bluuebunny/crossref_metadata_2025 huggingface dataset:
Lecithin:cholesterol acyltransferase-mediated modification of discoidal peripheral lymph high density lipoproteins: possible mechanism of formation of cholesterol-induced high density lipoproteins (HDLc) in cholesterol-fed dogs.
Authors: Dory L , Sloop C H , Boquet L M , Hamilton R L , Roheim P S
Published: May 2006

Peripheral lymph high density lipoproteins (HDL) of the cholesterol-fed dog differ in a number of characteristics from plasma HDL of the same animal. Their high content of free cholesterol, phospholipid, apoprotein E, and apoprotein A-IV, their greater heterogeneity in size, and the presence of many discoidal particles suggest that a portion of lymph HDL is assembled within the interstitial fluid. The present experiments demonstrate that the endogenous lecithin:cholesterol acyltransferase (LCAT) activity of whole peripheral lymph of the cholesterol-fed dog is far less (less than 1%) than that found in the plasma of the same animal (0.3 nmol/hr per ml versus 40.6 nmol/hr per ml). Addition of partially purified LCAT to whole lymph induced many changes in the chemical composition of peripheral lymph lipoproteins. After incubation with LCAT, the free cholesterol and phospholipid contents of lymph HDL decreased, from 17% to 12% and from 46% to 33%, respectively, whereas cholesteryl ester content increased from 7% to 13%. These changes were accompanied by a mass transfer of apoprotein E and cholesterol to the p less than 1.05 g/ml fraction, the complete disappearance of the discoidal particles, and a decrease in size heterogeneity of lymph HDL. These results suggest that, in the cholesterol-fed dog, cholesterol efflux into the interstitial spaces may occur in the absence of significant LCAT activity. Furthermore, our studies suggest that the subsequent reaction between lymph HDL and LCAT within the vascular compartment leads to the generation of apoprotein E and cholesteryl ester-rich cholesterol-induced HDL.
Expression of catecholaminergic characteristics by primary sensory neurons in the normal adult rat in vivo.
Authors: Katz D M , Markey K A , Goldstein M , Black I B
Published: May 2006

Expression of catecholaminergic characteristics by primary sensory neurons was examined in the vagal nodose and glossopharyngeal petrosal ganglia of the normal adult rat in vivo. Catecholaminergic phenotypic expression was documented by immunocytochemical localization of tyrosine hydroxylase (TyrOHase; EC 1.14.16.2), radiochemical assay of specific TyrOHase catalytic activity, and cytochemical localization of formaldehyde-induced catecholamine fluorescence (FIF) within principal ganglion cells. The TyrOHase-containing cells exhibited morphologic features typical of primary sensory neurons, such as an initial axon glomerulus and a single, bifurcating neurite process. These cells were distinguished from TyrOHase- and FIF-positive small intensely fluorescent cells by size, morphology, and staining intensity. TyrOHase-containing neurons appeared to be insensitive to neonatal treatment with 6-hydroxydopamine, thereby distinguishing them from sympathetic neurons. Nodose and petrosal ganglia of adult rats exhibited TyrOHase catalytic activity, linear with respect to tissue concentration over a 10-fold range, indicating that the immunoreactive enzyme was functional. Transection of specific ganglionic nerve roots depleted TyrOHase catalytic activity and neuronal immunoreactivity within the petrosal ganglion, suggesting that target organ innervation regulates enzyme levels within ganglion perikarya. Our study indicates that primary sensory neurons express catecholaminergic transmitter traits in the normal adult rat. Consequently, in the periphery, catecholaminergic characters are not restricted to the sympathoadrenal axis but are expressed by functionally and embryologically diverse populations of autonomic neurons.
Complete covalent structure of a human immunoglobulin D: sequence of the lambda light chain.
Authors: Takahashi Y , Takahashi N , Tetaert D , Putnam F W
Published: May 2006

We have determined the amino acid sequence of the lambda light chain of human IgD WAH. Together with the sequence of the delta heavy chain already reported, this establishes the complete covalent structure of a human immunoglobulin D. The sequence determination was greatly aided by our ability to use high-pressure liquid chromatography to purify large peptides, including one large fragment extending from Ser-81 through the carboxyl terminus. The IgD molecule is a four-chain monomer of Mr approximately equal to 176,000; it consists of two lambda chains (each of 214 residues, Mr = 22,893) and two delta chains (each of 512 residues, Mr approximately equal to 65,000, including carbohydrate), and, unlike murine IgD, it contains two C delta 2 domains. A computer-assisted search using the J (joining) segment of the WAH lambda chain as a test piece showed a close evolutionary relationship of human and mouse J lambda regions and suggested that germ-line J lambda genes in the two species are very similar if not identical. DNA segments encoding J lambda, J kappa, and JH appear to have had a common evolutionary origin, and, surprisingly, JH seems closer to J lambda than does J kappa.
Nitrogen photoreduction on desert sands under sterile conditions
Authors: Schrauzer Gerhard N. , Strampach Norman , Hui Liu Nan , Palmer Miles R. , Salehi Jahanshah
Published: May 2006

Sands from various geographic locations reduce N
2
from the air to NH
3
and traces of N
2
H
4
on exposure to sunlight. This N
2
photofixation occurs under sterile conditions on the surface of finely dispersed titanium minerals such as rutile, utilizing reducing equivalents generated through the photolysis of chemisorbed H
2
O. Abiological N
2
photofixation is suggested to be part of the nitrogen cycle in arid and semiarid regions. It is estimated that about 10 × 10
5
tons of N
2
is photoreduced on the total surface of the earth's deserts per year.
Cell adhesion mediated by a purified fucosyltransferase.
Authors: Rauvala H , Prieels J P , Finne J
Published: May 2006

Human embryonic skin fibroblasts attach and spread on surfaces on which a fucosyltransferase purified from human milk has been immobilized. The adhesion-enhancing effect of the transferase involves specific interactions of the enzyme surface with the cell surface carbohydrate acceptors, as suggested by the following findings. About 80% of human embryonic skin fibroblasts attach and spread in 1 hr on fucosyltransferase surfaces; in contrast, bovine serum albumin, fetuin, asialofetuin, and asialotransferrin surfaces fail to enhance adhesion. The adhesion-mediating activity of the transferase is destroyed by alkylation of the sulfhydryl groups or by heating. The adhesion on fucosyltransferase surfaces is inhibited by glycoprotein, glycolipid, and oligosaccharide acceptors containing the sugar sequence galactosyl-(beta 1 leads to 4)-N-acetylglucosamine, in agreement with the substrate specificity of the enzyme. The results suggest that glycosyltransferases are able to stimulate cell adhesion in a manner similar to that proposed for lectins.
Sequential mutations in hemagglutinins of influenza B virus isolates: definition of antigenic domains.
Authors: Krystal M , Young J F , Palese P , Wilson I A , Skehel J J , Wiley D C
Published: May 2006

Comparative analysis of the amino acid sequences of hemagglutinins (HAs) of influenza B/Lee/40, B/Md/59, and B/HK/73 viruses has allowed examination of the molecular basis of antigenic variation in type B viruses. As seen with influenza type A viruses, antigenic drift in influenza B viruses proceeds mostly through the accumulation of amino acid substitutions within the HA1 portion of the HA molecule. However, the rate of variation observed among the influenza B virus HAs appears to be significantly lower than the observed rate of variation among influenza A virus HAs. The overall rate of amino acid change in the HA1s of the influenza B viruses studied is 2% per 10 years, whereas the HA1s of H3 influenza A viruses vary by 9.2% per 10 years. The sequences of the influenza B HAs were also examined in relation to the three-dimensional model for the A/Aichi/2/68 HA. When the primary amino acid sequences are compared, it appears that most of the important structural features of the type A HAs--such as the sialic acid binding site, the disulfide linkages, and the stem structure of the trimer--are conserved in the influenza B virus HAs. Regions are also identified where extensive amino acid substitutions have occurred among the three antigenically distinct influenza B virus HAs. The locations of these areas in the B HA structure correspond to antigenic regions proposed for the A virus HAs. In addition, modulation of antigenic regions in B virus HAs may also occur through amino acid deletions and variation in glycosylation sites.
ts A1S9 locus in mouse L cells may encode a novobiocin binding protein that is required for DNA topoisomerase II activity.
Authors: Colwill R W , Sheinin R
Published: May 2006

Nuclear novobiocin binding proteins (NBPs) from a set of mouse L cells have been extensively purified by affinity chromatography on novobiocin-Sepharose columns. The NBPs, specifically eluted with 100 micrograms of novobiocin per ml, exhibited equivalent DNA topoisomerase activities (measured as ATP-dependent relaxation or catenation of phi X174 replicative-form I DNA substrate) when extracted from equal numbers of wild-type (WT-4) mouse L cells growing logarithmically at 34 degrees C or at 38.5 degrees C, from ts A1S9 cells similarly cultivated at the low, permissive temperature or from revertant ts+ AR cells in exponential growth at either temperature. The NBPs isolated from similar numbers of ts A1S9 cells grown to midlogarithmic phase and then incubated for 24 hr at 38.5 degrees C (the nonpermissive temperature) showed no topoisomerase II activity. Preliminary NaDodSO4/polyacrylamide gel electrophoretic analysis of enzymatically active material revealed that the NBPs of WT-4 and ts+ AR cells grown at 34 degrees C comprised three major polypeptides of 76,000, 74,000, and 30,000 daltons and a number of larger molecular mass components present in trace amounts. The NBP of ts A1S9 cells grown at the permissive temperature was similar, except that the 30,000-kilodalton polypeptide was not detected. Such enzymatically active NBPs from WT-4 and ts+ AR cells were unaffected by 100 micrograms of novobiocin per ml, whereas the analogous preparation from ts A1S9 cells was totally inhibited. On the basis of these and other considerations, it is postulated that the ts A1S9 locus of mouse L cells encodes a temperature-sensitive polypeptide that is required for normal DNA topoisomerase II activity.
Mini-F plasmid genes that couple host cell division to plasmid proliferation.
Authors: Ogura T , Hiraga S
Published: May 2006

A mechanism for stable maintenance of plasmids, besides the replication and partition mechanisms, has been found to be specified by genes of a mini-F plasmid. An oriC plasmid carrying both a mini-F segment necessary for partition [coordinates 46.4-49.4 kilobase pairs (kb) on the F map] and another segment (42.9-43.6 kb), designated ccd (coupled cell division), is more stably maintained than are oriC plasmids carrying only the partition segment; the stability is comparable to that of the parental mini-F plasmid. When replication of a plasmid carrying ccd is prevented and the plasmid copy number decreases, to as few as one per cell, host cell division is inhibited, but not increase of turbidity or chromosome replication. Appearance of plasmid-free segregants is therefore effectively prevented under such conditions. Experimental results suggest that reduction of the copy number of plasmids carrying the ccd region causes an inhibition of cell division and that the ccd region can be dissected into two functional regions; one (ccdB) inhibits cell division and the other (ccdA) releases the inhibition. The interplay of the ccdA and ccdB genes promotes stable plasmid maintenance by coupling host cell division to plasmid proliferation.
Chloroperoxidase generation of singlet Δ molecular oxygen observed directly by spectroscopy in the 1- to 1.6-μm region
Authors: Khan Ahsan U. , Gebauer Peter , Hager Lowell P.
Published: May 2006

The (0,0)
1
Δ
g
→
3
Σ
-
g
singlet molecular oxygen chemiluminescence emission from a biological reaction system, chloroperoxidase (EC 1.11.1.10) acting on hydrogen peroxide at low pH (phosphate buffer, pH 2.85) with Cl
-
as a cosubstrate, was recorded with an ultrasensitive IR spectrometer. The strong chemiluminescence emission peak observed at 1.30 μm provides clear evidence of the enzymatic generation of (excited) singlet oxygen from peroxide in this system.
Polypeptide components of human small nuclear ribonucleoproteins.
Authors: Wooley J C , Zukerberg L R , Chung S Y
Published: May 2006

Small nuclear RNA molecules (snRNAs) are associated with polypeptides in vivo, forming small nuclear ribonucleoprotein complexes (snRNPs). These snRNP complexes are targets for certain autoimmune antisera. Antisera of the type anti-Sm precipitate (and therefore define) a class including U1, U2, U4, U5, and U6 snRNAs, whereas antisera of the anti-RNP type precipitate only U1 snRNPs. We used these two types of autoimmune antisera (from patients with systemic lupus erythematosus) to study the polypeptide components in human cells. Sequential immunoprecipitation of the complexes from nuclear extracts with anti-RNP and anti-Sm antibodies, along with radioimmunoassay of protein transfers, identified four polypeptides of 14,000 (P14), 17,000 (P17), 26,000 (P26), and 27,000 (P27) daltons that are present on all members of this class, whereas a 68,000-dalton (P68) polypeptide is present only on U1 snRNPs. Based on the radioimmunoassay, three of these polypeptides, P17, P26, and P27, are also the antigens for anti-Sm antisera, whereas P68 is the antigen for anti-RNP antisera. Long-term phosphate labeling experiments show that the only detectably phosphorylated polypeptide is P68, which contains phosphoserine.
Prediction of the three-dimensional structure of the transforming region of the EJ/T24 human bladder oncogene product and its normal cellular homologue.
Authors: Pincus M R , van Renswoude J , Harford J B , Chang E H , Carty R P , Klausner R D
Published: May 2006

The three-dimensional structures of the transforming region of the product of the EJ/T24 human bladder oncogene and of the c-Ha ras-1 gene product have been calculated by using conformational energy calculations. These two genes, representing a transforming oncogene and its normal cellular homologue, encode 21,000-dalton peptides that differ by one amino acid at position 12. We therefore examined the energetically allowed conformations of the hydrophobic decapeptide surrounding this substitution site. The calculations show that the most favorable form of the c-Ha ras-1 gene product exists when glycine-12 is in a left-handed bend conformation. No other amino acid can adopt this conformation and thus the bladder oncogene peptide containing valine at position 12 has a markedly different three-dimensional structure. A simple model is proposed to account for the consequences of a position 12 mutation.
Geometry and orientation of neuronal processes in cat primary auditory cortex (AI) related to characteristic-frequency maps.
Authors: Reale R A , Brugge J F , Feng J Z
Published: May 2006

Microelectrode mapping and horseradish peroxidase oxidase histochemistry were combined to study the relationship between the characteristic-frequency representation and the intrinsic connectivity of the primary auditory cortex in the cat. Small extracellular iontophoretic injections of horseradish peroxidase within the characteristic-frequency map resulted in labeling of neuronal processes that, in the tangential plane, radiated out asymmetrically from the injection site over distances of several millimeters. The heaviest concentration of labeled fibers was along an axis parallel with the orientation of the isofrequency line within which the injection had been made. Thus, primary field neurons that have the same or a similar characteristic frequency have the potential of being preferentially interconnected.
A surface antigen expressed by a subset of neurons in the vertebrate central nervous system.
Authors: Hockfield S , McKay R D
Published: May 2006

Many hypotheses for the specificity of connections in the nervous system postulate the presence of surface chemical differences between neurons. Hybridoma technology offers a potential route to identify such surface antigenic differences between neurons. Monoclonal antibody Cat-301 was one of a panel of antibodies generated by immunizing mice with homogenized adult cat spinal cord. At the light microscopic level, Cat-301 recognizes a subset of neurons in many areas of the vertebrate central nervous system. This report shows at the ultrastructural level that Cat-301 binds to a surface antigen on neurons in the intact vertebrate central nervous system. Cat-301-positive neurons carry the antigen on cell bodies and proximal dendrites but not on axons. Using secondary antibody labeled with horseradish peroxidase, we show that antibody binding sites are present along the surfaces of neurons and extend around presynaptic profiles but are excluded from the synaptic cleft. The distribution of the Cat-301 antigen at central synapses is similar to that described for some components of the extracellular matrix of the neuromuscular junction. This study demonstrates that a specific surface antigen is found on a subset of neurons and suggests that other surface markers may be present on other subsets of mammalian central nervous system neurons. Antibodies against this antigen and other surface antigens may allow insight into the mechanisms involved in the formation and maintenance of synaptic connections in the central nervous system.
Evolution of a large population under gene conversion.
Authors: Nagylaki T
Published: May 2006

The dynamics of allelic frequencies at a single multiallelic locus under gene conversion is studied. Generations are discrete and nonoverlapping; the diploid monoecious population mates at random; selection, mutation, and random drift are negligible. Analytical and numerical investigation indicates the following. (i) If gene conversion is biased within at least one pair of alleles, then the frequency of at least one allele must become arbitrarily small. (ii) If conversion is biased within every pair of alleles, then the frequency of at most one allele can fail to become arbitrarily small. Although allelic frequencies may become repeatedly small instead of remaining small, the biological ubiquity of small random perturbations (due, e.g., to random genetic drift) guarantees the ultimate loss of at least one allele in case i and of all alleles but one in case ii. The decay of genetic variability is often sufficiently rapid to imply that biased gene conversion can be an important mechanism for the genetic divergence of isolated populations.
Myristyl amino-terminal acylation of murine retrovirus proteins: An unusual post-translational protein modification
Authors: Henderson Louis E. , Krutzsch Henry C. , Oroszlan Stephen
Published: May 2006

The primary structure of the NH
2
-terminal region of the
gag
gene encoded internal membrane-associated protein p15 has been determined for both Rauscher and Moloney murine leukemia viruses. Peptides generated by endopeptidases and purified by HPLC were subjected to semi-automated Edman degradation. Dipeptides obtained with dipeptidyl carboxypeptidase were identified by gas chromatography-mass spectrometry. The amino acid sequence of the first 16-residue segment of Rauscher p15 is identical to the sequence of Moloney p15 except for a single amino acid substitution (Gly→Asp) at position 13. Both proteins were found to have an acylated NH
2
terminus. By mass spectroscopy, myristic acid [CH
3
(CH
2
)
12
COOH] was found to be bound through an amide linkage to the NH
2
-terminal glycyl residue in both p15s. The results of liquid chromatography show that the NH
2
-terminal myristyl group greatly contributes to the strong binding of these modified proteins and peptides to hydrophobic surfaces. Because p15 is known to be derived from the NH
2
-terminal region of a precursor polyprotein Pr65

gag

by proteolytic cleavage in the assembled virus, it is suggested that myristylation
in vivo
takes place during the biosynthesis of Pr65

gag

. Preliminary data indicate that such modification of
gag
precursor polyproteins may be common to mammalian retroviruses. The role of NH
2
-terminal myristyl acylation of Pr65

gag

in virus assembly and the possibility of similar NH
2
-terminal modifications of
gag
-related fusion proteins of transforming viruses are discussed.
Interspecific cytoplasmic gene flow in the absence of nuclear gene flow: evidence from Drosophila.
Authors: Powell J R
Published: May 2006

mtDNA polymorphism has been studied by restriction endonuclease site variation in Drosophila pseudoobscura and its sibling species D. persimilis. Eight enzymes have been used to study 54 isofemale strains from areas where the two species are sympatric and D. pseudoobscura is allopatric. Where sympatric, 75-80% of the strains have mitochondrial genomes found in both species. Where allopatric, D. pseudoobscura has diverged to the point where none of the strains have mtDNA in common with D. persimilis. The most likely explanation for this observation is that where sympatric the two species hybridize frequently enough to keep their mtDNA from diverging. However, hybridization has not prevented their nuclear genomes from diverging, perhaps due to selection against nuclear gene introgression contrasted with little or no selection against mtDNA introgression. These observations suggest that nuclear and cytoplasmic genomes have different evolutionary dynamics.
Spectrally distinct cytochrome
b
-563 components in a chloroplast cytochrome
b
—
f
complex: Interaction with a hydroxyquinoline
N
-oxide
Authors: Clark Robert D. , Hind Geoffrey
Published: May 2006

The two heme equivalents of cytochrome
b
-563 in the photosynthetic cytochrome
b
—
f
complex can be distinguished by their rate of reduction with dithionite at 25°C and by their optical absorption spectra at 77 K. The cytochrome
b
component that is rapidly reduced after addition of dithionite or reduced ferredoxin possesses an α band that splits at 77 K into two peaks, at 557 and 561 nm. Prolonged incubation with reductant reveals a second, approximately equimolar cytochrome
b
component that has at 77 K an unsplit α-band maximum at 561 nm. The designations cytochrome
b
-563
H
and cytochrome
b
-563
L
, respectively, are proposed for the rapidly and more slowly reduced cytochrome
b
-563 components. Potentiometric titration establishes a midpoint potential,
E
m
, of -30 mV (electron change n ≈ 2) for cytochrome
b
-563
H
and -150 mV (
n
= 1) for cytochrome
b
-563
L
at pH 7.5. The reduction potential of these components is raised by 2-heptyl-4-hydroxyquinoline
N
-oxide, giving
E
m
values of +57 and -34 mV, respectively, with each titration slope approximating
n
= 2.
Fructose 2,6-bisphosphate and germination of fungal spores
Authors: Van Laere André , Van Schaftingen Emile , Hers Henri-Géry
Published: May 2006

Induction of germination of
Phycomyces blakesleeanus
spores by a heat shock and subsequent incubation at 25°C in a glucose- or 6-deoxyglucose-containing culture medium resulted in an intense (20-40 times the initial value) rise in the concentration of fructose 2,6-bisphosphate and hexose 6-phosphates. The increase in the concentration of fructose 2,6-bisphosphate but not that of hexose 6-phosphates was restricted to a 25-min period during which the spores acquired an irreversible capacity to germinate. Incubation of the spores in water for any period of time during this critical period resulted in a parallel decrease in their ability to form hexose phosphates and to germinate. A similar rise in hexose phosphate concentration was also observed when
P. blakesleeanus
spores were activated by incubation in the presence of acetate and also after induction of germination of other dormant (
Neurospora tetrasperma
) or nondormant (
Mucor racemosus
) fungal spores. Extracts of dormant and heat-activated
P. blakesleeanus
spores contain a fructose, 1,6-bisphosphatase that is inhibited by fructose 2,6-bisphosphate and AMP in a synergistic manner. They also contain a 6-phosphofructo-2-kinase and a fructose-2,6-bisphosphatase.
Characterization of an S antigen synthesized by several isolates of Plasmodium falciparum.
Authors: Anders R F , Brown G V , Edwards A
Published: May 2006

The S antigen of a Papua New Guinean isolate of Plasmodium falciparum was identified by immunoblotting as the dominant antigen in culture supernatants. An antigen identical in molecular weight (Mr 220,000), isoelectric point (pI 4.2), and immunoreactivity with sera from individuals exposed to malaria was expressed by four Papua New Guinean isolates and one isolate of unknown origin. The Mr 220,000 antigen was not detected in culture supernatants derived from two isolates from Thailand and one from Ghana. The Mr 220,000, pI 4.2 S antigen may characterize a subpopulation of parasites common to many isolates of P. falciparum, which is selected for by continuous culture in vitro. A variant S antigen, 30 kilodaltons larger but with similar immunoreactivity, was expressed by 1 of 26 clonal populations derived by limit-dilution culture from one of the Papua New Guinean isolates of P. falciparum. The characteristics of the S antigen, defined by immunoblotting, allowed it to be identified in two-dimensional separations of [35S]methionine-labeled parasite proteins, thus confirming the parasite origin of the antigen.
Characterization of a uterine-type oxytocin receptor in the rat hippocampus.
Authors: Mühlethaler M , Sawyer W H , Manning M M , Dreifuss J J
Published: May 2006

Extracellular recordings were obtained from a class of nonpyramidal neurones in hippocampal slices. Oxytocin applied to the bath at concentrations of 1 nM or greater excited these cells. This effect was reversibly antagonized by a synthetic structural analogue known to block the peripheral endocrine effects of oxytocin. The effect of oxytocin was mimicked by a selective oxytocic agonist and, with less potency, by vasopressin and by other structural analogues. The potencies of oxytocin, vasopressin, and of these analogues in the hippocampus correlated well with their uterotonic activities but not with their vasopressor or antidiuretic activities. The data suggest that a class of hippocampal neurones is endowed with receptors for oxytocin that are similar to those of uterine smooth muscle cells.
Engineering of site-directed antisera against vertebrate calmodulin by using synthetic peptide immunogens containing an immunoreactive site.
Authors: Van Eldik L J , Fok K F , Erickson B W , Watterson D M
Published: May 2006

Site-directed antisera against vertebrate calmodulin were elicited in rabbits by injection of a synthetic immunogen containing the pentadecapeptide Gly-Gln-Val-Asn-Tyr-Glu-Glu-Phe-Val-Gln-Met-Met-Thr-Ala-Lys-OH, which corresponds to residues 134-148 of vertebrate calmodulin. A major immunoreactive region (residues 127-144) of calmodulin is found in the COOH-terminal structural domain and an immunoreactive site for one antiserum is contained in the heptapeptide Asn-Tyr-Glu-Glu-Phe-Val-Gln-NH2, which corresponds to residues 137-143 of vertebrate calmodulin. This immunoreactive heptapeptide was conjugated to a carrier protein by adding a cysteine residue to the NH2 terminus of the peptide and coupling the Cys-heptapeptide to the carrier through the thiol group of the cysteine residue. Injection of this Cys-heptapeptide-protein conjugate into rabbits yielded antisera that react with the heptapeptide but not with native calmodulin. Thus, the immunoreactive heptapeptide that is exposed on the surface of calmodulin is immunogenic, but it is not sufficient to elicit antibodies that react with native calmodulin. However, when the Cys-pentadecapeptide corresponding to residues 134-148 and containing the immunoreactive heptapeptide sequence was conjugated to a carrier protein and injected into rabbits, antisera were elicited that react with the intact calmodulin molecule. The affinities and specificities of these antisera for calmodulin are similar to those of antisera elicited by injection of the intact protein and are sufficient for their use in radioimmunoassays. These results indicate that the successful engineering of site-directed antisera against proteins by using synthetic peptide immunogens may require an appropriate intramolecular environment that allows the peptide region to closely approximate the spatial orientation it adopts in the intact protein.
Hybrid gamma 2b-gamma 2a genes expressed in myeloma variants: evidence for homologous recombination.
Authors: Tilley S A , Eckhardt L A , Marcu K B , Birshtein B K
Published: May 2006

The expressed immunoglobulin heavy chain genes of five gamma 2b-gamma 2a hybrid chain-producing variants of the mouse myeloma MPC-11 (gamma 2b, kappa) have been characterized by genomic Southern blot analysis. Results show that a hybrid gamma 2b-gamma 2a gene was formed in each variant by recombination between the expressed gamma 2b gene of MPC-11 and a gamma 2a gene. The recombination sites are within regions of marked homology between gamma 2b and gamma 2a genes: at least three and probably four variants show gamma 2b-gamma 2a recombination within the heavy chain constant region 2 (CH2) domain, while the fifth has its recombination site between the penultimate nucleotide of CH1 and the eighth nucleotide of the hinge. An unexpected finding is that the hybrid heavy chain-producing variants fall into two subgroups based on their use of different gamma 2a gene forms in hybrid gene formation. This result leads to the speculation that either a tandem gamma 2a gene duplication was present in MPC-11 prior to variant generation or mitotic recombination between chromosomes occurred in the generation of one variant subgroup. The similarity of hybrid gene formation in MPC-11 variants to that apparently responsible for concerted evolution within multigene families and hybrid protein expression in various individuals is noted, and the possible relationship between hybrid gene formation and the heavy chain class switch is discussed.
Resonance Raman studies of nitric oxide binding to ferric and ferrous hemoproteins: detection of Fe(III)--NO stretching, Fe(III)--N--O bending, and Fe(II)--N--O bending vibrations.
Authors: Benko B , Yu N T
Published: May 2006

The nature of bonding interactions between Fe(III) and NO in the ferric nitrosyl complexes of myoglobin (Mb), hemoglobin A (HbA), and horseradish peroxidase (HRP) is investigated by Soret-excited resonance Raman spectroscopy. On the basis of 15NO and N18O isotope shifts, we clearly identified the Fe(III)--NO bond stretching frequencies at 595 cm-1 (ferric Mb X NO), 594 cm-1 (ferric HbA X NO), and 604 cm-1 (ferric HRP X NO). The Fe(III)--N--O bending vibrations are located at 573 cm-1 (ferric Mb X NO) and 574 cm-1 (ferric HRP X NO), which are very similar to the Fe(II)--C--O bending modes at 578 cm-1 in Mb X CO and HbA X CO. However, the Fe(III)--NO and Fe(II)--CO stretching frequencies differ by approximately equal to 90 cm-1, indicating a much stronger iron-axial ligand bond for the [Fe(III) + NO] system, which is isoelectronic with the [Fe(II) + CO] system and, hence, presumably also has a linear Fe(III)--N--O linkage (in the absence of distal steric effect). The unusually strong Fe(III)--NO bond may be attributed to the pi bonding involving the unpaired electron in the pi (NO) orbital. The N18O isotope shift data indicate that the widely accepted assignment of the Fe(II)--NO stretching vibration at approximately equal to 554 cm-1 in ferrous nitrosyl Mb/HbA is incorrect; instead, we assign it to the Fe(II)--N--O bending mode. The validity of the assignment of Fe(II)--O2 stretch at 567 cm-1 in oxy-HbA by Brunner [Brunner, H. (1974) Naturwissenschaften 61, 129-130] is now in doubt. Literature data are presented to suggest that it is the Fe(II)--O--O bending vibration.
A random-walk model for helix bending in B-DNA.
Authors: Dickerson R E , Kopka M L , Pjura P
Published: May 2006

The double-helical B-DNA dodecamer of sequence d(C-G-C-G-A-A-T-T-C-G-C-G) has been refined independently from x-ray crystal structure analyses in five different variants: d(C-G-C-G-A-A-T-T-C-G-C-G) at 16 K, at room temperature, and with bound cis-diamminedichloroplatinum(II), and d(C-G-C-G-A-A-T-T-brC-G-C-G) in 60% 2-methyl-2,4-pentanediol at 20 degrees C and 7 degrees C. These helices display overall axial bends of 22 degrees, 18 degrees, 17 degrees, 14 degrees, and 3 degrees, respectively, providing an opportunity to investigate the nature of the bending process in B-DNA. Bending from one base pair to the next is best described as a stochastic or random-walk process, having forward, retrograde, and sidewise individual steps, but with an overall sense of bending. Individual steps almost always involve rolling of adjacent base pairs over one another along their long axes, not a tilting or wedge displacement that lifts neighboring base pairs apart at one end. A slight preference is observed for bending the double helix in a direction that compresses the major groove rather than the minor, and this is intuitively reasonable in view of the narrowness of the minor groove and its occupation by the spine of hydration that stabilizes the B form of DNA. This model predicts that, when DNA is wound around the nucleosome core, it should not be smoothly curved but should exhibit discrete bends every five base pairs as proposed by Zhurkin et al. [Zhurkin, V.B., Lysov, Y. P. & Ivanov, V. I. (1979) Nucleic Acids Res. 6, 1081-1096)]. Sharper bends may occur at alternate positions, where the major groove faces the nucleosome core.
Phospholipid domains in bovine retinal rod outer segment disk membranes.
Authors: Albert A D , Yeagle P L
Published: May 2006

Phospholipid behavior in bovine retinal rod outer segment disk membranes and in phosphatidylcholine membranes containing the photopigment rhodopsin is explored. 31P NMR spectra of these systems show two distinguishable resonances. One resembles closely the 31P NMR resonance normally obtained from phospholipid bilayers. The other resonance is much broader. Thus, there appear to be two phospholipid head-group domains in this retinal membrane. Each environment confers different properties on the head groups. Phosphatidylcholine membranes containing the disk photopigment also show two phospholipid domains. Therefore, the environment in the retinal rod outer segment disk membranes characterized by the broad resonance may arise from the influence of the integral membrane protein rhodopsin on the membrane phospholipid bilayer.
Mechanisms of integration of de novo-synthesized polypeptides into membranes: signal-recognition particle is required for integration into microsomal membranes of calcium ATPase and of lens MP26 but not of cytochrome b5.
Authors: Anderson D J , Mostov K E , Blobel G
Published: May 2006

We have investigated the in vitro integration into dog pancreas microsomal membranes of three integral membrane proteins that were synthesized de novo in a wheat germ cell-free translation system: calcium ATPase of rabbit sarcoplasmic reticulum, MP26 of bovine lens fiber plasma membrane, and rat liver cytochrome b5. Biosynthetically these proteins show a common feature in that they are synthesized without a transient NH2-terminal signal sequence. Two of these proteins, ATPase and MP26, were shown to require the recently discovered signal-recognition particle (SRP) [Walter, P. & Blobel, G. (1982) Nature (London) 299, 691-698] for integration. By this criterion, therefore, they each contain at least one uncleaved signal sequence. Surprisingly, however, the uncleaved signal sequence(s) of these two proteins did not induce the characteristic SRP-mediated translation arrest that was previously shown for a cleaved signal sequence. Unlike ATPase and MP26, cytochrome b5 did not require SRP for integration into microsomal membrane. Thus, the distinction between an "insertion" sequence (specifying unassisted and opportunistic integration into any exposed membrane) and a "signal" sequence (directing integration into a specific membrane by a receptor-mediated mechanism) is a valid one. By assaying for SRP dependence, the two mechanisms of integration can now be experimentally distinguished.
cDNA clone for the human invariant gamma chain of class II histocompatibility antigens and its implications for the protein structure.
Authors: Claesson L , Larhammar D , Rask L , Peterson P A
Published: May 2006

The invariant gamma chain is transitorily associated with class II histocompatibility antigens during intracellular transport. We have isolated and sequenced a cDNA clone corresponding to the human gamma chain. mRNA hybridizing to the cDNA clone translated into a 33,000-dalton chain that associated specifically with class II antigen alpha and beta chains. The gamma chain consists of 216 amino acids. The two N-linked carbohydrates are attached to asparagines 114 and 120. A continuous stretch of hydrophobic and neutral amino acids occurs in positions 31-56 from the NH2 terminus. This region seems to constitute the transmembrane portion of the polypeptide chain. The positions of the carbohydrate moieties and the putative transmembrane segment indicate that the NH2 terminus of the gamma chain resides on the cytoplasmic side of the membrane. Cell-free translations in conjunction with radiochemical amino acid sequence analyses suggest that the gamma chain lacks an NH2-terminal signal sequence.
ampC beta-lactamase hyperproduction in Escherichia coli: natural ampicillin resistance generated by horizontal chromosomal DNA transfer from Shigella.
Authors: Olsson O , Bergström S , Lindberg F P , Normark S
Published: May 2006

Six ampicillin-resistant clinical isolates of Escherichia coli that hyperproduced the chromosomal ampC beta-lactamase were studied. By DNA sequence analysis, we found that five of them were identical over an entire 449-base-pair sequence and carried a novel strong ampC promoter [Olsson, O., Bergström, S. & Normark, S. (1982) EMBO J. 1, 1411-1416]. Except for one base pair this sequence was identical to that of a low beta-lactamase-producing clinical isolate of Shigella sonnei. Spontaneous one-step mutants of S. sonnei that overproduced the ampC beta-lactamase by 45-fold were characterized and found to be mutated at the single base that distinguishes S. sonnei from the five E. coli hyperproducers. The most likely explanation for this result is that chromosomal DNA was transferred in vivo from Shigella to E. coli across the species barrier.
Continuous family of finite-dimensional representations of a solvable Lie algebra arising from singularities
Authors: Yau Stephen S.-T.
Published: May 2006

A natural mapping from the set of complex analytic isolated hypersurface singularities to the set of finite dimensional Lie algebras is first defined. It is proven that the image under this natural mapping is contained in the set of solvable Lie algebras. This approach gives rise to a continuous inequivalent family of finite dimensional representations of a solvable Lie algebra.
Adiabatic compressibility of globular proteins.
Authors: Gavish B , Gratton E , Hardy C J
Published: May 2006

The adiabatic compressibility of several globular proteins has been measured by using an ultrasonic technique in the frequency range 0.5 to 10 MHz. The contributions to the measured compressibility from the protein matrix and from surface processes involving ionization of side chains and solvation effects are discussed. The internal protein compressibility is very low, indicating the existence of "dynamic domains" which are tentatively assigned to secondary structure elements.
Grass leaf silicification: Natural selection for an inducible defense against herbivores
Authors: McNaughton S. J. , Tarrants J. L.
Published: May 2006

Plants from four populations of three species of African grasses were collected from grasslands in Tanzania's Serengeti National Park that differ in the grazing intensity that they experience. Plants were grown in the laboratory in a factorial experiment in which variables were plant origin, species identification of plants, defoliation intensity, and supply of soluble silicate in the nutrient medium. All plants accumulated silica in leaf blades in the absence of soluble silicate from the nutrient medium. Plants native to the more heavily grazed grassland accumulated more silica in their leaf blades than did plants from the less heavily grazed site. Blade silica content was higher when plants were defoliated, indicating that silicification is an inducible defense against herbivores. The quantitative heterogeneity of this qualitatively homogeneous plant defense system may have contributed to the evolution of high species diversity in the grazing fauna.
Isolation of a cDNA clone for human X-linked 3-phosphoglycerate kinase by use of a mixture of synthetic oligodeoxyribonucleotides as a detection probe.
Authors: Singer-Sam J , Simmer R L , Keith D H , Shively L , Teplitz M , Itakura K , Gartler S M , Riggs A D
Published: May 2006

We have obtained a cDNA clone encoding most of human X-linked 3-phosphoglycerate kinase (PGK; ATP:3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3). Total mRNA was prepared from human adenocarcinoma-derived cell line LS174T and used for cDNA preparation. Double-stranded cDNA was inserted, after tailing with oligo(dC), into the plasmid vector pBR327 and cloned in Escherichia coli K-12. Transformants were screened by colony hybridization with a mixture of 32P-labeled oligodeoxyribonucleotides. A pool of hexadecamers complementary to all 32 possible sequences encoding amino acids 291-296 of X-linked PGK was used for the initial screen. One clone among 2,500 gave a strong positive signal. Plasmid DNA from this clone was purified and characterized by hybridization first to the hexadecamer probe mixture and then to an undecamer probe consisting of a mixture of four sequences. The cloned fragment hybridizes preferentially to DNA from human cells with five X chromosomes. DNA sequence analysis has established that the 1.2-kilobase-pair fragment encodes PGK from amino acid 121 through the COOH terminus.
The PHI (PHI-27)/corticotropin-releasing factor/enkephalin immunoreactive hypothalamic neuron: possible morphological basis for integrated control of prolactin, corticotropin, and growth hormone secretion.
Authors: Hökfelt T , Fahrenkrug J , Tatemoto K , Mutt V , Werner S , Hulting A L , Terenius L , Chang K J
Published: May 2006

By using the indirect immunofluorescence technique, one and the same neuron in the parvocellular part of the paraventricular nucleus has been shown to stain with antisera against three different peptides: PHI (PHI-27), corticotropin-releasing factor (CRF), and enkephalin. This could explain the well-known parallel increase in plasma prolactin, corticotropin, and growth hormone levels--for example, under certain types of stress--as being due to a concomitant release of PHI-like, CRF-like, and enkephalin-like peptides from the same nerve endings in the median eminence. A hypothetical mechanism for the co-ordinated release of these three anterior pituitary hormones is discussed.
Identification of two sodium channel subtypes in chick heart and brain.
Authors: Rogart R B , Regan L J , Dziekan L C , Galper J B
Published: May 2006

Na+ channels in chick brain and heart have been directly compared by measuring binding of tritium-labeled saxitoxin ([3H]STX) to the two tissues under identical conditions. Maximum saturable uptake and toxin affinity were considerably less in chick heart than in chick brain, requiring the development of an assay method to resolve specific [3H]STX uptake in heart. With this method, binding to both preparations consisted of a specific saturable component and a linear nonspecific component. The equilibrium dissociation constant for [3H]STX measured in chick heart (6.2-8.8 nM) was 20-30 times higher than that measured in chick brain (0.3 nM). The dissociation rate for [3H]STX was only about twice as fast in heart as it was in brain, indicating that the decrease in toxin affinity in heart results predominantly from a slowed toxin association rate. The decreased affinity for [3H]STX found at the chick heart Na+ channel is compared with toxin-resistant Na+ channels in other preparations. The existence of two Na+ channel subtypes is proposed, with high affinity and low affinity for saxitoxin and tetrodotoxin; the significance of this classification is discussed.
Abnormal splice in a mutant human beta-globin gene not at the site of a mutation.
Authors: Dobkin C , Pergolizzi R G , Bahre P , Bank A
Published: May 2006

We have studied the expression of a cloned mutant human beta-globin gene in tissue culture cells. The gene, which was previously isolated from the chromosomal DNA of an individual with a low level of normal beta-globin expression (beta+-thalassemia), contains five mutations inside the large intervening sequence (IVS2), as well as a silent change in codon 2. This beta-thalassemia gene (thal) was inserted into a plasmid that is replicated and transcribed in a line of monkey kidney cells in culture. S1 nuclease mapping of the beta-globin RNA transcribed from this gene indicates that some of the beta-globin RNA is spliced abnormally by using a cryptic 3' splice sequence normally present in IVS2 but not used in processing the normal beta-globin transcript. The cryptic 3' splice site is not the site of a mutation in the thal gene. Because neither the 5' or 3' splice junction nor the cryptic site is mutated in this gene, it is most likely that the mutation at position 705 of IVS2, the only nonpolymorphic change in the gene, interferes indirectly with normal processing. These results suggest that certain sequences within IVS must be conserved to prevent abnormal splicing and loss of gene function.
Quantitative spatial distributions of calcium, phosphorus, and sulfur in calcifying epiphysis by high resolution electron spectroscopic imaging.
Authors: Arsenault A L , Ottensmeyer F P
Published: May 2006

Electron spectroscopic imaging, a new technique that permits the quantitative detection of the spatial distributions of atomic elements at high resolution, has been applied to the epiphyseal zone of hypertrophy in the mouse for the visualization of calcium, phosphorus, and sulfur. Longitudinally sectioned epiphyseal growth plates reveal a developmental sequence in the longitudinal septum leading from a noncalcified matrix to a calcified matrix. During the early stages of this transition, matrix granules containing highly localized concentrations of P (200-400 atoms/nm2) are found spatially separate from Ca-containing sites. These Ca localizations displayed a concentration range of 20-350 atoms/nm2 and a complete spatial overlap with sulfur. At these sites, S levels range from 10 to 200 atoms/nm2. At a later stage, and therefore more proximal to the zone of provisional calcification, the usual scattered, irregularly shaped mineral deposits are found. These sites contain a virtual superposition of Ca with both P and S. The Ca/P and Ca/S ratios of these mineral deposits are predominantly 1.0 with only minor, locally varying ratios present.
Low molecular weight microtubule-associated proteins are light chains of microtubule-associated protein 1 (MAP 1).
Authors: Vallee R B , Davis S E
Published: May 2006

Microtubule-associated protein 1 (MAP 1; Mr = 350,000) was analyzed by column chromatography of microtubule protein obtained from calf brain gray and white matter. Two low molecular weight proteins (LMW MAPs; Mr 28,000 and 30,000) were found to cochromatograph with MAP 1 under all conditions examined. MAP 1 and the LMW MAPs were purified from calf brain white matter as a complex containing approximately equimolar amounts of the three species. Urea (6 M) was used to remove the LMW MAPs from MAP 1. Binding of MAP 1 to microtubules was unaffected by urea and occurred with or without the LMW species. Electron microscopy of microtubules composed of purified tubulin and either MAP 1 preparation revealed that, like MAP 2, MAP 1 has the appearance of a filamentous arm on the microtubule surface.