and arginine-7 were found to be important for selectivity of interaction with the dynorphin receptor, which is distinguishable from the mu receptor in this tissue.
Effect of basis set on electron populations calculated by using Bader's criterion for partitioning electron density between atoms
Authors: Wiberg Kenneth B. , Wendoloski John J.
Published: May 2006

The effect of basis set on Bader's criterion for partitioning electron density between atoms is examined. The major effect is on the position of minimum electron density along the bond of interest. The 6-31G
**
basis leads to the more satisfactory results. The effect of including electron correlation was examined via the use of generalized valence bond wavefunctions. The change in the electron populations was small. The partitioning of electron density is useful in examining the way in which substituents interact with hydrocarbon groups.
Introduction of short-range restrictions in a protein-folding algorithm involving a long-range geometrical restriction and short-, medium-, and long-range interactions
Authors: Meirovitch H. , Scheraga H. A.
Published: May 2006

A protein-folding algorithm, based on short-range and geometrical long-range restrictions, is applied to bovine pancreatic trypsin inhibitor (BPTI). These restrictions are used to define a starting conformation, SI, by means of a space-filling model of the protein, whose energy is then minimized. The long-range restriction is the imposition of the native spatial geometric arrangement of the loops (SGAL) formed by the disulfide bonds. The short-range restrictions are applied as follows: the (ϕ, ψ) map of each residue is divided into six regions (corresponding to the right- and left-handed α-helical, extended, right- and left-handed bridge, and coil states) and the individual residues are placed in the states of the native structure [although
not
in conformations with the correct values of (ϕ, ψ)]. Minimization of the energy of SI leads to a structure, SF, with a root-mean-square deviation of 4.4 Å from NI, a previously energy-optimized version of the x-ray structure. SF is closer to the native structure than is the structure RF, which was obtained previously by imposing only the correct SGAL as a restriction. The energy of SF is much lower than that of RF but still larger than the energy of NF (the energy-refined x-ray structure).
Core (2'-5')oligoadenylate and the cordycepin analog: inhibitors of Epstein--Barr virus-induced transformation of human lymphocytes in the absence of interferon.
Authors: Doetsch P W , Suhadolnik R J , Sawada Y , Mosca J D , Flick M B , Reichenbach N L , Dang A Q , Wu J M , Charubala R , Pfleiderer W , Henderson E E
Published: May 2006

The 3'-deoxyadenosine (cordycepin) analog of (2'-5')oligo(A) [(2'-5')oligoadenylate with a triphosphate at the 5' end], synthesized enzymatically from cordycepin 5'-triphosphate in lysed rabbit reticulocytes or L-cell extracts was (i) inhibitory to translation in lysed rabbit reticulocytes and (ii) metabolically stable in extracts of either L cells or C85-5C lymphoblasts. The 5' dephosphorylated (core) (2'-5')oligo(A) and the core cordycepin analog can replace human fibroblast interferon in preventing the transformation of human lymphocytes after infection with Epstein--Barr virus B95-8 (EBV) as determined by the decreased incorporation of [3H]thymidine into cellular DNA and the inhibition of morphological transformation of EBV-infected lymphocytes. Whereas the naturally occurring core (2'-5')oligo(A) was cytotoxic to uninfected lymphocytes and proliferating lymphoblasts, the core cordycepin analog was not. Human leukocyte interferon was more effective than human fibroblast interferon in the inhibition of EBV-induced transformation of human umbilical cord lymphocytes and adult peripheral blood lymphocytes.
Deoxynucleoside [1-thio]triphosphates prevent proofreading during in vitro DNA synthesis.
Authors: Kunkel T A , Eckstein F , Mildvan A S , Koplitz R M , Loeb L A
Published: May 2006

The contribution of proofreading to the fidelity of catalysis by DNA polymerases has been determined with deoxyribonucleoside [1-thio]triphosphate substrates. These analogues, which contain a sulfur in place of an oxygen on the alpha phosphorus, are incorporated into DNA by DNA polymerases at rates similar to those of the corresponding unmodified deoxynucleoside triphosphates. The fidelity of DNA synthesis was measured with phi X174 am3 DNA; reversion to wild type occurs most frequently by a single base substitution, a C for a T at position 587. By using avian myeloblastosis virus DNA polymerase and DNA polymerase beta (enzymes without a proofreading 3' leads to 5' exonucleolytic activity), substitution of deoxycytidine thiotriphosphate in the reaction mixture did not alter fidelity. In contrast, with DNA polymerases from E. coli (DNA polymerase I) and bacteriophage T4 (enzymes containing a proofreading activity), fidelity was markedly reduced with deoxycytidine [1-thio]triphosphate. DNA containing phosphorothioate nucleotides is insensitive to hydrolysis by the exonuclease associated with these prokaryotic DNA polymerases. These combined results indicate that the deoxynucleoside [1-thio]triphosphates have normal base-pairing properties; however, once misinserted by a polymerase, they are not excised by proofreading. Proofreading of a C:A mismatch at position 587 is thereby found to contribute 20-fold to the fidelity of E. coli DNA polymerase I and a greater amount to the fidelity of bacteriophage T4 DNA polymerase.
Interactions between photoexcited rhodopsin and GTP-binding protein: kinetic and stoichiometric analyses from light-scattering changes.
Authors: Kühn H , Bennett N , Michel-Villaz M , Chabre M
Published: May 2006

In rod outer segments, photoexcited rhodopsin (R*) activates a cyclic GMP phosphodiesterase through a sequence of reactions involving a GTP-binding protein. By measuring light-scattering changes above 700 nm, we have studied the kinetics and stoichiometry of the association of R* with this protein and of the dissociation of the complex upon GDP/GTP exchange. Two light-scattering signals were obtained upon photoexcitation of rhodopsin in bovine rod outer segment membranes as well as in a reconstituted system consisting of purified GTP-binding protein and washed disc membranes; both signals depended specifically on the presence of GTP-binding protein. A "binding signal" that was observed in the absence of gTP as an increase in turbidity became saturated when a number of rhodopsin molecules equal to the number of GTP-binding protein molecules present (congruent to 10% in rod outer segments) has been bleached, suggesting that the protein binds to R* in a 1:1 complex. A "dissociation signal" of opposite sign, observed in presence of GTP at greater than or equal to 1 microM, is half maximal at 0.04% bleaching and saturated at 0.5% bleaching; it is interpreted as reflecting the dissociation of GTP-binding protein-R* complexes after GDP/GTP exchange on the GTP-binding protein, one R* being able to interact sequentially with about 100 GTP-binding protein molecules. The early time course of the binding signal is faster than that of the dissociation signal, and both signals take place in the 100-msec range at 20 degrees C.
Renin, angiotensins, and angiotensin-converting enzyme in neuroblastoma cells: evidence for intracellular formation of angiotensins.
Authors: Okamura T , Clemens D L , Inagami T
Published: May 2006

The mechanism of formation of various peptide hormones in neuronal cells in the brain is not clear. The question of whether brain angiotensin II is formed by an extracellular mechanism as in the peripheral system or by an intracellular mechanism can be answered by using cloned cells in culture. We have screened several neuroblastoma cell lines of rat and mouse origin and found at least three cell lines that contain renin (EC 3.4.99.19), angiotensin-converting enzyme (dipeptidyl carboxypeptidase; peptidyldipeptide hydrolase, EC 3.4.15.1), and angiotensins I and II. This finding was interpreted to indicate that in these cells angiotensin formation takes place by an intracellular mechanism, in contrast to the extracellular mechanism well known to occur in plasma. This study also demonstrates the existence of viable and cloned cell lines that produce renin.
Differential phosphorylation of nuclear nonhistone high mobility group proteins HMG 14 and HMG 17 during the cell cycle.
Authors: Bhorjee J S
Published: May 2006

The phosphorylation of the high-mobility group (HMG) proteins at different stages of the cell cycle was studied in synchronized HeLa cells. HMG proteins were extracted and analyzed by NaDodSO4/polyacrylamide gel electrophoresis. Although the molecular weight distribution of HMGs remains unchanged, their total amounts increase by as much as 20-25% in the G1 and S phases when compared with amounts in G2. However, the most significant finding is that there is a 7-fold increase of 32P incorporation into HMG 14 in the G2 phase compared with that in G1, and a 2-fold increase of 32P incorporation into HMG 17 in early S phase relative to the incorporation in the G1 and G2 stages. In contrast, HMG 1 and HMG 2 are not phosphorylated. The clear demonstration of differential phosphorylation of HMG 14 and 17 at specific stages of the cell cycle warrants a serious consideration of their role in tissue-specific maintenance of the altered chromatin structure characteristic of potentially active or actively transcribed chromatin domains.
Organization of the diversity--joining region in rabbit immunoglobulin heavy chains as revealed by cleavage of a specific methionine residue in a100 allotype.
Authors: Tonnelle C , Cazenave P A , Brézin C , Fougereau M
Published: May 2006

Three anti-micrococcus antibodies of restricted heterogeneity have been isolated from the antisera of homozygous a100/a100 rabbits. Heavy chains contained an unusual methionine residue at position 87 that may correlate with the a100 specificity. From this position, the sequence of a stretch of 35-50 amino acid residues was determined, permitting the definition of variable (V), diversity(D), and joining (J) segments in rabbit Ig heavy chains, with their most probable boundaries. Rabbit D regions so defined appear to be highly variable, both in sequence and in length, which varies, in the heavy chains analyzed, between 6 and 11 residues. The J regions are highly homologous to the mouse J2 segment.
Alveolar subphase pH in the lungs of anesthetized rabbits.
Authors: Nielson D W , Goerke J , Clements J A
Published: May 2006

We measured the pH of the alveolar subphase fluid by puncturing the most superficial alveoli of the exposed lungs of anesthetized rabbits with H+-selective and nonselective KCl microelectrodes. In these experiments, we bathed the lung surface with paraffin oil or buffered Ringer's solutions that had a CO2 tension of 40 Torr (1 Torr = 133.3 Pa) and found an alveolar pH of 6.92 +/- 0.01 (mean +/- sEM). When the pH of the surface buffer was below 6.7 or above 7.5, alveolar pH varied with surface buffer pH. With the nonselective electrode, we did not find a significant electrical potential difference between the alveolar fluid and the pleural surface. These results are consistent with active transport of H+ (or HCO3(-) across alveolar epithelium.
Production of fibronectin by the human alveolar macrophage: mechanism for the recruitment of fibroblasts to sites of tissue injury in interstitial lung diseases.
Authors: Rennard S I , Hunninghake G W , Bitterman P B , Crystal R G
Published: May 2006

Because cells of the mononuclear phagocyte system are known to produce fibronectin and because alveolar macrophages are activated in many interstitial lung diseases, the present study was designed to evaluate a role for the alveolar macrophage as a source of the increased levels of fibronectin found in the lower respiratory tract in interstitial lung diseases and to determine if such fibronectin might contribute to the development of the fibrosis found in these disorders by being a chemoattractant for human lung fibroblasts. Production of fibronectin by human alveolar macrophages obtained by bronchoalveolar lavage and maintained in short-term culture in serum-free conditions was demonstrated; de novo synthesis was confirmed by the incorporation of [14C]proline. This fibronectin had a monomer molecular weight of 220,000 and was antigenically similar to plasma fibronectin. Macrophages from patients with idiopathic pulmonary fibrosis produced fibronectin at a rate 20 times higher than did normal macrophages; macrophages from patients with pulmonary sarcoidosis produced fibronectin at 10 times the normal rate. Macrophages from 6 of 10 patients with various other interstitial disorders produced fibronectin at rates greater than the rate of highest normal control. Human alveolar macrophage fibronectin was chemotactic for human lung fibroblasts, suggesting a functional role for this fibronectin in the derangement of the alveolar structures that is characteristic of these disorders.
An Epstein--Barr virus early protein induces cell fusion.
Authors: Bayliss G J , Wolf H
Published: May 2006

Superinfection of Raji cells with Epstein--Barr virus (EBV) leads to syncytium formation. Studies using metabolic inhibitors and amino acid analogues suggest that the fusion-inducing factor belongs to the early group of virus-specified proteins. Induction of early EBV protein synthesis in Raji cells by using various chemicals also leads to syncytium formation, indicating that the fusion process is not caused by a virion membrane protein introduced into the cells upon infection. The relevance of these findings to the association of EBV with carcinoma of the nasopharynx is discussed.
Carbonic anhydrase C in the neural retina: transition from generalized to glia-specific cell localization during embryonic development.
Authors: Linser P , Moscona A A
Published: May 2006

The developmental profile and cellular localization of carbonic anhydrase C (carbonate dehydratase; carbonate hydro-lyase, EC 4.2.1.1) in the neural retina of chicken embryos and adults were investigated by immunochemical and immunohistochemical methods. Carbonic anhydrase C is present in the retina by the 3rd day of embryonic development. In the undifferentiated retina, it is detectable in virtually all the cells; however, as cell specialization progresses, its level declines rapidly in the emerging neurons and increases in Müller glia cells. An exception is certain amacrine neurons that contain carbonic anhydrase C to about the 16th day of development. In the adult retina, the enzyme is confined exclusively to Müller cells (the only gliocytes in the retina). Their identification was confirmed by immunostaining for glutamine synthase, an established Müller cell "marker." The presence in the mature retina of both these enzymes in Müller cells indicates that retinal gliocytes combine functional features that, in the brain, are segregated in astrocytes and oligodendrocytes. In the embryonic retina, carbonic anhydrase C and glutamine synthase differ markedly in their developmental profiles, cellular distribution, and susceptibility to regulation by cortisol and by cell interactions. Such differences make these two enzymes an attractive "marker team" for studying developmental mechanisms in embryonic retina and specific functions of Müller cells.
"Warm-up" along dimensions of movement in the ontogeny of exploration in rats and other infant mammals.
Authors: Golani I , Bronchti G , Moualem D , Teitelbaum P
Published: May 2006

When some infant mammals are placed outside their nest, a sequence of exploratory behavior occurs, displaying a regular buildup and spread of activity. This "warm-up" involves repetition of movement along specific dimensions and an orderly transition from one dimension to the next, with cephalocaudal recruitment of body and limb segments. A similar principle of organization applies to neurological recovery from lateral hypothalamic akinesia.
Mutual interaction between adjacent dG . dC actinomycin binding sites and dA . dT netropsin binding sites on the self-complementary d(C-G-C-G-A-A-T-T-C-G-C-G) duplex in solution.
Authors: Patel D J , Kozlowski S A , Rice J A , Broka C , Itakura K
Published: May 2006

The Watson-Crick imino protons, the backbone phosphodiester resonances, and the antibiotic exchangeable protons have been used as markers to monitor the separate and simultaneous binding of actinomycin and netropsin to the d(C-G-C-G-A-A-T-T-C-G-C-G) self-complementary duplex in aqueous solution. We demonstrate that intercalation of actinomycin at dG(3'-5')dC sites at either end of the duplex results in a conformational perturbation at the dA . dT tetranucleotide core of the dodecanucleotide duplex. Parallel studies of the groove binding of netropsin at dA . dT sites in the interior of the duplex reveal a conformational perturbation which extends to adjacent dG . dC base pairs in the dodecanucleotide duplex. The NMR markers demonstrate that the d(C-G-C-G-A-A-T-T-C-G-C-G) duplex can accommodate actinomycin and netropsin simultaneously at adjacent dG . dC and dA . dT tetranucleotide blocks along its length with some mutual interaction between neighboring antibiotic binding sites.
Synthetic glycopeptide substrates for receptor-mediated endocytosis by macrophages.
Authors: Robbins J C , Lam M H , Tripp C S , Bugianesi R L , Ponpipom M M , Shen T Y
Published: May 2006

Mammalian macrophages contain a transport system that binds and internalizes glycoproteins with exposed mannose residues. This system and analogous systems on other types of cells require substrates to bear multiple nonreducing terminal residues of the appropriate sugar for effective uptake. Small multivalent synthetic glycopeptides with mannose residues covalently linked through a spacer arm to the alpha- and epsilon-amino groups of lysine, dilysine, and trilysine are competitive inhibitors of rat alveolar macrophage uptake of the neoglycoprotein mannosyl-bovine serum albumin with inhibition constants in the microM range. Various compounds could be covalently attached to the alpha-carboxyl group of these glycopeptides with substantial retention of inhibitory potency. This uptake system does not recognize galactose residues, and the galactosyl analog of an inhibitory mannosylpeptide did not inhibit uptake of mannosyl-bovine serum albumin. The trimannosyldilysine ligand is not only an inhibitor but also a substrate for specific uptake by macrophage, as shown with an 125I-labeled derivative. Macrophages bound 6.4 x 10(5) molecules per cell at 0 degrees C with a dissociation constant of 2 microM. At 21 degrees C the cells could internalize the labeled conjugate with an apparent Michaelis constant of 6 microM and a maximal velocity of 1.7 x 10(5) molecules per min per cel. The dissociation constant and Michaelis constant are similar to the inhibition constant of 9 microM determined at 21 degrees C for inhibition by this conjugate at mannosyl-bovine serum albumin uptake. These synthetic substrates may be useful in targeting pharmacologic agents to macrophages, and analogous compounds may target such agents to other types of cell.
Replication of linear mitochondrial DNA from Paramecium: sequence and structure of the initiation-end crosslink.
Authors: Pritchard A E , Cummings D J
Published: May 2006

Replication of the 14-micrometer linear Paramecium mitochondrial DNA is initiated by a crosslinking of the duplex strands at the initiation end of the molecule. As a consequence of the crosslink, a head-to-head dimer molecule, or palindrome, is a replicative intermediate. The central region of the dimer molecules of two species was cloned and sequenced, In the distal regions, the sequence is palindromic as expected; however, in the central region, there is a nonpalindromic sequence that is rich in A + T and contains direct tandem repeats. It is proposed that the nonpalindromic sequence constitutes the crosslink. Implications for the replication scheme are discussed. The model is unlike any other for a linear DNA.
Stoichiometry, inhibitor sensitivity, and organization of manganese associated with photosynthetic oxygen evolution
Authors: Yocum C. F. , Yerkes C. T. , Blankenship R. E. , Sharp R. R. , Babcock G. T.
Published: May 2006

Chloroplast thylakoid membranes isolated in the presence of EDTA retain high rates of O
2
evolution (≥340 μmol·h
-1
·mg chlorophyll
-1
) but contain no Mn
2+
that is detectable by electron paramagnetic resonance (EPR) at room temperature. The total Mn
2+
content of these preparations is 4.6 per 400 chlorophylls; 0.6 Mn
2+
can be released by addition of Ca
2+
, a treatment that does not affect O
2
evolution. The remaining Mn
2+
(4 per 400 chlorophylls) appears to be functionally associated with O
2
evolution activity. Inhibition by Tris, NH
2
OH, or heat will release a small fraction of Mn
2+
from these membranes (≈25% with Tris, for example). Addition of Ca
2+
further enhances Mn
2+
release so that for Tris and for NH
2
OH, 2 and 3, respectively, Mn
2+
per 400 chlorophylls are extracted from the O
2
-evolving complex. Based on the microwave power-saturation properties of the EPR signal IIf, which arises from an intermediate electron carrier in the water splitting process, it appears that one of the four Mn
2+
associated with photosystem II is uniquely sensitive to Tris. A new model is proposed for the organization and inhibitor sensitivity of manganese in the O
2
-evolving complex.
Different dissociation pathways and observation of an excited deoxy state in picosecond photolysis of oxy- and carboxymyoglobin.
Authors: Cornelius P A , Steele A W , Chernoff D A , Hochstrasser R M
Published: May 2006

Picosecond transient absorption spectra of Mb, MbCO, and MbO2 have been studied at time delays of up to 10 ns after excitation at 353 nm. Particular attention has been paid to the rapid spectral changes that occur in the Soret region during the first 50 ps in MbCO and MbO2. In MbCO both the bleaching of the Soret peak (feature I) and the appearance of new deoxy-like absorption (feature II) occur instantaneously, whereas in MbO2 feature II is delayed with respect to feature I. A short-lived (approximately 12 ps) feature near 455 nm (feature III) was much more intense in MbO2 than in MbCO and was also identified in the transient spectrum of Mb. No evidence of subnanosecond geminate recombination was found in either MbCO or MbO2. These observations are consistent with a scheme in which MbO2 photodissociates through an excited state of Mb, whereas MbCO under the same conditions produces ground state Mb directly. The results and conclusions are compared with those of previous picosecond studies on these molecules and related hemoglobin derivatives.
Rapid glucocorticoid inhibition of vasoactive intestinal peptide-induced cyclic AMP accumulation and prolactin release in rat pituitary cells in culture.
Authors: Rotsztejn W H , Dussaillant M , Nobou F , Rosselin G
Published: May 2006

Vasoactive intestinal peptide (VIP) stimulates both adenosine 3',5'-cyclic monophosphate (cAMP) accumulation and prolactin release in normal rat pituitary cells in culture. cAMP accumulation is significant (P less than 0.01) at VIP concentrations as low as 1 nM and reaches a maximum with 0.1 microM. Addition of dexamethasone as early as 15 min before VIP inhibits VIP stimulation of both cAMP production and PRL secretion. The rapid inhibition is dose-dependent: it appears at doses as low as 0.01 pM and is complete at 1 pM dexamethasone. Increasing concentrations of dexamethasone induce a noncompetitive type of inhibition, as shown by the decrease in Vmax with no change in the apparent Km for VIP. Cycloheximide (1 mM) counteracts the inhibitory effect of dexamethasone on VIP-induced cAMP production, which suggests the involvement of a rapid protein synthesis mechanism. Ru-26988, a specific glucocorticoid devoid of any mineralocorticoid activity and which does not bind to intracellular transcortin-like component, also produces an inhibition of VIP-induced cAMP accumulation. Corticosterone also inhibits VIP-induced cAMP production but at concentrations higher than those of dexamethasone. In contrast, aldosterone, progesterone, estradiol, and testosterone have no effect. These results demonstrate that, in normal rat pituitary cells in culture, glucocorticoids at physiological concentrations rapidly inhibit the cAMP production and prolactin release induced by VIP by acting through specific glucocorticoid receptors.
Activation of lymphocytes by brominated nucleoside and cyclic nucleotide analogues: implications for the "second messenger" function of cyclic GMP.
Authors: Goodman M G , Weigle W O
Published: May 2006

The purine nucleoside guanosine, when derivatized at the C-8 position to give 8-bromoguanosine (8-BrGuo), acquires the capacity to stimulate high-level lymphocyte proliferation in the presence or absence of serum. Direct comparisons were undertaken to determine whether this activity is exerted only by virtue of the structural resemblance of 8-BrGuo to 8-bromo cyclic GMP (8-BrcGMP) (a known intracellular lymphocyte mitogen). They showed that, of the brominated guanosine derivatives studied, 8-BrGuo is the primary activator because (i) it is a far more potent lymphocyte activator than 8-BrcGMP, the order of mitogenic potency being 8-BrGuo greater than 8-bromo GMP (8-BrGMP) greater than 8-BrcGMP; (ii) it acts much more rapidly than 8-BrcGMP; (iii) it is not metabolized to 8-BrcGMP or cGMP; and (iv) it does not elevate intracellular cGMP content. cGMP is not likely to be the second messenger serving to activate B cells because (i) it does not induce significant proliferation unless brominated at the C-8 position; (ii) the brominated form is much less efficient than 8-BrGuo or 8-BrGMP; (iii) 8-BrGuo and many other mitogens do not increase intracellular cGMP; (iv) many agents that increase cGMP fail to initiate lymphocyte activation; (v) certain agents that increase cGMP (i.e., 15-hydroperoxyarachidonic acid, azide) inhibit lymphocyte activation; and (vi) addition of unbrominated cGMP to cultures stimulated with 8-BrGuo actually diminished stimulation. These data (i) indicate that, by interaction with cellular components, 8-BrGuo triggers high level lymphocyte activation and (ii) cast significant doubt on the role of cGMP as an intracellular second messenger in lymphocyte proliferation.
Isolation of a pluripotent cell line from early mouse embryos cultured in medium conditioned by teratocarcinoma stem cells.
Authors: Martin G R
Published: May 2006

This report describes the establishment directly from normal preimplantation mouse embryos of a cell line that forms teratocarcinomas when injected into mice. The pluripotency of these embryonic stem cells was demonstrated conclusively by the observation that subclonal cultures, derived from isolated single cells, can differentiate into a wide variety of cell types. Such embryonic stem cells were isolated from inner cell masses of late blastocysts cultured in medium conditioned by an established teratocarcinoma stem cell line. This suggests that such conditioned medium might contain a growth factor that stimulates the proliferation or inhibits the differentiation of normal pluripotent embryonic cells, or both. This method of obtaining embryonic stem cells makes feasible the isolation of pluripotent cells lines from various types of noninbred embryo, including those carrying mutant genes. The availability of such cell lines should made possible new approaches to the study of early mammalian development.
Down syndrome fibroblasts are hyperresponsive to beta-adrenergic stimulation.
Authors: McSwigan J D , Hanson D R , Lubiniecki A , Heston L L , Sheppard J R
Published: May 2006

The hormonal response to human skin fibroblasts after exposure to beta-adrenergic agonists, prostaglandin E1 (PGE1), and cholera toxin was monitored by intracellular cyclic AMP accumulation. Down syndrome (DS; trisomy 21) cells had an approximately 10-fold greater response to beta-adrenergic agonists than did either normal diploid skin fibroblasts or other aneusomic fibroblast strains (trisomy 13, 18, and 22). The altered response in DS fibroblasts was specific for beta-adrenergic agonists, because treatment of DS or control cells with PGE1 or cholera toxin resulted in the same degree of cyclic AMP accumulation. Experiments with 3-isobutyl-1-methylxanthine, a cyclic nucleotide phosphodiesterase inhibitor, indicated that the increased response of DS fibroblasts was not primarily a function of altered cyclic AMP degradation. Monosomy 21 cells responded less than normal diploid fibroblasts to stimulation by the beta-adrenergic agonist isoproterenol. These findings suggest that genetic information on chromosome 21 participates in regulating the beta-adrenergic response of human fibroblasts.
Mouse IgA heavy chain gene sequence: implications for evolution of immunoglobulin hinge axons.
Authors: Tucker P W , Slightom J L , Blattner F R
Published: May 2006

The complete nucleotide sequence of the gene and mRNA coding for the constant (C) region of the secreted form of the BALB/c mouse IgA immunoglobulin alpha heavy (H) chain has been determined. As in other immunoglobulins, the three C region domains of the alpha protein, C alpha 1, C alpha 2, and C alpha 3 are coded in separate exons. However, the hinge region of C alpha is not coded on a separate exon as it is in other hinge-containing immunoglobulins. Instead, the alpha hinge is coded as a 5' extension of the C alpha 2 exon, and we suggest that it may have evolved by duplication leading to incorporation of an acceptor RNA splice site into the coding portion of the C alpha 2 exon. Extensions of this concept could provide an explanation for duplications in the human alpha 1 chain.
Induction of immune cytolysis: tumor-cell killing by complement is initiated by covalent complex of monoclonal antibody and stable C3/C5 convertase.
Authors: Vogel C W , Müller-Eberhard H J
Published: May 2006

The unique specificity of monoclonal antibodies (Ab) was combined with the cell-killing function of the cytolytic alternative pathway of complement. The functionally C3b-like glycoprotein of cobra venom was linked to a murine monoclonal Ab directed to a human melanoma-associated antigen by a disulfide bond, by using a heterobifunctional crosslinking reagent. The covalent monoclonal Ab-cobra venom factor (CVF) complex exhibited specific cytolytic activity in the presence of normal or C4-deficient serum. It induced killing of melanoma cells but not of LG-2 lymphoblastoid cells or P815 mastocytoma cells. The cytolytic action of the monoclonal Ab-CVF complex was selective in that it was limited to the melanoma cells when these were mixed with one of the two other cell lines. In absence of serum, the complex was noncytotoxic. Monoclonal Ab or CVF alone had no cytolytic activity with or without serum. It is concluded that CVF covalently linked to melanoma cell-bound AB forms the stable C3/C5 convertase with factors B and D of the alternative pathway, which in turn causes formation of the membrane attack complex and thereby cell death.