bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular mechanism of inhibition of firefly luminescence by local anesthetics.
Authors: Ueda I , Kamaya H , Eyring H
Published: May 2006

The kinetics of the action of local anesthetics upon firefly luciferin and luciferase systems is presented. Clinical concentrations of local anesthetics inhibited this ATP-induced luminescence in a dose-dependent manner. From the effects of temperature and pH upon the inhibitory action of the local anesthetics, it is concluded that hydrophobic ligand-enzyme interaction is the predominant cause of the inhibition, but hydrophilic interaction also contributes to the inhibition to a lesser degree. A molecular theory of anesthesia is outlined which postulates that release of electrostricted water molecules from the hydrophilic parts of the enzyme due to the protein conformational changes induced by anesthetics is the cause of the decreased luminescence. A similar mechanism is expected to occur at the cell membrane, which probably dehydrates the sodium channel and suppresses the conductance of this ion across the membrane. These events lead to a volume expansion of the total system, and the system becomes reactive to a pressure which reverses the anesthesia by shifting the equilibrium to the nonanesthetized original volume. The pressure antagonism of anesthesia can be explained by this overall volume expansion and not by a mere swelling of the cell membrane.
Mutants of Balb/c 3T3 fibroblasts defective in adhesiveness to substratum: evidence for alteration in cell surface proteins.
Authors: Pouysségur J M , Pastan I
Published: May 2006

Two mutants of Balb/c 3T3 cells defective in adhesiveness to substratum have been isolated. After exposure to a mutagen a cell population was treated with prostaglandin E1 and methylisobutylxanthine to elevate the cells 3':5'-cyclic AMP levels and adhesion to the substratum; then, loosley adherent cells were harvested by gentle detachment. After four cycles of selection two clones were isolated. Both are characterized by a round morphology and a decreased adhesion to substratum. The defect in adhesion appears to be responsible for the change in cell shape, since the mutant cells become flattened and look similar to wild-type cells when treated with dibutyryl cyclic AMP even though their adhesiveness remains decreased. Further, the surface of both mutants is chemically altered. Lactoperoxidase-catalyzed iodination of the cell surface shows that two iodinated polypeptides (molecular weight, Mr, 90,000 and 135-140,000) present in wild-type cells are not detected on the surface of the mutants, and another iodinated band (110-120,000 Mr) is markedly decreased. In addition, one mutant is also missing the high-molecular-weight (230,000) cell surface protein that is sensitive to transformation. No changes have been found in the content of cyclic AMP or free or polymerized tubulin. The exponential growth rate and saturation density are not altered in these adhesion--eficient cells. This last result suggests that modulation of adhesion to substratum per se does not play an important role in the growth control of Balb/c 3T3 cells in vitro.
Inheritance of killer phenotypes and double-stranded RNA in Ustilago maydis.
Authors: Koltin Y , Day P R
Published: May 2006

Three different killer specificities in U. maydis are inherited cytoplasmically and transmitted by cell fusion. Each killer generates low frequencies of specifically immune forms in crosses with sensitive strains. The properties of immunity to each killer are also inherited cytoplasmically and transmitted by cell fusion. Killer strains carry virus-like particles about 41 nm in diameter. Each killer possesses distinct double-stranded RNA components that range in molecular weight from 0.46 X 10(6) to 2.9 X 10(6). Two components are shared by all three killers. Immune strains possess new forms. Crosses and heterokaryons between different killers revealed unilateral or mutual restrictions that prevent inclusion of two killer specificities in the same cell.
Evolution, population dynamics, and stability
Authors: Allen P. M.
Published: May 2006

By treating mutant populations as fluctuations relating to the structural stability of the equations of population dynamics, a criterion is developed permitting the prediction of long-term population trends in an evolving eco-system. As an illustration it is shown that the ratio of predator to prey biomass increases under the effects of their combined evolution.
Escherichia coli thioredoxin: a subunit of bacteriophage T7 DNA polymerase.
Authors: Mark D F , Richardson C C
Published: May 2006

T7 DNA polymerase (DNA nucleotidyltransferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7) is composed of an 84,000 dalton protein specified by the gene 5 of the phage and a 12,000 dalton protein (TsnC protein) specified by the tsnC gene of E. coli [Modrich, P. & Richardson, C. C. (1975) J. Biol. Chem. 250 5515-5522]. Both proteins are necessary for T7 DNA polymerase activity and for the replication of T7 DNA. The TsnC protein is identical to thioredoxin of E. coli by the following criteria: (1) Homogeneous preparations of both proteins have TsnC and thioredoxin activity. (2) Both proteins show similar stability to heat. (3) They have identical mobilities, corresponding to a molecular weight of 12,000, on polyacrylamide gels containing sodium dodecyl sulfate. (4) Their amino-acid compositions are indistinguishabe. (5) Antibody prepared against thioredoxin inhibits TsnC activity. (6) TsnC protein isolated from purified T7 DNA polymerase has thioredoxin activity. In addition, preparations of T7 DNA polymerase itself exhibit thioredoxin activity and are partially inhibited by antibody to thioredoxin.
Surface membrane carbohydrate alterations of a flagellated protozoan mediated by bacterial endosymbiotes.
Authors: Dwyer D M , Chang K P
Published: May 2006

Crithidia oncopelti, a parasitic trypanosomatid protozoan of insects, normally contains intracellular symbiotic bacteria. As shown earlier, the protozoa can be rid of their endosymbiotes by chloramphenicol, producing a symbiote-free cell line. Here surface-membrane carbohydrate ligands of the symbiote-containing and symbiote-free strains were compared by lectin-mediated agglutination, lectin-ultrastructure localization. [3H] lectin-binding, and fluorescent lectin staining. Symbiote-free organisms consistently had 3-fold higher agglutination titers than symbiote-containing cells with concanavalin A. Conversely, symbiote-containing flagellates had 2- to 3-fold greater agglutination titers with a fucose-binding lectin than symbiote-free organisms. Ultrastructure results showed that more of concanavalin A-horseradish peroxidase-diaminobenzidine reaction product was present at the surface of symbiote-free than on symbiote-containing cells. Treatment with [3H]concanavalin A revealed that surface membrane sites available per cell for [3H]lectin-binding ranged from 6.2 to 7.4 x 10(4) and from 24 to 27 x 10(4) for symbiote-containing and symbiote-free organisms, respectively, i.e., the mean binding level of the latter for the lectin was 3.5 times greater than that of the former. Moreover, symbiote-free cells fluoresced more than symbiote-containing organisms after staining with fluorescein-labeled concanavalin A. Apparently, the prokaryotic endosymbiotes somehow alter the quantity of saccharide ligands in the C. oncopelti surface membrane.
Influence of polyunsaturated fatty acids on survival of skin allografts and tumor incidence in mice.
Authors: Mertin J , Hunt R
Published: May 2006

Subcutaneous or oral administration of the polyunsaturated fatty acid linoleic acid prolongs survival of skin allografts in mice. Mice fed on a diet deficient in polyunsaturated fatty acids show a relative immunopotentiation, as indicated by accelerated skin allograft rejection and decreased incidence and rate of development of methylcholanthrene-induced tumors. These observations support the hypothesis that polyunsaturated fatty acids take part in immunoregulatory mechanisms.
Transcription in yeast: alpha-amanitin sensitivity and other properties which distinguish between RNA polymerases I and III.
Authors: Schultz L D , Hall B D
Published: May 2006

Three peaks of DNA-dependent RNA polymerase (RNA nucleotidyltransferase) activity are resolved by chromatography of a sonicated yeast cell extract on DEAE-Sephadex. The enzymes, which are named RNA polymerases I, II, and III in order of elution, show similar catalytic properties to the vertebrate class I, class II, and class III RNA polymerases, respectively. Yeast RNA polymerase III is readily distinguished from yeast polymerase I by its biphasic amnonium sulfate activation profile with native DNA templates, greater enzymatic activity with poly[d(I-C)] than with native salmon sperm DNA, and distinctive chromatographic elution positions from DEAE-cellulose (0.12 M ammonium sulfate) compared with DEAE-Sephadex (0.32 M ammonium sulfate). The three yeast RNA polymerases also show significant differences in alpha-amanitin inhibition. RNA polymerase II is the most sensitive (50% inhibition at 1.0 mug of alpha-amanitin per ml). Contrary to the results for vertebrate systems, yeast polymerase I can be completely inhibited by alpha-amanitin at high concentrations (50% inhibition at 600 mug/ml) while yeast RNA polymerase II BEGINS TO SHOW SIGNIFICANT INHIBITION ONLY AT CONCENTRATIONS EXCEEDING 1 MG/ML. Therefore, yeast RNA polymerases I and III show a pattern of alpha-amanitin sensitivity that is the reverse of that seen for the analogous vertebrate RNA polymerases.
Activation and nuclear translocation of protein kinase during transsynaptic induction of tyrosine 3-monooxygenase.
Authors: Costa E , Kurosawa A , Guidotti A
Published: May 2006

The tyrosine-3-monooxygenase activity [L-tyrosine, tetrahydropteridine: oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2] of rat adrenal medulla is induced 20-24 hr after the injection of reserpine (16 mumol/kg intraperitoneally). This and other inducing stimuli increase the 3': 5'-cyclic AMP (cAMP) content in the medulla for longer than 60 min and activate the cAMP-dependent protein kinase (ATP: protein phosphotransferase; EC 2.7.1.37) for several hours. Corticotropin (ACTH), dopamine, and propranolol do not induce the monooxygenase, but elicit an increase in the cAMP content of the medulla which fails to activate protein kinase and lasts less than 1 hr. A high- and low-molecular-weight protein kinase are separated by gel filtration from the 20,000 X g pellet extract of adrenal medulla homogenate. The activity of the low-molecular-weight enzyme is expressed as its ability to phosphorylate histone. The protein kinase activity of the pellet is increased between 3 and 17 hr after reserpine injection. Our evidence indicates that this increase is due to a translocation from cytosol to subcellular structures of a kinase that utilizes lysine-rich histone as phosphate acceptor. The protein kinase activity that is extracted from a purified nuclear fraction prepared from the adrenal medulla of rats injected 7 hr previously with reserpine is greater than that extracted from medulla of saline-treated rats.
Dephosphorylation of nonhistone proteins specifically alters the pattern of gene transcription in reconstituted chromatin.
Authors: Kleinsmith L J , Stein J , Stein G
Published: May 2006

A nonhistone phosphatase devoid of detectable protease activity has been purified from nuclear sap by chromatography on DEAE-Sephadex. After linkage to an insoluble agarose matrix, this enzyme was used to dephosphorylate nonhistone proteins obtained from S-phase HeLa cells. Chromatin reconstituted with these dephosphorylated proteins exhibited roughly a 50% reduction in the overall number of initiation sites available for transcription when compared to controls. Specific measurements of transcription of histone genes with use of a complementary DNA probe showed that genes coding for histones are preferentially inhibited after nonhistone dephosphorylation. These results provide the first direct support for the theory that phosphorylation of nonhistone proteins is involved in regulating the availability of individual genes for transcription.
Hydrogen evolution: A major factor affecting the efficiency of nitrogen fixation in nodulated symbionts
Authors: Schubert Karel R. , Evans Harold J.
Published: May 2006

Nitrogenase-dependent hydrogen evolution from detached legume nodules and from reaction mixtures containing cell-free nitrogenase has been well established, but the overall effect of hydrogen evolution on the efficiency of nitrogen fixation
in vivo
has not been critically assessed. This paper describes a survey which revealed that hydrogen evolution is a general phenomenon associated with nitrogen fixation by many nodulated nitrogen-fixing symbionts. An evaluation of the magnitude of energy loss in terms of the efficiency of electron transfer to nitrogen, via nitrogenase, in excised nodules suggested that hydrogen production may severely reduce nitrogen fixation in many legumes where photosynthate supply is a factor limiting fixation. With most symbionts, including soybeans, only 40-60% of the electron flow to nitrogenase was transferred to nitrogen. The remainder was lost through hydrogen evolution.
In situ
measurements of hydrogen evolution and acetylene reduction by nodulated soybeans confirmed the results obtained with excised nodules. In an atmosphere of air, a major portion of the total electron flux available for the reduction of atmospheric nitrogen by either excised nodules or intact nodulated plants was utilized in the production of hydrogen gas. Some non-leguminous symbionts, such as
Alnus rubra
, and a few legumes (i.e.,
Vigna sinensis
) apparently have evolved mechanisms of minimizing net hydrogen production, thus increasing their efficiency of electron transfer to nitrogen. Our results indicate that the extent of hydrogen evolution during nitrogen reduction is a major factor affecting the efficiency of nitrogen fixation by many agronomically important legumes.
Heat mutagenesis in bacteriophage T4: the transition pathway.
Authors: Baltz R H , Bingham P M , Drake J W
Published: May 2006

G-C leads to A-T transitions are induced by heat, and arise from the deamination of cytosine (5-hydroxymethylcytosine in the case of bacteriophage T4) generating uracil. The reaction is proton-catalyzed, and is also characteristic of acid mutagenesis. Mutation rates and activation energies of mutation are site-specific, and are presumably influenced by neighboring bases. Rates of heat-induced mutation in bacteriophage T4 under conditions of temperature, pH, and ionic strength similar to those prevailing in higher eukaryotic cells suggest that heat mutagenesis may present a serious challenge to organisms with large genomes, and may comprise an important determinant of the rates of spontaneous mutation.
Cotransfer of two linked human genes into cultured mouse cells.
Authors: Willecke K , Lange R , Krüger A , Reber T
Published: May 2006

Two linked human genes which code for the expression of cytosol thymidine kinase (ATP:thymidine 5'-phosphotransferase, EC 2.7.1.75) and galactokinase (ATP:D-galactose 1-phosphotransferase, EC 2.7.1.6) have been cotransferred via purified metaphase chromosomes from the human lymphoblastoid cell line WI-L2a, into mouse L-cells [B82 and LM(TK-)]. Both genes have previously been shown to be closely linked on the human chromosome E17, band q21-22. Coexpression of both human enzyme markers was detected in two out of eight gene transfer clones, whilst the remaining six clones contained only human cytosol thymidine kinase, as shown by electrophoretic techniques. A further 23 human enzyme markers corresponding to 15 different human chromosomes were found to be absent in these gene transfer clones. No human chromosome or chromosomal fragment could be detected by karyotype analyses. Some of the gene transfer clones rapidly lost the transferred donor material when grown in nonselective medium, whereas others expressed a stable phenotype under these conditions. Prolonged maintenance in selective medium favors the survival of gene transfer cells expressing a stable phenotype. Possibly these cells harbor the donor genes integrated into a recipient chromosome.
Immunoglobulin allotypes of rabbit kappa chains: polymorphism of a control mechanism regulating closely linked duplicated genes?
Authors: Farnsworth V , Goodfliesh R , Rodkey S , Hood L
Published: May 2006

The amino acid sequence of the constant (CK) region from the kappa immunoglobulin chains of a b9 rabbit is compared with the CK sequences, taken from the literature, of a b4 rabbit. These CK regions differ by 33% of their amino acid sequences and by three sequence insertions or deletions (sequence gaps). These extensive differences together with other published observations suggest that the b9 and b4 CK genes may not be simple alleles, but rather they may be encoded by closely linked CK genes present in every rabbit whose expression is regulated by a polymorphic control mechanism.
Human papilloma virus DNA: physical mapping and genetic heterogeneity.
Authors: Gissmann L , Hausen H Z
Published: May 2006

The molecular weight of three preparations of human papilloma virus DNA derived from different plantar warts was determined by agarose gel electrophoresis or electron microscopic contour length measurement. It was found to amount to approximately 4.9 X 10(6). Analysis of this DNA after sequential digestion by four different restriction endonucleases (EcoRI, Bam, Hind II, and Hind III) permitted physical mapping of the cleavage sites. Two of the three DNA preparations revealed an identical cleavage pattern, whereas the third one contained two additional cleavage sites.
Porphyria variegata and porphyria cutanea tarda in siblings: chemical and genetic aspects (addendum).
Authors: Watson C J , Cardinal R A , Bossenmaier I , Petryka Z J
Published: May 2006

A porphyria kindred in which the index case has porphyria variegata had also been shown to include a case of porphyria cutanea tarda, typical both from chemical and clinical features. The possibility that this was purely acquired rather than genetic seemed unlikely, but could not be wholly excluded. Recently, a niece of both of these cases, although asymptomatic, has been found to conform chemically with porphyria cutanea tarda, including the excretion of the isocoproporphyrin series, and thus represents the second case of this form of porphyria in this family. This strengthens the concept of genetic heterogeneity in this kindred and supports the suggestion of a double heterozygosity, as proposed in the primary paper [Watson, C.J. et al. (1975) Proc. Nat. Acad. Sci. USA 72, 5126-5129].
Simple synthesis of a 4a-hydroperoxy adduct of a 1,5-dihydroflavine: preliminary studies of a model for bacterial luciferase.
Authors: Kemal C , Bruice T C
Published: May 2006

The solution chemistry of N(5)-alkyl flavinium cations and radical species formed by their le- reduction are discussed. Previously unknown, the 4a-flavine hydroperoxides are established to be formed on reaction of N(5)-alkyl flavinium cations with H2O2 or on reaction of N(5)-alkyl-1, 5-dihydroflavines with 3O2. The stability of the 4a-flavine hydroperoxide species is exemplified in the isolation and characterization of 4a-hydroperoxy-N(5)-ethyl-3-methyl-lumiflavine. 4a-Flavine hydroperoxide compounds are shown to be stronger oxidants than H2O2, and to undergo a chemiluminescent reaction in the presence of an aldehyde. Preliminary observations on the chemiluminescent reaction of 4a-flavine hydroperoxides + RCHO are provided, and these are compared to those in the literature dealing with the bioluminescence of bacterial luciferase in the presence of 3O2 and RCHO.
Unstable spiral modes in disk-shaped galaxies
Authors: Lau Y. Y. , Lin C. C. , Mark James W.-K.
Published: May 2006

The mechanisms for the maintenance and the excitation of trailing spiral modes of density waves in diskshaped galaxies, as proposed by Lin in 1969 and by Mark recently, are substantiated by an analysis of the gas-dynamical model of the galaxy. The self-excitation of the unstable mode in caused by waves propagating outwards from the corotation circle, which carry away angular momentum of a sign opposite to that contained in the wave system inside that circle. Specifically, a simple dispersion relationship is given as a definite integral, which allows the immediate determination of the pattern frequency and the amplification rate, once the basic galactic model is known.
Comparative study of alkaline phosphatase activity in lymphocytes, mitogen-induced blasts, lymphoblastoid cell lines, acute myeloid leukemia, and chronic lymphatic leukemia cells.
Authors: Neumann H , Klein E , Hauck-Granoth R , Yachnin S , Ben-Bassat H
Published: May 2006

Alkaline phosphatase [orthophosphoricmonoester phosphohydrolase (alkaline pH optimum), EC 3.1.3.1] purified from a Burkitt lymphoma cell line (Daudi) and Moloney-virus-induced murine leukemia (YAC) showed unique catalytic properties in substrate specificity and inhibition by cysteamine-S-phosphate. It migrated on polyacrylamide gel electrophoresis in a single activity band. Alkaline phosphatase with similar properties was found in several human lymphoblastoid cell lines, in chronic lymphatic leukemic cells, in organs of leukemic mice, and in sera of patients with certain lymphoproliferative disorders.
Elucidation of hydrocarbon structure in an enzyme-catalyzed benzo[a]pyrene-poly (G) covalent complex.
Authors: Meehan T , Straub K , Calvin M
Published: May 2006

The carcinogen, benzo[a]pyrene, was covalently attached to poly (G) by liver microsomes from rats pretreated with 3-methylcholanthrene. The complex was hydrolyzed with enzymes or base and products were isolated by Sephadex chromatography. Absorbance and fluorescence spectra of the products fit that of red-shifted pyrene aromatic system and suggest that metabolism has occurred at the 7-, 8-, 9-, and 10-positions of the hydrocarbon. Benzanthracene or chrysene fluorescence were not observed in these preparations. Benzo[a]pyrene derivatives were synthesized and purified by high-pressure liquid chromatography. Dehydration of 7,8-dihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene resulted in the formation of small amounts of 7-oxo-7,8,9,10-tetrahydrobenzoa[a]pyrene. A 7-keto species was also observed after similar treatment of the hydrocarbon-poly(G) hydrolysis products. Evidence of dehydration at the 9,10-positions was not observed. The hydrocarbon covalently bound to poly(G) is, therefore, a derivative of 7,8-dihydroxy-7,8,9,10-tetrahydrobenzol[a]pyrene with nucleic acid substitution at C-10 or 9.
On the obligatory role of the hypophysis in sexual differentiation hepatic metabolism in rats.
Authors: Gustafsson J A , Stenberg A
Published: May 2006

The hepatic metabolism of 4-[4-14C]androstene-3,17-dione and 5alpha-[4-14C]androstane-3alpha,17beta-diol was studies in castrated and hypophysectomized male rats with a transplanted pituitary under the kidney capsule. The effects of testosterone propionate and estradiol benzoate on liver metabolism were also studied in these experimental animals. It was found that the autonomous pituitary secreted a "feminizing factor" that transformed the male type of steroid metabolism characteristic of hypophysectomized rats into a female type of metabolism Hypophysectomized rats were unresponsive towards androgen action on the liver and did not respond with feminized hepatic metabolism after treatment with estradiol benzoate. It is concluded that estrogenic action on liver enzymes is mediated via modulation of the secretion of a central (probably hypothalamic) "feminizing factor inhibiting factor" and the sex hormonal effects of hepatic metabolism only occur in the presence of a pituitary in situ.
Functional genetic expression of eukaryotic DNA in Escherichia coli.
Authors: Struhl K , Cameron J R , Davis R W
Published: May 2006

We have isolated a segment of DNA from the eukaryote Saccharomyces cerevisiae (baker's yeast) as a viable molecular hybrid of bacteriophage lambda DNA which, when integrated into the chromosome of an E. coli histidine auxotroph, allows this bacterium to grow in the absence of histidine. The nonrevertable, histidine auxotroph lacks the enzymatic activity of imidazole glycerol phosphate (IGP) dehydratase (EC 4.2.1.19). From genetic experiments, we conclude that expression of the segment of yeast DNA results in the production of a diffusible substance and that transcription necessary for the complementation is most likely initiated from the segment of eukaryotic DNA.
An experiment eliminating the rotating carrier mechanism for the active transport of Ca ion in sarcoplasmic reticulum membranes.
Authors: Dutton A , Rees E D , Singer S J
Published: May 2006

An experiment has been carried out to test the rotating carrier mechanism of the translocation event in membrane transport. To the Ca-ATPase in intact sarcoplasmic reticulum membranes, 2,4-[3H]dinitrophenyl-cadaverine has been covalently attached by the action of the enzyme, transglutaminase. The binding of anti-2,4-dinitrophenyl antibodies to the 2,4-dinitrophenyl-modified membranes was found to have no effect on either the Ca-ATPase activity or the Ca ion transport rate of the membranes. These results rule out the rotating carrier mechanism in this system. A different scheme for the translocation process, the aggregate rearrangement mechanism, is discussed.
Ability of insulin to increase calcium binding by adipocyte plasma membranes.
Authors: McDonald J M , Bruns D E , Jarett L
Published: May 2006

Calcium specifically binds to adipocyte plasma membranes, demonstrating two classes of binding sites having affinity constants of 4.5 x 10(4) M-1 and 2.0 x 10(3) M-1. Insulin (100 microunits/ml) added directly to the isolated plasma membranes caused no alteration in calcium binding, whereas incubation of the adipocytes with 100 microunits/ml of insulin resulted in a 2.50 +/- 1.6% increase in calcium binding to the subsequently isolated plasma membranes. The increase in calcium binding produced by insulin resulted from an increase in the maximum binding capacities of both classes of binding sites without alteration in their affinity constants. Additionally, a second pool of calcium in adipocyte plasma membranes has been identified by atomic absorption analysis; it was more than two times larger than the maximum binding capacity of the calcium binding system. This pool of calcium was stable, did not participate in the 45Ca2+ exchange, and was unaltered by insulin treatment. A simialr stable pool of magnesium exists in plasma membranes and was also unaffected by insulin treatment. The increased capacity of the isolated plasma membranes to bind calcium after insulin treatment of the cells may represent an important bioregulating mechanism and supports the concept that calcium may play an important role in the effector system for insulin.
Control of cell division in Saccharomyces cerevisiae by methionyl-tRNA.
Authors: Unger M W , Hartwell L H
Published: May 2006

We suggest that two events are necessary for an asynchronous population of cells to undergo arrest in the GI phase of the cell cycle upon nutrient starvation. First, passage through GI must be prevented by a deficiency of some metabolic intermediate. Since this intermediate may act indirectly to arrest division, we designate it the "signal". We have found three conditions under which Saccharomyces cerevisiae cells arrest division in GI: sulfate starvation of a prototroph, methionine starvation of an auxotroph, or a shift of a conditional methionyl-tRNA synthetase mutant [L-methionine: tRNA Met ligase (AMP-forming), EC 6.1.1.10] to a restrictive condition. We interpret these results to indicate that the signal for sulfate starvation in S. cerevisiae is generated near the end of the sulfate assimilation pathway (at or beyond the formation of mehtionyl-tRNA). As a unifying hypothesis, we propose that the signal for all nutrients is generated at the level of protein biosynthesis.
New proposal for structure of special-pair chlorophyll
Authors: Shipman Lester L. , Cotton Therese M. , Norris James R. , Katz Joseph J.
Published: May 2006

A new model is proposed for the structure of the special pair of chlorophyll
a
molecules believed to correspond to the P700 species in green plants and algae. The proposed model, although admittedly speculative, is based upon exciton-theoretical considerations and on
in vitro
infrared and visible absorption spectra of a 700 nm absorbing ethanol adduct of chlorophyll
a
. In the new model, two chlorophyll
a
molecules are held together by (
a
) two strong ring V keto C[unk]O[unk]H[unk]O (or keto C[unk]O[unk]H[unk]N, or keto C[unk]O[unk]H[unk]S) hydrogen bonds and by (
b
) π-π van der Waals stacking interactions between the two chlorophyll
a
macrocycles. Macrocycle stacking provides the intermolecular π-π overlap necessary to promote the (experimentally observed) delocalization of the unpaired electron of the
in vivo
radical over two chlorophyll π systems. The new model provides an explicit role for the participation of protein in the formation of the chlorophyll special pair. The
in vitro
system yields an electron spin resonance signal indistinguishable from that of oxidized P700 in
Chlorella vulgaris
.
Kinetic theory and ergodic properties
Authors: Prigogine I. , Grecos A. P. , George Cl.
Published: May 2006

It is often assumed that the justification of kinetic theory lies in ergodic theory. From the properties of the collision operator, which plays a basic role in our kinetic description of dynamical systems, we show that this is not the case. We deduce that the asymptotic behavior of a class of states and observables is determined by the collisional invariants, independently of the ergodicity of the system. The relation between our conclusion and the stability concepts for classical Hamiltonian systems, introduced by Moser and others, is briefly indicated.
Altered penicillin-binding components in penicillin-resistant mutants of Bacillus subtilis.
Authors: Buchanan C E , Strominger J L
Published: May 2006

Penicillin- (cloxacillin-) resistant mutants of Bacillus subtilis were isolated in a stepwise fashion and the five penicillin-binding components (PBCs) in each were examined to determine which of the proteins, if any, corresponds to the penicillin killing site. PBCs II and V were previously eliminated as the likely penicillin targett. In the present work, PBC IV showed no change in sensitivity to cloxacillin in any of the resistant mutants isolated. PBC I did not change until the fifth-step mutant, in which it could not be detected by penicillin binding. Since PBC I did not bind penicillins that are lethal for this mutant, it also cannot be the lethal target. PBC II showed increased resistance to cloxacillin in three discrete steps, i.e., in mutants 1, 4, and 5, accompanied by changes in its electrophoretic mobility. However, the sensitivity of PBC II to penicillin G changed very little. Correspondingly, the cloxacillin-resistant mutants were unaltered in their sensitivity to penicillin G in vivo. Thus, of the five PBCs found in B. subtilis, PBC II is the most likely target for killing by penicillins.
Interrelationships between Ca2+ and adenylate and guanylate cyclases in the control of platelet secretion and aggregation.
Authors: Rodan G A , Feinstein M B
Published: May 2006

Ca2+ is a powerful inhibitor (Ki is congruent to 16 muM) of basal and prostaglandin E1 (PGE1)-stimulated adenylate cyclase [ATP pyrophosphate-lyase (cyclizing); EC 4.6.1.1] activity in membranes obtained from homogenized human platelets. Ca2+ (but not the ionophore A23,187) decreased V(max) of the reaction without an effect on the Ks for ATP. Neither ATP nor PGE1 affected Ki for Ca2+. In intact platelets A23,187 induced Ca2+ influx and markedly inhibited PGE1-stimulated rise in adenosine 3':5'-cyclic monophosphate (cAMP) levels. Guanylate cyclase [GTP pyrophosphate-lyase (cyclizing); EC 4.6.1.2] activity was mainly found in the soluble fraction (greater than 90%). Both soluble and membrane bound enzymes were stimulated by Mn2+ and Ca2+ and inhibited by Zn2+. Adenylate and guanylate cyclase activity were both present in a membrane fraction cyclase activity were both present in a membrane fraction which contained Ca2+ activated ATPase activity, and accumulated Ca2+ from the medium in the presence of ATP and oxalate. Other evidence indicates that these membranes originated in large part from the dense tubular system of the platelets. It is proposed that concurrent inhibition of adenylate cyclase and stimulation of guanylate cyclase facilitates the direct initiating effect of Ca2+ on platelet secretion and aggregation.
Structure of the prosthetic group of Klebsiella aerogenes citrate (pro-3S)-lyase.
Authors: Robinson J B , Singh M , Srere P A
Published: May 2006

The prosthetic group of citrate (pro-3S)-lyase [citrate oxaloacetate-lyase (pro-3S-CH2COO- leads to acetate); EC 4.1.3.6] from Klebsiella aerogenes was obtained by mild alkaline hydrolysis of the enzyme and purified by DEAE-cellulose chromatography. Several chemical and enzymatic degradation products of the compound have been isolated, and analyses of these have shown the structure of the prosthetic group to be 3'(or 2') leads to 1 inch-(5 inches-phosphoribosyl) dephosphocoenzyme A. Proof as to the exact linkage between the two ribose moieties and the anomeric configuration of the glycosidic bonds has not yet been obtained. A similar analysis was obtained for a product isolated after Pronase digestion of the enzyme (without alkaline hydrolysis). The isolated prosthetic group also can serve as a substrate for a crude preparation of acetate:-SH-(acyl carrier protein) enzyme ligase (AMP) from K. aerogenes, pure pig heart citrate (si)-synthase (EC 4.1.3.7), and pure rat liver ATP citrate (pro-3S)-lyase (EC4.1.3.8). This compound is the first shown to substitute for coenzyme A in the latter reaction.
Cell-free synthesis of rat preproinsulins: characterization and partial amino acid sequence determination.
Authors: Chan S J , Keim P , Steiner D F
Published: May 2006

Whole nucleic acid fractions of isolated rat islets of Langerhans greatly stimulate incorporation of radioactive amino acids into protein in a wheat germ ribosomal system. Approximately 30% of the synthetic product is precipitated with antisera to insulin or proinsulin. Characterization of this material by gel chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates a molecular mass of 11,500 daltons. Trypsin digestion releases intact A chain as well as tryptic fragments of the C-peptides and B chains of the two rat proinsulins. Automated sequence determination of labeled cell-free product purified by immunoprecipitation discloses the presence of 23 additional amino acids NH2-terminal to the B chain sequence of proinsulin. The partial amino acid sequence of this extension is as follows: NH2-X-Leu (Lys) Met-x-Phe-Leu-Phe-Leu-Leu (Lys) Leu-Leu-x-leu-X-X-X-X-X-X-X-X-proinsulin. On the basis of the above evidence we have designated this peptide preproinsulin.
Mapping of adenovirus messenger RNA by electron microscopy.
Authors: Westphal H , Meyer J , Maizel J V
Published: May 2006

Late adenovirus messenger RNA was annealed to complementary regions of partially melted viral double-stranded DNA. The RNA. DNA hybrid regions within the DNA molecules were visualized as loops in the electron microscope. Loops occurred at several regions of the DNA, most frequently, however, at a location near the center of the molecule. This hybridization technique appears well suited for an accurate mapping of messenger RNA, as well as for studies of RNA processing.
Size differences among immunoglobulin heavy chains from phosphorylcholine-binding proteins.
Authors: Rudikoff S , Potter M
Published: May 2006

The entire sequences of the heavy chain variable regions of M167 and TEPC 15 (phosphorylcholine-binding myeloma proteins of BALB/c origin) have been determined. These sequences are compared with the phosphorylcholine-binding protein M603. T15 differs from M603 at four positions, all of which are located in antigen-binding complementarity regions. M167, in addition to having differences in the complementarity regions, also has five substitutions in the conserved framework portion of the variable region when compared to T15 and M603. Each of the three proteins has a different length in the third complementarity region. It is unlikely that complementarity regions of different lengths associated with similar framework regions could be generated by proposed mechanisms of somatic mutation which are generally limited to point mutations. It appears more likely that these products are directly encoded by different structural germ line genes.
Monomer molecular weight of T antigen from simian virus 40-infected and transformed cells.
Authors: Carroll R B , Smith A E
Published: May 2006

T-antigens from simian virus 40 (SV 40)-transformed and lytically infected cells have been isolated by immunoprecipitation and their molecular weights estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. T-antigen from SV40-transformed mouse and hamster cells has an apparent molecular weight of 94,000 whereas that from several lines of SV40-infected monkey cells is 84,000. In a wheat germ cell-free system, mRNA from either transformed or productively infected cells is translated into a 94,000 species. Experiments with the protease inhibitors L-l-(tosylamide-2-phenyl)ethylchloromethyl ketone HCl and N-alpha-p-tosyl-L-lysylchloromethyl ketone HCl suggest that the 84,000 species of T-antigen found in infected cells is derived from the larger species by proteolytic cleavage. Further, the cleavage pathway probably involves a two-step reaction with an 89,000 intermediate. The biological significance of the two molecular weight forms of T-antigen is unknown, but the possibility that they have different physiological activities is discussed.
Metal-induced infidelity during DNA synthesis.
Authors: Sirover M A , Loeb L A
Published: May 2006

The effect of several divalent cations on the accuracy of DNA replication in vitro has been examined. Only Be2+ altered the accuracy of DNA synthesis using purified DNA polymerase (DNA nucleotidyltransferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase; EC 2.7.7.7) from avian myeloblastosis virus. The Be2+-induced base substitutions occurred with all templates and with all nucleotides tested. Analysis of the product by equilibrium density centrifugation and processive hydrolysis with snake venom phosphodiesterase suggested that the noncomplementary nucleotides were present in phosphodiester linkage. Nearest neighbor studies indicated that many of the Be2+-induced errors were present as single base substitutions. The enhancement of error frequency could be duplicated by the pretreatment of the enzyme, but not the template, with Be2+. Glycerol gradient centrifugation dissociated the Be2+-DNA polymerase complex and restored the initial error frequency of the polymerase. Thus, the weak binding of a metal cation to a DNA polymerase could alter the accuracy with which that polymerase copied DNA. Beryllium is a known carcinogen. The potential use of this system as a screening technique to detect chemical mutagens and carcinogens is considered.
The evolution of a universal genetic code
Authors: Wong J. Tze-Fei
Published: May 2006

Some of the basic problems presented by the rapid evolution of a universal genetic code can be resolved by a mechanism of co-evolution of the code and the amino acids it serves.
Role of a peptidase in phagocyte chemotaxis.
Authors: Aswanikumar S , Schiffmann E , Corcoran B A , Wahl S M
Published: May 2006

The potencies of N-formylmethionyl (fMet) peptides as chemotactic agents for phagocytes are related to the rates at which they are hydrolyzed. Furthermore, chloromethyl ketones inhibit chemotaxis as do the products of hydrolysis of fMet peptides. The directed migration of cells in response to such peptides is probably brought about by the binding of the peptide to a cell receptor with subsequent cleavage by peptidase specific for aromatic residues, a process that allows the chemical gradient to be detected.
Direct spectroscopic observation of inner and outer hydrocarbon chains of lipid bilayer vesicles.
Authors: Longmuir K J , Dahlquist F W
Published: May 2006

Distearoylphosphatidylcholines labeled with gem-difluoro groups at selected positions of the fatty acid chains have been prepared. These lipids were incorporated into sonicated vesicles and were examined by fluorine nuclear magnetic resonance spectroscopy. All spectra are characterized by two well-separated fluorine resonances. Paramagnetic ions added to the exterior solution of vesicles of fluorinated lipid broaden the upfield resonances, whereas ions trapped in the vesicles interior broaden the downfield resonances. This demonstrates that the fluorine chemical shift of these compounds is sensitive to differences between the inner and outer monolayers of sonicated vesicles.
Experimental examination of the “energy upconversion” theory for green plant photosynthesis
Authors: Warden Joseph T.
Published: May 2006

Spinach chloroplasts, dark adapted for periods of three days to three months, yield P700
+
formation (electron spin resonance signal 1) on the first as well as the following flashes in an actinic series of xenon light flashes of 10 μs duration. These data are in contradiction with the prediction of the “energy upconversion” theory [F. K. Fong (1975)
Appl. Phys.
6, 151-156] that only the second flash would be effective.
Organization and energy-dependent growth of microtubules in cells.
Authors: Frankel F R
Published: May 2006

The organization and growth of microtubules in cultured mouse macrophages and fibroblasts were examined by indirect immunofluorescence microscopy with antibodies to microtubule protein. In macrophages, microtubules converged at a samll region at the cytocenter. During depolymerization, and repolymerization, this region acted as a microtubule organizing center. Microtubule growth was energy-dependent, but unaffected by dibutyryl-adenosine 3':5'-cyclic monophosphate, cholera toxin, or dibutyryl-guanosine 3':5'-cyclic monophosphate. Fibroblasts, which did not show such a simple microtubule organization as macrophages, contained mainly one or two, but occasionally as many as four, organizing centers during repolymerization. These microtubule organizing centers often appeared as fluorescent rings with a dark center.
Vitamin K-dependent synthesis and modification of precursor prothrombin in cultured H-35 hepatoma cells.
Authors: Munns T W , Johnston M F , Liszewski M K , Olson R E
Published: May 2006

The ability of confluent monolayers of H-35 cells, originally obtained from a rat hepatoma, to synthesize prothrombin in response to vitamin K1 (phylloquinone) was studied. As demonstrated by radioimmunoassay, selective barium salt adsorption, and two coagulation assays which discriminate between precursor- and mature-prothrombin, these cells retained their ability to synthesize precursor prothrombin (preprothrombin) in the absence of exogenous phylloquinone (vitamin K). When phylloquinone was added to the medium (100 ng/ml), the existing intracellular concentration of preprothrombin was reduced to 50% within 1 hr after exposure to the vitamin and slowly declined thereafter to approximately 30% of control levels by 36 hr. Concomitant with the rapid loss of intracellular preprothrombin was the appearance of mature prothrombin in the medium. The appearance of prothrombin was biphasic: occurring during the initial 0-6 hr interval, and again at an increased rate during the next 18-24 hr interval. The amount of prothrombin appearing in the medium exceeded by severalfold the amount of precursor mobilized. These data demonstrate that monolayer cultures of H-35 hepatoma cells retain their ability to synthesize preprothrombin and other enzymes, responsible for post-translational modification of prothrombin and its subsequent secretion, under the influence of vitamin K.
Quantitation of delta-crystallin messenger RNA during lens induction in chick embryos.
Authors: Shinohara T , Piatigorsky J
Published: May 2006

Embryonic chick cells of the presumptive lens ectoderm are induced to differentiate into a lens by the optic vesicle, an outgrowth from the developing brain. This lens induction involves formation of the lens placode by cell elongation between about 44 and 50 hr of development, followed by invagination of the placode between about 50 and 55 hr of development. The amount of delta-crystallin messenger RNA (mRNA) in heads of embryos between 48 and 72 hr of development was determined by molecular hybridization with [3H]DNA complementary to purified delta-crystallin mRNA. An average of approximately 0.5 pg of delta-crystallin mRNA was found per embryonic head at 48 hr of development. This leads to approximately 265 molecules of delta-crystallin mRNA per lens cell, if one assumes that the mRNA is confined to the lens rudiment, as is indicated by immunofluorescence studies of delta-crystallin performed by other investigators. Pulse-labeling experiments with [35S]methionine indicated that the delta-crystallin mRNA is being translated already at this time. delta-Crystallin mRNA accumulated at an average rate of 1 molecule per cell per minute between 48 and 72 hr of development. Thus, by extrapolation, the initiation of delta-crystallin mRNA accumulation coincides with the initiation of lens placode formation at approximately 43-44 hr of development, which is some 8-9 hr after the initiation of lens induction by the optic vesicle. These data suggest that delta-crystallin synthesis is regulated by the accumulation of delta-crystallin mRNA during lens induction in chick embryos.
Polycation-induced assembly of purified tubulin.
Authors: Erickson H P , Voter W A
Published: May 2006

Several different polycations have been found that can substitute for the microtubule-associated proteins, or tau factor, in facilitating assembly of tubulin that has been purified by ion exchange chromatography. In low concentrations of the polycation diethylaminoethyl-dextran, 7 mg of tubulin is pelleted per 1 mg of polycation added. Under conditions favorable to microtubule assembly the entire pellet is seen by electron microscopy to consist of "double wall microtubules", which are essentially identical to normal microtubules in subunit structure and arrangement. When assembly is inhibited approximately the same amount of tubulin is pelleted, but it is in the form of clusters of curved sheets or filaments apparently related to tubulin rings. When conditions are changed to favor assembly, the tubulin within these clusters appears to reassemble to form the double wall microtubules.
Freeze-fracture study of mast cell secretion.
Authors: Chi E Y , Lagunoff D , Koehler J K
Published: May 2006

Within seconds after exposure of rat peritoneal mast cells to polymyxin B, bulges appear on the surface of the cells. Freeze-fracture electron microscopy reveals that each bulge overlies a mast cell granule. In contrast to the even distribution of intramembranous particles in the plasma membrane of unstimulated cells, the intramembranous particles in the stimulated cells are unevenly distributed in the membrane of the bulges with large patches of membrane lacking intramembranous particles. The membranes over the most prominent bulges are entirely free of intramembranous particles, and in some instances there is an increased concentration of intramembranous particles at the margins of the bulges. Perigranule membranes exhibit the same changes in distribution of intramembranous particles. Electron microscopy of thin sections of rapidly fixed, stimulated mast cells shows a peculiar structure of the membrane overlying some bulges; instead of the pentalaminar membranes previously demonstrated, the membrane at these sites of presumptive fusion of perigranule and plasma membrane assumes the form of a single dense lamina with a fine fuzzy coating on either side. It seems possible that membrane fusion and subsequent pore formation proceed in the stimulated mast cell through a stage of flight of intramembranous particles and molecular rearrangement of the other membrane components.