bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of cholesterol synthesis in man by isotope kinetics of squalene.
Authors: Liu G C , Ahrens E H , Schreibman P H , Samuel P , McNamara D J , Crouse J R
Published: May 2006

A method for measuring the rate of total daily cholesterol synthesis in man has been developed through isotope kinetic studies of squalene biosynthesis after intravenous administration of [14C]mevalonic acid. Plasma squalene becomes rapidly labeled, reaching maximal specific activity approximately 100 min after mevalonate administration and then decays exponentially to reach undetectable levels in 12 hr. The rate of daily squalene synthesis equals the percent dose of mevalonate converted to cholesterol divided by the area under the specific activity curve of squalene; the fraction of the dose of mevalonate converted to cholesterol is calculated by the simultaneous injection of [3H]- and [14C] cholesterol in plasma. The premise that squalene and cholesterol synthetic rates are equivalent was tested. In seven patients it was found that the mean daily cholesterol synthesis rates estimated simultaneously by sterol balance and by sqyalene kinetic methods agreed within 8%. In addition, fractional conversions of mevalonic acid to cholesterol were highly correlated with cholesterol synthesis rates. Maximum estimates of the pool sizes and half-lives of metabolically "active" squalene also were obtained. This measurement of daily cholesterol synthesis by squalene kinetics minimizes patient inconvenience, is suitable for outpatient studies, and yields results in 4 weeks or less. Because of the rapidity of the rate of squalene synthesis, the results obtained reflect cholesterol synthesis over a period of less than 10 hr and are therefore uniquely applicable to unsteady state situations.
Analysis of the subtractive algorithm for greatest common divisors
Authors: Yao Andrew C. , Knuth Donald E.
Published: May 2006

The sum of all partial quotients in the regular continued fraction expansions of
m/n
, for 1 ≤
m
≤
n
, is shown to be 6π
-2
n
(ln
n
)
2
+
O
(
n
log
n
(log log
n
)
2
). This result is applied to the analysis of what is perhaps the oldest non-trivial algorithm for number-theoretic computations.
NH---S hydrogen bonds in Peptococcus aerogenes ferredoxin, Clostridium pasteurianum rubredoxin, and Chromatium high potential iron protein.
Authors: Adman E , Watenpaugh K D , Jensen L H
Published: May 2006

Results from refinement of the crystal structures of P. aerogenes ferredoxin and C. pasteurianum rubredoxin determined by x-ray diffraction show that there are 15-18 NH---S bonds in the former and six in the latter with lengths in the range 3.1-3.9 A. Earlier tritium exchange experiments are consistent with the presence of these hydrogen bonds in the ferredoxin structure and show that more peptide hydrogen atoms are available for exchange in apoferredoxin than in intact ferredoxin. Four types of NH---S bonds are observed and two of these are geometrically similar to the two types of 3(10) NH---O bonds. The existence of more NH---S bonds in ferredoxin than in high potential iron protein suggests why the -2 form of the Fe4S4 cluster is preferred in ferredoxin over the -1 form found in high potential iron protein. From comparison of Cys-X-Y-Cys sequences in rubredoxin, ferredoxin, and high potential iron protein we suggest that two Cys-X-Y-Cys-Z sequences, where Z may have conformation angles similar to glycine, are required to make a one-iron cluster, no more than one Cys-X-Y-Cys-Z-Gly sequence is required to form a Fe2S2 ferredoxin, and a Cys-X-Y-Cys-Gly sequence where Y has a conformation such that the cysteines bond to different iron atoms is necessary to form the tetrameric cluster.
Antibody against tuberlin: the specific visualization of cytoplasmic microtubules in tissue culture cells.
Authors: Weber K , Pollack R , Bibring T
Published: May 2006

Cytoplasmic microtubules in tissue culture cells can be directly visualized by immunofluorescence microscopy. Antibody against tubulin from the outer doublets of sea urchin sperm flagella decorates a network of fine cytoplasmic fibers in a variety of cell lines of human, monkey, rat, mouse, and chicken origin. These fibers are separate and of uniform thickness and are seen throughout the cytoplasm. The fibers disappear either in a medium containing colchicine or after subjection of the cells to low temperature. The same treatments do not destroy the microfilamentous structures that are visualized by means of antibody against actin. When tryspin-treated enucleated cells are replated and then stained with antibody against tubulin, the fibers can be seen to traverse the entire enucleated cytoplasm.
A very rapid effect of androgen on initiation of protein synthesis in prostate.
Authors: Liang T , Liao S
Published: May 2006

The initiation of protein synthesis by ribosomal particles of rat ventral prostate was studied by measuring ribosomal binding of an initiator (35-S)methionyl-tRNAf. The binding activity is dependent on ribosomes, GTP, and a prostate cytosol protein fraction. The 40S but not the 60S ribosomal subunit particles are active. The cytosol activity decreases rapidly within one hour after the rat is castrated. This loss is prevented by an intraperitoneal injection of 17beta-hydroxy-5-alpha-androstan-3-one (5-alpha-dihydrotestosterone). The cytosol activity can be stimulated almost immediately (within 10 min) after an intravenous injection of low dose (15 mug per rat) of 5-alpha-dihydrotestosterone into the castrated rat.
5'-Terminal m-7G(5')ppp(5')G-m-p in vivo: identification in reovirus genome RNA.
Authors: Furuichi Y , Muthukrishnan S , Shatkin A J
Published: May 2006

Methylated reovirus mRNA was synthesized in vitro in the presence of S-adenosyl-L-[methyl-3H]-methionine. Viral genome double-stranded RNA that was uniformly labeled with 32-P was isolated from purified virions. The RNAs were mixed and their 5'-terminal structures compared by electrophoretic and chromatographic analyses after enzymatic digestion. Both the mRNA and the corresponding strand in the genome RNA contain m-7G(5')ppp(5')G-m-pCp, indicating that infected cells synthesize viral RNA with blocked, methylated 5' termini.
A retarded rate of DNA chain growth in Bloom's syndrome.
Authors: Hand R , German J
Published: May 2006

The cytogenetic observation that homologous chromatid interchange occurs in Bloom's syndrome more often than normal prompted an investigation of DNA replication in that rare genetic disorder. Using DNA fiber autoradiography, an estimation was made of the rate of one component of ongoing DNA replication, DNA chain growth. The rate in Bloom's syndrome dermal fibroblasts in tissue culture was found to be significantly slower than that in normal control cells. (The rate was found to be normal in Fanconi's anemia cells.) The explanation for the retarded chain growth may be either that an enzyme concerned directly with semiconservative DNA replication is defective or that a defective enzyme not itself concerned directly with replication results in disturbed cellular metabolism which in turn affects replication.
Amino-acid sequence of parvalbumin from rabbit skeletal muscle.
Authors: Enfield D L , Ericsson L H , Blum H E , Fischer E H , Neurath H
Published: May 2006

Determination of the complete amino-acid sequence of rabbit skeletal muscle parvalbumin is described. The sequence of 86 of the 109 total residues was determined automatically by sequenator analyses of peptides obtained after cleavage with CNBr or with trypsin. The positions of the remaining 23 residues were determined by subtractive Edman degradation of tryptic and chymotryptic peptides. The protein has an acetylated amino terminus. Comparison of the rabbit parvalbumin with those from carp, hake, and pike and with the calcium binding subunit of rabbit muscle troponin indicates that these proteins are homologous. Among the parvalbumins a high degree of identity is observed, especially of residues involved in the binding of calcium or in the formation of the hydrophobic core.
Isolation of a low-molecular-weight serum component antigenically related to an amyloid fibril protein of unknown origin.
Authors: Linke R P , Sipe J D , Pollock P S , Ignaczak T F , Glenner G G
Published: May 2006

An amyloid fibril protein of unknown origin from a patient with systemic amyloidosis has been purified to homogeneous charge and size by gel filtration and two step isoelectric focusing. From crude antisera to the initial heterogeneous fibril protein, monospecific antibodies have been obtained by immunoabsorption with the immobilized purified amyloid protein. These antibodies have been used to identify an antigenically related serum component in whole sera of patients with and without amyloidosis. Chromatography on Sephadex G-200 in phosphate buffered saline of a patient's whole serum yields a component with an apparent molecular weight of approximately 200,000. Guanidine denaturation of this high-molecular-weight serum component followed by Sephadex G-100 column chromatography in 5 M guanidine affords an antigenically reactive protein with an apparent molecular weight of about 12,500. The antigenic similarity and molecular weight of the latter protein indicates that it could act as the smallest serum precursor of the tissue fibril protein in this group of cases of amyloidosis.
Sidechain torsional potentials and motion of amino acids in porteins: bovine pancreatic trypsin inhibitor.
Authors: Gelin B R , Karplus M
Published: May 2006

Conformational potentials of sidechains in the bovine pancreatic trypsin inhibitor have been studied with an empirical energy function. Calculated minimumenergy positions are in excellent agreement with the x-ray structure for sidechains in the core or at the surface of the protein; as expected, angles for sidechains that are directed out into the solvent do not agree with the calculated values. The contributions to the potentials are analyzed and compared with the potentials for the free amino acid. Although there is a large restriction in the available conformational space due to nonbonded interactions, the minimum energy positions in the protein are close to those of the free amino acid; the significance of this result is discussed. To estimate the effective barriers for rotation of the aromatic rings (tyrosine and phenylalanine), calculations are done in which the protein is permitted to relax as a function of the ring orientation. Thr resulting barriers, which are much lowere than the rigid rotation barriers, are used to evaluate the rotation rates; comparison is made with the available nuclear magnetic resonance data.
Methylated simian virus 40-specific RNA from nuclei and cytoplasm of infected BSC-1 cells.
Authors: Lavi S , Shatkin A J
Published: May 2006

Host cell and virus-specific poly(A)-containing RNAs isolated from nuclei and cytoplasm of monkey kidney cells infected with simian virus 40 contain different methylated nucleotides. In the cytoplasmic simian virus 40-specific RNA, about 75% of the radioactivity derived from (methyl-3-H)methionine was in N-6-methyladenosine (N-6mA) after digestion with Penicillium nuclease and bacterial alkaline phosphatase. The remainder was in a negatively charge component with properties of 5'-terminal structures, i.e., digestion with nucleotide pyrophosphatase and bacterial alkaline phosphatase released 2'-O-methyladenosine (A-m), 2'-O-methylguanosine (G-m), and 7-methylguanosine (m-7-G), consistent with a 5'-terminal structure of the type, m7-GpppNm. The nuclear virus-specific RNA contained N6mA, GM, 2'-O-methyluridine (U-m), and a smaller proportion (10%) of nuclease-, phosphatase-resistant presumptive 5' termini that also yielded A-m, G-m, and m7-G upon further hydrolysis. The infected cell nuclear and cytoplasmic RNAs that did not hybridize to DNA of simian virus 40 contained all four 2'-O-methylnucleosides. The possible role of methylation in the processing and translation of simian virus 40-specific mRNA is discussed.
Concerning Jahn-Teller Effects
Authors: Pearson Ralph G.
Published: May 2006

Jahn-Teller effects are grouped into two categories. The first arises from incomplete shells of degenerate orbitals. It includes the first-order Jahn-Teller effect, and the pseudo Jahn-Teller effect. The second arises from filled and empty molecular orbitals that are close in energy, and is the second-order Jahn-Teller effect. The two categories have quite different physical bases. As a result, geometric distortions produced by the first are quite small and normally lead to dynamic effects only. In favorable cases, the second-order Jahn-Teller effect produces very large distortions, including complete dissociation of a molecule. This can occur even when the relevant molecular orbitals are separated in energy by as much as 4 eV.
Species Richness of the Parasitic Fungi of British Trees
Authors: Strong Donald R. , Levin Donald A.
Published: May 2006

The species richness of fungi associated with British trees is described by a significant species/area curve (
r
= 0.53, 0.01 >
P
> 0.001). Introduced tree species cannot be shown to have fewer fungal species than natives, per unit distributional range about Britain. Also, among natives and among introductions, older host taxa do not have more fungal species than do younger ones. This indicates the species richness of fungi to rapidly reach the limit set by host range, within ecological time. The slope of the species/area relationship for fungi is one-fourth that for insects; we propose that this is due to the inherently greater dispersability of fungi. Finally, the species/area regression residuals for fungi are correlated with those for insects (
r
= 0.65, 0.001 >
P
), suggesting plant defense mechanisms may be generally effective to plant parasites, be they insects or fungi.
Two antigenically distinct species of human interferon.
Authors: Havell E A , Berman B , Ogburn C A , Berg K , Paucker K , Vilcek J
Published: May 2006

Rabbit antisera prepared against interferon produced in human fibroblast cell cultures stimulated with poly(1).poly(C) neutralized the activity of interferon preparations produced in various human fibroblast cultures timulated either with poly(1)poly)C) or with viruses. However, these antisera showed no detectable neutralizing activity against interferon produced in cultures of human leukocytes. On the other hand, most rabbit antisera against the human leukocyte interferon were active in neutralizing both homologous interferon and fibroblast interferons. A preparation of antiserum against leukocyte interferon, active against both leukocyte and fibroblast interferons, was shown by affinity chromatography to have two distinct antibody populations, one of which was specific for the fibroblast interferon. We conclude that the heterologous neutralizing activity of sera from rabbits immunized with leukocyte interferon is liekly to be due to the presence of two antigenic species of interferon. The major antigenic species of leukocyte interferon preparations (designated "Le") is distinct from huamn fibroblast interferon. The minor species of leukocyte interferon ("F") is either identical with, or closely related to, interferon produced in human fibroblast cultures.
Regulation of protein synthesis at the translational level in neuroblastoma cells.
Authors: Zucco F , Persico M , Felsani A , Metafora S , Augusti-Tocco G
Published: May 2006

Protein synthesis in reuroblastoma cells has been studied in a cell-free system. The activity of lysates from cells grown insuspension and monolayer has been compared. A higher level of activity has been found in monolayer cells. The activity of some components of the lysate that are involved in protein synthesis has been analyzed.The data suggest that the controlling step of protein synthesis in this system might be in the initiation process. The correlation between activation of protein synthesis and neurite outgrowth in monolayer cultures is discussed.
Ozone Model for Bonding of an O
2
to Heme in Oxyhemoglobin
Authors: Goddard William A. , Olafson Barry D.
Published: May 2006

Several rather different models of the Fe—O
2
bond in oxyhemoglobin have previously been proposed, none of which provide a satisfactory explanation of several properties. We propose a new model for the bonding of an O
2
to the Fe of myoglobin and hemoglobin and report
ab initio
generalized valence bond and configuration interaction calculations on FeO
2
that corroborate this model. Our model is based closely upon the bonding in ozone which recent theoretical studies have shown to be basically a biradical with a singlet state stabilized by a three-center four-electron pi bond. In this model, the facile formation and dissociation of the Fe—O
2
bond is easily rationalized since the O
2
always retains its triplet ground state character. The ozone model leads naturally to a large negative electric field gradient (in agreement with Mössbauer studies) and to
z
-polarized (perpendicular to the heme) charge transfer transitions. It also suggests that the 1.3 eV transition, present in HbO
2
and absent in HbCO, is due to a porphyrin-to-Fe transition, analogous to that of ferric hemoglobins (e.g., HbCN).
Solid tumor models for the assessment of different treatment modalities: I. Radiation-induced changes in growth rate characteristics of a solid tumor model.
Authors: Looney W B , Trefil J S , Schaffner J C , Kovacs C J , Hopkins H A
Published: May 2006

A computer program has been developed to quantitatively evaluate changes in tumor growth rates of a solid tumor model (hepatoma 3924A) after a series of radiation doses from 375 R to 3750 R. The computer-derived growth curves are simulated from the volumes of the individual tumors rather than from the mean tumor volume at any specific time point after treatment. The ability to generate data from a family of tumor growth curves permits a more precise evaluation of therapeutic effects on tumors than can be obtained with conventional methods. The quantitative determination of equivalent amounts of radiation needed to produce comparable 5-fluorouracil-induced changes in tumor growth rate has been made. The ability to determine quantitatively radiotherapeutic and chemotherapy equivalents on these solid tumor models has direct implications in regard to our effort to improve the treatment of cancer. At present no specific solid tumor or groups of solid tumors have provided all of the necessary information for clinical utilization in therapeutic scheduling of different forms of cancer treatment. Since solid tumors comprise the majority of human cancer, one of the primary objectives of these studies has been the establishment of a solid tumor model that could serve both as a system for devising improved therapeutic scheduling and for a better understanding of solid tumors.
Role of magnesium in Escherichia coli alkaline phosphatase.
Authors: Anderson R A , Bosron W F , Kennedy F S , Vallee B L
Published: May 2006

Alkaline phosphatase of E. coli, isolated by procedures which do not alter its intrinsic metal content, contains 1.3 +/- 0.3 g-atom of magnesium and 4.0 +/- 0.2 g-atom of zinc per molecule of molecular weight 89,000. Magnesium, the role of which has been unappreciated, significantly affects the function and structure of alkaline phosphatase containing either 2 or 4 g-atom of zinc per mole. Magnesium does not activate the apoenzyme but increases the activity of the enzyme containing 2 g-atom of zinc 4.4-fold and that of the enzyme containing 4 g-atom 1.2-fold. The results obtained with enzyme in which cobalt is substituted for zinc are analogous. Moreover, the absorption and electron paramagnetic resonance spectra of cobalt phosphatases reveal the effects of magnesium on cobalt coordination geometry. Addition of magnesium changes the spectral characteristics of the apoenzyme reconstituted with 2 g-atom of cobalt from predominantly octahedral to 4- or 5-coordinate geometry. These two classes of cobalt binding sites have been associated with catalysis and structure stabilization, respectively. Therefore, magnesium controls the occupancy of the catalytic and structural binding sites and modulates the resultant enzymatic activity. Hydrogen-tritium exchange was employed to determine the effects of magnesium on the conformational stability of phosphatase. Magnesium stabilizes the dynamic structural properties, both of apophosphatase and of enzyme containing 2 g-atom of zinc, which is further stabilized by 2 more zinc atoms. The role of magnesium and other metal ions in regulatory processes, only now beginning to be explored fully, will likely emerge as an important avenue for achievement of regulatory effects in metalloenzymes.
Thromboxanes: a new group of biologically active compounds derived from prostaglandin endoperoxides.
Authors: Hamberg M , Svensson J , Samuelsson B
Published: May 2006

An unstable [t1/2 at 37 degrees = 32 +/- 2 (SD) sec] intermediate, thromboxane A2, was detected in the conversion of prostaglandin G2 into 8-(1-hydroxy-3-oxopropyl)-9,12L-dihydroxy-5,10-heptadecadienoic acid (thromboxane B2) in platelets. The intermediate was trapped by addition of methanol, ethanol, or sodium azide to suspensions of washed human platelets incubated for 30 sec with arachidonic acid or prostaglandin G2. The structures of the resulting derivatives demonstrated that the intermediate possessed an oxane ring as in thromboxane B2 but lacked its hemiacetal hydroxyl group. Additional experiments using 18O2 or [2H8]arachidonic acid in the formation of thromboxane B2 and CH3O2H for the trapping of thromboxane A2, together with information on the t1/2 of the intermediate, indicated the presence of an oxetane structure in thromboxane A2. Incubation of arachidonic acid or prostaglandin G2 with washed platelets led to formation of an unstable factor that induced irreversible platelet aggregation and caused release of [14C]serotonin from platelets that had been incubated with [14C]serotonin. The properties and the mode of formation of this factor indicated that it was identical with thromboxane A2. Furthermore, evidence is presented that the more unstable and major component of rabbit aorta contracting substance (RCS) formed in platelets and guinea pig lung is also thromboxane A2.
Distinct penicillin binding proteins involved in the division, elongation, and shape of Escherichia coli K12.
Authors: Spratt B G
Published: May 2006

The varied effects of beta-lactam antibiotics on cell division, cell elongation, and cell shape in E. coli are shown to be due to the presence of three essential penicillin binding proteins with distinct roles in these three processes. (A) Cell shape: beta-Lactams that specifically result in the production of ovoid cells bind to penicillin binding protein 2 (molecular weight 66,000). A mutant has been isolated that fails to bind beta-lactams to protein 2, and that grows as round cells. (B) Cell division: beta-Lactams that specifically inhibit cell division bind preferentially to penicillin binding protein 3 (molecular weight 60,000). A temperature-sensitive cell division mutant has been shown to have a thermolabile protein 3. (C) Cell elongation: One beta-lactam that preferentially inhibits cell elongation and causes cell lysis binds preferentially to binding protein 1 (molecular weight 91,000). Evidence is presented that penicillin bulge formation is due to the inhibition of proteins 2 and 3 in the absence of inhibition of protein 1.
Substrate specificity of the cyclic AMP-dependent protein kinase.
Authors: Kemp B E , Bylund D B , Huang T S , Krebs E G
Published: May 2006

The protein substrate specificity of the catalytic subunit of rabbit skeletal muscle cyclic AMP-dependent protein kinase (EC 2.7.1.37; ATP:protein phosphotransferase) has been studied using genetic variants of beta casein. It was found that beta casein-B was phosphorylated at a much greater rate than beta caseins A1, A2, A3, or C. The enhanced phosphorylation of beta casein-B, as compared with the most common variant A2, was attributed to an arginine substitution for a serine at position 122, which caused a nearby residue, serine 124, to become a phosphorylation site for the protein kinase. These results further support the concept that the local primary structure is important in specificity and that arginine may be a specific determinant common to all the local phosphorylation site sequences recognized by the cyclic AMP-dependent protein kinase.
Metabolism of benzo[a]pyrene: conversion of (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene to highly mutagenic 7,8-diol-9,10-epoxides.
Authors: Thakker D R , Yagi H , Lu A Y , Levin W , Conney A H
Published: May 2006

Metabolites of (+/-)-trans 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene formed by a rat liver microsomes and by a highly purified monoxygenase system were analyzed by high-pressure liquid chromatography. Four stereoisomeric tetraols of 7,8,9,10-tetrahydrobenzo[a]pyrene, known solvolysis products of the two highly mutagenic stereoisomers of the 9,10-epoxide of the 7,8-dihydrodiol, were identified as products. The ratio of the two highly unstable diol epoxides formed (7 beta,8alpha-dihydroxy-9beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, diol epoxide 1; 7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, diol epoxide 2) ranged from about 1.7 to 0.4. The diol epoxides are sufficiently reactive to alkylate phosphate buffer (pH 7.4) at 37 degrees. Microsomes, particularly those from control animals, formed a substantial amount of an additional metabolite that appears to be phenolic. In analogy to benzo[a]pyrene, the metabolism of the 7,8-dihydrodiol shows similar induction after pretreatment of rats with phenobarbital or 3-methylcholanthrene. Neither diol epoxide appears to be a substrate for epoxide hydrase based on the ratis of tetraols formed in the presence or absence of epoxide hydrase. In view of the known carcinogenicity of benzo[a]pyrene 7,8-oxide and 7,8-dihydrodiol and of the marked mutagenicity of the stereoisomeric diol epoxides, both of these diol epoxides qualify for consideration as "ultimate carcinogen(s)" of benzo[a]pyrene.
Nitrofurans, a group of synthetic antibiotics, with a new mode of action: discrimination of specific messenger RNA classes.
Authors: Herrlich P , Schweiger M
Published: May 2006

Nitrofurans, a class of antibacterial drugs in extensive use, interferes with gene expression in a highly specific manner. While in the low dose range (0.5-25 mug/ml), 5-nitro-2-furfurylidene-1-aminohydantoin has no effect on transcription, it inhibits specifically the expression of one class of genes in translation. The specific inhibition concerns the inducible genes. The inhibition of messenger RNA expression occurs at the initiation step. The action of nitrofurans, thus, indicates heterogeneity in the population of mRNA molecules and in the translational machinery and suggests the possibility of selective translational control.
Differential synthesis of blocked and unblocked 5'-termini in reovirus mRNA: effect of pyrophosphate and pyrophosphatase.
Authors: Furuichi Y , Shatkin A J
Published: May 2006

Viral mRNA synthesized in vitro by reovirusassociated enzymes contained 5'-terminal ppG, GpppG, or m7GpppGm. Selective synthesis of one type of 5'-end was obtained by adjusting the composition of the transcription reaction mixture based on a series of reactions proposed for formation of blocked, methylated 5'-terminal sequences of mRNA (capformation). The presence of inorganic pyrophosphate increased the proportion of ppG 5'-ends, while addition of pyrophosphatase yielded mRNA with 5'-terminal GpppG, which in the presence of a methyl donor was converted to m7GpppGm.
A potassium ionophore (valinomycin) inhibits lymphocyte proliferation by its effects on the cell membrane.
Authors: Daniele R P , Holian S K
Published: May 2006

Valinomycin is a depsipeptide antibiotic which selectively translocates potassium across biologic membranes. This potassium ionophore was observed to inhibit phytohemagglutinin-stimulated blastogenesis and proliferation in human lymphocytes. The effect was not due to toxicity to the cells, nor appeared to be due to the effects of valinomycin as an uncoupler of oxidative phosphorylation. Furthermore, the inhibitory effect on phytohemagglutinin stimulated lymphocytes was prevented by increasing the potassium concentration of the external media. These results suggest that the interaction of mitogens with specific receptors at the cell membrane may involve mechanisms affecting cation fluxes and membrane potential. These ionic events may play a role in the transduction of membrane signals for lymphocyte stimulation.
Cells that express viral antigens but lack H-2 determinants are not lysed by immune thymus-derived lymphocytes but are lysed by other antiviral immune attack mechanisms.
Authors: Zinkernagel R M , Oldstone M B
Published: May 2006

Murine F9 teratoma cells do not express major transplantation antigens detectable by either serologic or alloreactive assays of thymus-dependent lymphocytes (T cells). Such cells can be infected with lymphocytic choriomeningitis virus or vaccinia virus, do express viral antigens on the cell surface, and can release infectious virus in amounts equivalent to those of other H-2 bearing murine cell lines. Immunologic injury of virus-infected F9 cells occurs after the addition of specific antiviral antibody and complement or of specific antiviral antibody and unsensitized lymphoid cells (antibody-mediated cell-dependent killing). In contrast, injury does not follow the addition of immune cytotoxic T cells. These results indicate that possession of H-2 antigens is not a requirement for a cell's infection by or production of virus. Further, expression of viral antigens on the cell's surface, although adequate for antibody-mediated immune injury, is by itself insufficient for direct T cell-mediated lysis. The major transplantation antigens thus probably represent the cell surface structures that are crucial for T-mediated cell wall damage that results in chromium release.
DNA gyrase: an enzyme that introduces superhelical turns into DNA.
Authors: Gellert M , Mizuuchi K , O'Dea M H , Nash H A
Published: May 2006

Relaxed closed-circular DNA is converted to negatively supercoiled DNA by DNA gyrase. This enzyme has been purified from Escherichia coli cells. The reaction requires ATP and Mg++ and is stimulated by spermidine. The enzyme acts equally well on relaxed closed-circular colicin E1, phage lambda, and simian virus 40 DNA. The final superhelix density of the DNA can be considerably greater than that found in intracellularly supercoiled DNA.
Activation of chromatin by acetylation of histone side chains.
Authors: Marushige K
Published: May 2006

The ability of calf thymus chromatin to support DNA-dependent RNA synthesis is markedly increased by modification of the histones with acetic anhydride. The extent of chemical acetylation of histones H2a, H2b, H3, and H4 required for the increase of template activity of the chromatin is within that which can be achieved enzymatically in the cell. The evidence suggests that the acetylation of histone side chains stimulates the rate of chain elongation during transcription of chromatin.
Courtship in Drosophila mosaics: sex-specific foci for sequential action patterns.
Authors: Hotta Y , Benzer S
Published: May 2006

Mosaic fate mapping is used to locate the foci determining sex-specific steps in the mating behavior of Drosophila. Male performance of following females and displaying wing vibration toward them requires that a focus inside the head be constituted of male tissue, regardless of the sex of the head sense organs, the legs, the wings, or the thoracic ganglion. For attempted copulation to occur, a second focus in the thoracic region must also be male. Courtship by males is induced by a posteriorly located focus in the female, but an anterior female focus determines receptivity to attempted copulation. The interplay of male and female foci in the complex behavioral sequence is delineated.
Localization of gene functions in polyoma virus DNA.
Authors: Feunteun J , Sompayrac L , Fluck M , Benjamin T
Published: May 2006

Polyoma virus mutants of four functionally distinct groups have been mapped by the marker rescue technique using restriction enzyme fragments of wild-type viral DNA. Nontransforming host-range mutants map in the proximal part of the early region of the viral genome. The same DNA fragment that restores a normal host range also restores normal transforming ability to these mutants. ts-25D, a temperature-sensitive (ts)-a class mutant, maps in the distal part of the early region. ts-3 and ts-1260 map in the proximal and distal parts of the late region, respectively.
Metal-metal bond lengths in complexes of transition metals
Authors: Pauling Linus
Published: May 2006

In complexes of the transition metals containing clusters of metal atoms the cobalt-cobalt bond lengths are almost always within 1 pm of the single-bond value 246 pm given by the enneacovalent radius of cobalt, whereas most of the observed iron-iron bond lengths are significantly larger than the single-bond value 248 pm, the mean being 264 pm, which corresponds to a half-bond. A simple discussion of the structures of these complexes based on
spd
hybrid orbitals, the electroneutrality principle, and the partial ionic character of bonds between unlike atoms leads to the conclusion that resonance between single bonds and no-bonds would occur for iron and its congeners but not for cobalt and its congeners, explaining the difference in the bond lengths.
A moment equation description of magnetic reversals in the earth
Authors: Robbins K. A.
Published: May 2006

Low order moments of the alpha dynamo equations in a geophysical regime are related to the dependent variables in a reversing disk dynamo. The link suggests that nonperiodic reversal is an intrinsic feature of the alpha dynamo equations provided the forcing is vigorous and the toroidal and poloidal magnetic fields are sufficiently out of phase. The nonuniformities in reversal frequency are then attributable to subcritical instability.
Vertical displacement of membrane proteins mediated by changes in microviscosity.
Authors: Borochov H , Shinitzky M
Published: May 2006

Membrane proteins of intact human erythrocytes were labeled with two fluorescent sulfhydryl reagents. The tagged cells were then subjected to simultaneous liposome treatments for either depletion or enrichment of membrane cholesterol content. Cholesterol depletion, which reduces membrane microviscosity, was followed by a series of fluorescence changes all indicating masking of the membrane proteins. Conversely increasing the membrane microviscosity by cholesterol enrichment resulted in an appreciable increase of the protein exposure to the aqueous surrounding. These findings strongly suggest that membrane proteins may be vertically displaced upon changes in lipid fluidity, a mechanism that may play a significant role in modulation of antigens and receptors in vivo.
Order of transcription of genes of vesicular stomatitis virus.
Authors: Ball L A , White C N
Published: May 2006

The effect of ultraviolet radiation on the expression of the genes of vesicular stomatitis virus (VSV) was studied in a cell-free system which executed coupled transcription and translation of the viral genes. In this system, which contained detergent-activated virus and a cytoplasmic extract of mouse L-cells, three of the five viral proteins (N, NS, and M) were synthesized accurately and efficiently; a putative precursor to the viral glycoprotein (G) was also made, but synthesis of the L protein was not detected. In response to irradiation of VSV, the synthesis of each protein in the coupled system displayed a characteristic single-hit inhibition. This permitted calculation of the apparent target-sizes for expression of the different viral genes relative to the entire genome (3.6 to 4.0 X 10(6) daltons) as measured by loss of infectivity. These are: N, 0.55 X 10(6); NS, 0.83 X 10(6); M, 1.12 X 10(6); G, 1.76 X 10(6) daltons of RNA. Only the N protein gene has a target-size which corresponds to that predicted from the molecular weight of its messenger RNA (molecular weight: 0.55 X 10(6)). The target-sizes for the other three genes are two to four times larger than expected, and are not proportional to the molecular weights of their corresponding messenger RNAs (molecular weights: NS, 0.28 X 10(6); M, 0.28 X 10(6); G, 0.7 X 10(6)). The polar effect of UV irradiation is inconsistent with independent transcription of each of the genes of VSV. Rather, the target-sizes appear to be cumulative, suggesting that trnascription initiates at a single point on VSV RNA and proceeds in the order 3'-N-NS-M-G-(L)-5'.
House monotone apportionment schemes
Authors: Birkhoff Garrett
Published: May 2006

An empirical comparison is given of two schemes of Congressional apportionment: Huntington's generally accepted Equal Proportion scheme, and a new “house-monotone” Quota scheme. Evidence is given to show that Quota tends to underrepresent small states.
Novel mechanism for translational control in regulation of ferritin synthesis by iron.
Authors: Zähringer J , Baliga B S , Munro H N
Published: May 2006

Poly(A)-containing RNA was isolated from the polyribosomal and post-ribosomal fractions of the livers of normal and iron-treated rats. These RNA fractions were then translated in a wheat germ system to provide a measure of the amount of ferritin mRNA present in each fraction. Following iron administration, there was a 2-fold increase in the amount of ferritin mRNA in the polyribosomal fraction. This increase was not inhibited by prior treatment of the rats with actinomycin D or cordycepin, suggesting a cytoplasmic control mechanism. In normal rats, the post-ribosomal fraction contained an amount of ferritin mRNA equal to that in the polyribosomes. When iron was administered, this untranslated ferritin mRNA became reduced to negligible quantities, thus accounting for the doubling of the ferritin mRNA content of the polyribosomal fraction. A scheme is proposed in which translation of the ferritin mRNA in the post-ribosomal fraction is prevented by adhering ferritin subunits. Iron administration removes this inhibition of the translation of ferritin mRNA by promoting aggregation of these subunits into ferritin.
Bedload measurements, East Fork River, Wyoming
Authors: Leopold Luna B. , Emmett William W.
Published: May 2006

A bedload trap in the riverbed provided direct quantitative measurement of debris-transport rate in the East Fork River, Wyoming, a basin of 466 km
2
drainage area. Traction load moves only during the spring snow melt season. Data collected in three spring runoff seasons during which a peak flow of 45 m
3
/s occurred showed that transport rate is correlated with power expenditure of the flowing water and at high flows becomes directly proportional to power as suggested by Bagnold.
Synthesis of murine leukemia virus proteins associated with virions assembled in actinomycin D-treated cells: evidence for persistence of viral messenger RNA.
Authors: Levin J G , Rosenak M J
Published: May 2006

Murine leukemia virus particles assembled in actinomycin D-treated cells were detected by determination of reverse transcriptase [RNA-dependent DNA polymerase (nucleotidyltransferase)] activity and by radioimmunoassay of the major virion protein, p30. The levels of enzyme activity and p30 protein were both 30-40% relative to the control over an 8 hr period, whereas after 3 or 4 hr infectivity was reduced by 95%. Thus, virions produced in the absence of RNA synthesis represent a fairly homogeneous population of defective particles. Although RNA synthesis is not necessary for virus assembly, protein synthesis is required. Treatment of cells with 10 mug/ml of cycloheximide reduced virus production by 80-85% within 2 hr, and by greater than 95% at later times. As might be expected from this finding, viral protein synthesis accompanies virus assembly in actinomycin D-treated cells. Newly synthesized proteins associated with the defective particles were identical with those found in standard virions and were present in the correct proportions. The results demonstrate that viral mRNA persists in cells in which RNA synthesis is blocked and continues to direct viral protein synthesis with a functional half-life of approximately 6-8 hr. Since viral mRNA is not packaged in virions even when viral RNA synthesis is shut off [Levin et al. (1974) J. Virol. 14, 152-161], we propose that murine leukemia virus-infected cells contain two nonequilibrating pools of intracellular viral RNA molecules, one associated with polyribosomes and one which is encapsidated into extracellular particles.
Birds on islands in the sky: Origin of the montane avifauna of Northern Melanesia
Authors: Mayr Ernst , Diamond Jared M.
Published: May 2006

Biogeographers have long been fascinated by the disjunct distributions of species stranded on mountaintops. This paper analyzes, for the montane bird populations of Northern Melanesian islands, how many such populations there are, why they are restricted to mountains, and how they dispersed to mountains. The number of populations increases with island elevation and with montane area, and decreases with lowland area, exemplifying the problem of continental species diversity. Most species with montane populations on some island(s) have sea-level populations on some other island(s). These altitudinal niche shifts can be variously related to interisland differences either in altitudinal distribution of area or else in competitive pressure in the lowlands or mountains. Restriction of Northern Melanesian bird populations to mountains is more often due to lowland competitors than to inability to survive under the physical conditions of the lowlands. Of four possible mechanisms for the origin of a montane population (referred to as jumping, land-bridge crossing, trickling, and push-pull shifts), only the first and last have been significant for Northern Melanesian birds.
Morphogenesis of the bacterial division septum: a new class of septation-defective mutants.
Authors: Weigand R A , Vinci K D , Rothfield L I
Published: May 2006

A new class of mutants of Salmonella typhimurium (lkyD mutants) are described. The mutants are defective in morphogenesis of the division septum, and are characterized by a failure of the outer membrane to invaginate despite normal ingrowth of the cytoplasmic membrane and murein layers of the growing septum. The cell envelopes of the mutants show a significant decrease in the bound form of murein-lipoprotein and a corresponding increase in the free form of the lipoprotein. This suggests that the morphogenic defect may result from a defect in formation of covalent bonds between the free lipoprotein of the outer membrane and the murein of the nascent septum.
Induction if immunological tolerance to the major antigenic determinant of penicillin: a therapeutic approach to penicillin allergy.
Authors: Chiorazzi N , Eshhar Z , Katz D H
Published: May 2006

High titered IgE, IgG, and IgM antibody responses to the major antigenic determinant of penicillin, the benzylpenicilloyl hapten, were elicited by the intraperitoneal injection of the hapten coupled to keyhole limpet hemocyanin mixed with the appropriate adjuvant. However, treatment of such mice with the benzylpenicilloyl derivatized synthetic copolymer of D-glutamic acid and D-lysine, either before or after primary immunization, resulted in significant suppression of the subsequent anti-benzylpenicilloyl antibody responses of the IgE and IgG classes, as measured at the humoral and cellular levels. The state of tolerance induced by benzylpenicili-poly(DGlu, Lys) was highly specific, of long duration, and could be induced in a manner that would be appropriate for clinical use. These results provide a direct demonstration of the potential application of the poly(DGlu, Lys) immunotherapeutic approach to penicillin allergy in humans.
Species-distance relation for birds of the Solomon Archipelago, and the paradox of the great speciators
Authors: Diamond Jared M. , Gilpin Michael E. , Mayr Ernst
Published: May 2006

For scattered remote islands and for likely forms of immigration and extinction curves, the equilibrium theory of island biogeography leads to the prediction [unk]
2
log
S/[unk]A[unk]D
> 0, where
S
is the number of species on an island,
A
island area, and
D
island distance from the colonization source. This prediction is confirmed for birds of the Solomon Archipelago. Bird species can be classified into three types according to how distance affects their distributions: non-water-crossers, which are stopped completely (usually for psychological reasons) by water gaps of even 1 mile; short-distance colonists, successful at colonizing close but not remote islands; and long-distance colonists, successful at colonizing remote as well as close islands. Almost all of the “great speciators”, the species for whose inter-island geographic variation the Solomons are famous, prove to be short-distance colonists. Lack's interpretation of the decrease in
S
with
D
is shown to rest on incorrect assumptions.
Antibody evidence for different conformational states of ADP, ATP translocator protein isolated from mitochondria.
Authors: Buchanan B B , Eiermann W , Riccio P , Aquila H , Klingenberg M
Published: May 2006

Consistent with the previously proposed reorientation mechanism for the ADP,ATP translocator protein of mitochondria, evidence has now been obtained for the existence of two distinct conformational states of the isolated translocator protein. Previous studies indicated that when the mitochondrial translocator protein is in the c-state(i.e., when its binding site faces the cytosol side) the protein binds primarily the ligand carboxyatractylate (CAT), and when the translocator protein is in the m-state(i.e., when its binding site faces the mitochondrial matrix) the translocator protein binds primarily bongkrekate. Direct evidence for this formulation has now come from the application of antibodies to the isolated translocator protein-ligand complex. Two antibodies were produced against the ADP,ATP translocator protein isolated from beef heart mitochondria. One antibody, which was produced against the protein isolated as the CAT-binding protein complex, was found to be highly specific for that complex and did not react with the protein in the conformation state conferred by the bongkrekate ligand. This antibody did not cover the CAT-binding site, as evidenced by the exchange of unlabeled CAT with [35S]CAT bound to the translocator protein. However, the same antibody inhibited a transition of the protein from the c-state to the m-state, as evidenced by an inhibition of the displacement of[35S]CAT by bongkrekate (added jointly with ADP). It appears, therefore, that the antibody immobilized the translocator protein in the c-state. The second antibody produced against the (somewhat less pure) ADP,ATP translocator protein, isolated as the bongkrekate-binding protein complex, did not react with the CAT-binding protein. Thus, the second antibody appeared to be specific for the translocator protein in the m-state. Neither antibody inhibited mitochondrial ADP,ATP transport.