bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of hemoglobin AIc in normal and diabetic mice: potential model of basement membrane thickening.
Authors: Koenig R J , Cerami A
Published: May 2006

Adult diabetic mice (C57Bl/KsJ--db/db) have increased amounts of a minor hemoglobin in their peripheral blood compared to wild-type (+/+) mice. This increase is analogous to the 2-fold increase of a glycohemoglobin with similar chromatographic mobility (Hb AIc) seen in the blood of patients with diabetes mellitus. Although the exact chemical nature of human or mouse Hb AIc is unknown, both contain a sodium-borohydride-reducible linkage on the beta chain which is a presumed Schiff base between a sugar moiety and the protein. The db/db animals, which have normal amounts of mouse Hb AIc at weaning, show the increase approximately 4 weeks after the onset of the signs of diabetes. This rise is brought about by an increase in a circulating factor that determines directly or indirectly the synthesis of mouse Hb AIc as a post-synthetic modification of Hb A. Evidence for this was obtained by showing that the rate of synthesis of the modified Hb is linear for at least the first 50 days of the life of the red cell and that the rate of synthesis is dependent on the environment in which the cells circulate. Thus the rate of mouse Hb AIc synthesis in +/+ cells is greater when those cells circulate in a db/db host than when they circulate in a +/+ host. The nature of the humoral factor is unknown. If glycosylations of basement membrane proteins and hemoglobin proceed via a common mechanism, then the monitoring of Hb AIc could provide a useful model for studying the early events of basement membrane thickening.
Mating signal and DNA penetration deficiency in conjugation between male Escherichia coli and minicells.
Authors: Ou J T
Published: May 2006

Strain OU122, a dnaB mutant of HfrH which stops vegetative DNA synthesis immediately when the temperature is shifted to 43 degrees, was mated at 43 degrees with minicells with and without 1 mM Zn2+. Synthesis of DNA was detected in the mating mixture containing minicells derived from either Fchi925 or F+chi115 cells, but only a small amount was detected in the mixture containing 1 mM Zn2+ which inhibits the formation of mates (previously called mating pairs). The supernatant liquid from cell cultures did not induce DNA synthesis, suggesting that DNA synthesis was not stimulated by diffusible molecules. Additional experiments showed that Zn2+ inhibited DNA synthesis associated with DNA transfer but did not inhibit the DNA transfer that had already been initiated. Thus, the stimulation of DNA synthesis observed required physical interaction of cells and F pili. Reisolated minicell exconjugants derived from the cross OU122 X F--chi925 minicells were shown to contain transferred DNA in contrast to either the cross OU122 X F--chi925 minicells in 1 mM Zn2+, or the cross OU122 X F+chi1115 minicells. Thus, F+chi1115 minicells retained the property of surface exclusion at 43 degrees.
Rapid-flow resonance Raman spectroscopy of photolabile molecules: rhodopsin and isorhodopsin.
Authors: Mathies R , Oseroff A R , Stryer L
Published: May 2006

We have devised a method for obtaining the resonance Raman spectrum of a photolabile molecule before it is modified by light. The essence of this technique is that the sample is flowed through the light beam at a sufficiently high velocity so that the fraction of photoisomerized (or photodestroyed) molecules in the illuminated volume is very low. This rapid-flow technique has enabled us to measure the resonance Raman spectrum of unphotolyzed bovine rhodopsin in Ammonyx LO detergent solution and in sonicated retinal disc membranes. The major features of these spectra, which are very similar to one another, are the protonated Schiff base line near 1660 cm-1, the ethylenic line at 1545 cm-1, lines due to skeletal modes at 1216, 1240, and 1270 cm-1, and a line due to C-H bending at 971 cm-1. The resonance Raman spectrum of unphotolyzed isorhodopsin formed by the addition of 9-cis-retinal to opsin was also measured. The spectrum of isorhodopsin is more complex and differs markedly from that of rhodopsin. In isorhodopsin, the ethylenic line is shifted to 1550 cm-1, and there are six lines between 1153 and 1318 cm-1. The rapid-flow technique described here makes it feasible to control the extent of interaction between light and any photolabile molecule. We present a theory for predicting the effective sample composition in the illuminated volume as a function of the flow rate, light intensity, and spectral characteristics of the photolabile species.
Induction of human fibroblast proliferation by epidermal growth factor (EGF): enhancement by an EGF-binding arginine esterase and by ascorbate.
Authors: Lembach K J
Published: May 2006

The effect of mouse epidermal growth factor (mEGF) and an mEGF-binding arginine esterase on the growth of cultured human fibroblasts has been studied. Physiological concentrations (10(-9)-10(-10) M) of the growth factor were found to stimulate DNA replication and cell proliferation in quiescent cultures, and the arginine esterase, which is normally associated with mEGF in vivo, was shown to enhance this growth effect synergistically. The cellular response to mEGF was dependent upon a low, growth-limiting concentration of serum in the extracellular medium. Ascorbic acid, which alone exhibited no growth-promoting effect, could partially replace this requirement, and was found to elicit a rapid and marked increase in proline hydroxylation. Quiescent cultures in serum-free medium containing ascorbic acid were stimulated by the combination of mEGF and the esterase in a manner comparable to that achieved with serum shift-up. The possible requirement of a collagen-containing extracellular matrix for the growth response to mEGF is discussed.
Inhibition of initiation of protein synthesis by 7-methylguanosine-5'-monophosphate.
Authors: Hickey E D , Weber L A , Baglioni C
Published: May 2006

Translation of rabbit globin mRNA in a wheat germ protein-synthesizing system is inhibited by the nucleotide 7-methylguanosine-5'-monophosphate (m7G5'p) but not by other guanosine nucleotides without the 7-methyl group or with the phosphate in a different position. Translation of RNA of tobacco mosaic virus and poly(A) + HeLa RNA is also inhibited by m7G5'p. We show that m7G5'p prevents the association of mRNA with ribosomal subunits to form an initiation complex. We propose that m7G5'p interacts with a site on initiation factor(s) or ribosomes which is involved in mRNA recognition, presumably by binding to the 5'-terminal sequence m7G5'ppp. m7G5'p does not inhibit translation of poly(U) and RNA of satellite tobacco necrosis virus, which do not have the 5'-terminal sequence m7G5'ppp. In the case of RNA of satellite tobacco necrosis virus, some stimulation of its translation is consistently observed in the presence of m7G5'p; possible interpretations of this finding are discussed.
Genetics of somatic mammalian cells: genetic, immunologic, and biochemical analysis with Chinese hamster cell hybrids containing selected human chromosomes.
Authors: Kao F T , Jones C , Puck T T
Published: May 2006

Through hybridization of specific Chinese hamster cell auxotrophs with human cells and selection in media lacking the nutritional supplements required by the former cells, a series of stable hybrid clones can be prepared. These hybrids have genomes consisting of a common part--the complete or almost complete set of Chinese hamster chromosomes, plus a variable part--one or a few human chromosomes. The identity of the human chromosomes can be varied by utilizing different Chinese hamster auxotrophs and the appropriate selective media. The human chromosomes present can be determined by a combination of cytogenetic analysis with chromosome banding and testing for specific human marker genes. Hybrids containing single human chromosomes 11 and 12 and the combination of both 11 and 12 are described. The system appears to lend itself to various studies such as identification of human cell surface antigens, determination of their chromosomal loci, measurement of their distribution among cells of normal human tissues, study of interrelations among syntenic and asyntenic genes, and mutational analysis of the human genome.
Serial propagation of Creutzfeldt-Jakob disease in guinea pigs.
Authors: Manuelidis E E , Kim J , Angelo J N , Manuelidis L
Published: May 2006

The transmission and serial propagation of Creutzfeldt-Jakob disease from man to guinea pigs are reported. The latency, symptomatology, and morphology of the infection during the first four passages are presented. The incubation period between the first and subsequent passages was halved. One hundred percent take, morbidity, and mortality were achieved in all inoculated animals. All guinea pigs developed a subacute spongiform virus encephalopathy with marked neuronal destruction in the cerebral cortex and subcortical grey structures. The neuronal loss resulted in cerebral atrophy and hydrocephalus ex vacuo.
Carcinogenicity of benzo[a]pyrene 4,5-, 7,8-, and 9,10-oxides on mouse skin.
Authors: Levin W , Wood A W , Yagi H , Dansette P M , Jerina D M , Conney A H
Published: May 2006

Benzo[a]pyrene and three arene oxides of benzo[a]pyrene (benzo[a]pyrene 4,5-, 7,8-, and 9,10-oxides) have been tested for carcinogenicity in mice by topical application of each compound (0.1 or 0.4 mumol) once every 2 weeks for 60 weeks. At the high dose, benzo[a]pyrene and the 7,8-oxide were highly carcinogenic, whereas the 4,5-oxide (K-region oxide) was weakly active and the 9,10-oxide was inactive. At the low dose, only benzo[a]pyrene was highly carcinogenic. The carcinogenic activities of the three arene oxides of benzo[a]pyrene were not correlated with their stabilities or mutagenic activities.
Darwin's finches: population variation and natural selection.
Authors: Grant P R , Grant B R , Smith J N , Abbott I J , Abbott L K
Published: May 2006

Van Valen's model, which relates morphological variation to ecological variation in an adaptive scheme, was investigated with individually marked and measured Darwin's finches on two adjacent Galápagos islands, Santa Cruz and Daphne Major. Results show that environmental heterogeneity is correlated with large continuous, morphological variation: variation in bill dimensions of Geospiza fortis is greater on Santa Cruz than on Daphne, as is environmental heterogeneity. Within populations of this species, different phenotypes distribute themselves in different habitat patches, select foods of different sizes and hardness, and exploit them with efficiencies that are phenotype- (bill size) dependent. These data constitute indirect evidence that natural selection has a controlling influence over the level of phenotypic variation exhibited by a population. Further evidence is that phenotypes did not survive equally well during the study period; on Daphne island G. fortis was apparently subjected to directional selection on bill tip length and G. scandens to normalizing selection on body weight and bill depth. Other factors which may have contributed to the establishment of a difference in variation between Santa Cruz and Daphne populations are the founder effect, genetic drift, and assortative mating. Annual climatic unpredictability is considered a source of environmental heterogeneity which, through its effect upon food supply, favors large morphological variation. It is predicted that species of large individual size are more influenced by this than are small species, and consequently exhibit greater size-corrected variation. The prediction is tested with data from six Geospiza species, and found to be correct.
A ribosome-dependent GTPase from yeast distinct from elongation factor 2.
Authors: Skogerson L , Wakatama E
Published: May 2006

Three proteins required for poly(U)-directed polyphenylalanine synthesis have been separated from yeast. Two of the factors correspond to the elongation factors 1 and 2 described for other eukaryotic systems, according to the criteria of phenylalanyl-tRNA binding and diphtheria toxin-catalyzed ADP-ribosylation. The third protein, while absolutely required for polyphenylalanine synthesis, was a more active ribosome-dependent GTPase than elongation factor 2.
Identification of nonhistone chromatin proteins in chromatin subunits.
Authors: Liew C C , Chan P K
Published: May 2006

Rat liver chromatin was digested by micrococcal nuclease. More than 80% of the enzyme-digested chromatin could be recovered after centrifugation. Treatment with sodium deoxycholate and Triton X-100 at concentrations of 0.5% in the final chromatin suspension gave a higher recovery. Chromatin subunits were fractionated on a 5-30% linear sucrose density gradient. Approximately 35% of the chromatin subunits could be recovered from the gradient. Chromatin subunits and their DNA fragments were identified by gel electrophoresis and ultracentrifugation. The presence of nonhistone chromatin proteins (NHCP) in chromatin subunits was demonstrated by the following criteria: (i) Quantitative analysis showed that the mass ratio of histone to NHCP, in the presence or absence of detergents, was 1:0,25 or 1:0.1, respectively. (ii) After the removal of acid-soluble protein from the subunits, it was found that most of the phenol-soluble NHCP were similar to total chromatin NHCP. However, four major fractions of these phenol-soluble NHCP were found to be enriched in the subunits as identified by two-dimensional polyacrylamide gel electrophoresis. (iii) Experiments using an exchange of isotope-labeled and nonlabeled chromatin showed that NHCP were tightly bound to the chromatin subunits.
On the specificity of synapse formation.
Authors: Puro D G , Nirenberg M
Published: May 2006

Clonal neuroblastome X glioma hybrid cells form synapses with striated muscle cells from different muscles and from different organisms, such as chick, mouse, and rat. Under appropriate conditions 65-80% of the muscle cells exhibited synaptic responses. The results indicate that most striated muscle cells have the same specificity for synapse formation and suggest that synaptogenesis is not dependent on interactions between complementary molecules on neuron and muscle cells that code for different synaptic connections.
Rous-sarcoma-virus-transformed fibroblasts having low levels of plasminogen activator.
Authors: Wolf B A , Goldberg A R
Published: May 2006

Several clones of transformed chick embryo fibroblasts infected with wild-type B77-C or Prague-C strain of Rous sarcoma virus have been isolated from soft agar suspension. These clones were screened for plasminogen activator activity by overlaying monolayer cultures with medium containing agar, casein, and chicken plasminogen. Twenty-three percent of all of the isolated clones showed little caseinolytic activity, 42% had intermediate activity, and 35% had high activity. Although the clones with low plasminogen activator activity had no more than twice the activity shown by uninfected fibroblasts, they did not differ significantly from clones possessing high levels of plasminogen activator in their morphology, 2-deoxyglucose transport, or efficiency of colony formation in soft-agar.
Opiate receptor: autoradiographic localization in rat brain.
Authors: Pert C B , Kuhar M J , Snyder S H
Published: May 2006

Opiate receptor sites in rat brain can be labeled in vivo by [3H]diprenorphine, a potent opiate antagoinst. Using techniques to minimize diffusion in fresh, frozen, unfixed brain, we have localized [3H]diprenorphine by autoradiography to visualize the distribution of opiate receptors. Silver grains indicative of the binding of labeled [3H]diprenorphine are discretely localized in numerous areas of the brain with very high densities in the locus coeruleus, the substantia gelatinosa of the spinal cord, and in clusters within the caudate-putamen, amygdala, and parts of the periventricular gray matter.
Resonance enhanced coherent anti-Stokes Raman scattering.
Authors: Hudson B , Hetherington W , Cramer S , Chabay I , Klauminzer G K
Published: May 2006

Resonance enhancement of coherent anti-Stokes Raman scattering due to the proximity of the laser frequencies to an electronic transition has been demonstrated for dilute solutions of diphenyloctatetrane in benzene. The Raman contribution to the third order susceptibility is shown to be complex near an electronic resonance and the resulting features of the coherent anti-Stokes Raman scattering spectra are discussed in detail. This work represents one step in the demonstration that the high signal to noise ratio, fluorescence rejection, and low average power levels of the coherent anti-Stokes Raman scattering experiment can be used to advantage in Raman studies of dilute solutions and materials of biological interest.
Crystal structure of a complex between lumiflavin and 2,6-diamino-9-ethylpurine: a flavin adenine dinucleotide model exhibiting charge-transfer interactions.
Authors: Scarbrough F E , Shieh H , Voet D
Published: May 2006

The x-ray structure of the deep red crystalline complex lumiflavin-2,6-diamino-9-ethylpurine has been determined. The flavin and adenine derivatives form hydrogen-bonded base pairs of the Watson-Crick type. The molecules in the crystal also associate via extensively overlapped flavin/adenine and flavin/flavin stacking interactions in which there are several contacts that are closer than van der Waals distances. This, together with the red color of the crystals, is indicative of the formation of a charge-transfer complex.
(+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo (a)pyrene: a potent skin carcinogen when applied topically to mice.
Authors: Levin W , Wood A W , Yagi H , Jerina D M , Conney A H
Published: May 2006

(+/-)-trans-7,8-Dihydroxy-7,8-dihydrobenzo[a]-pyrene, a known metabolite of benzo [a]pyrene, has been tested for carcinogenic activity on mouse skin by topical application of 0.15 or 0.30 mumol every 2 weeks for 60 weeks. At the low dose (0.15 mumol), the compound was equipotent to the parent hydrocarbon, benzo[a]pyrene, and considerably more potent than its metabolic precursor, benzo[a]pyrene 7,8-oxide, in eliciting tumors, as determined by both the onset of tumors and the total number of animals developing carcinomas. Application of 7,8-epoxy-,8,9,10-tetrahydrobenzo[a]pyrene (0.30 mumol every 2 weeks), a compound related to the carcinogenic benzo[a]pyrene 7,8-oxide but with the double bond removed from the 9,10-position of the molecule, did not elicit any tumors. The above results indicate that the (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene is a more proximate carcinogen than benzo[a]pyrene 7,8-oxide and that the carcinogenicity of benzo[a]pyrene 7,8-oxide and (+/-)trans-7,8-digydrobenzo[a]pyrene may be due to metabolic conversion of these compounds to the highly reactive and mutagenic stereoisomers of 7,8-digydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene.
Actin-like filaments amd membrane rearrangement in oxyntic cells.
Authors: Vial J D , Garrido J
Published: May 2006

The secretory pole of vertebrate oxyntic cells possesses two distinct membrane systems: the apical plasma membrane which presents numerous infoldings, microvilli and processes, and a complex tubulovesicular system located in close proximity to the plasma membrane. These two membrane systems are generally believed to be interconvertible in relation to the functional state of the cell. To determine the role that filaments may play in the interconversion process, the secretory pole of rat and toad oxyntic cells was examined by electron microscopy under conditions designed to demonstrate filamentous structures, i.e., slight cellular swelling and incubation with heavy meromyosin. Filaments 50-80 A in diameter are present in close association with the plasma membrane to which they are connected by regularly spaced bridges. Heavy meroxyosin-treated material reveals "decorated" filaments in topographically corresponding locations. No filaments are seen in association with membranes of the tubulovesicular system. These findings suggest that association with actin-like filaments is a step in the translocation of membranes from the tubulovesicular system to the plasma membrane.
Differential labeling of the cell surface of single ciliary ganglion neurons in vitro.
Authors: Wessells N K , Nuttall R P , Wrenn J T , Johnson S
Published: May 2006

Cationic ferritin binds in a time and concentration dependent manner to all surfaces of ciliary ganglion neurons in culture except "mounds" and "veils". In chase experiments, bound ferritin clears from the cells surfaces and forms larger and larger patches, even at low temperatures. Binding of cationic ferritin is inhibited by poly-L-lysine, potentiated by poly-L-glutamate, and not affected by neruaminidase (acylneuraminyl hydrolase, EC 3.2.1.18), hyaluronidase (hyaluronoglucosidase, hyaluronate 4-glycanhydrolase, EC 3.2.1.35), or chondroitin ABC lyase (EC 4.2.2.4).
Genetic controls of meiotic recombination and somatic DNA metabolism in Drosophila melanogaster.
Authors: Baker B S , Boyd J B , Carpenter A T , Green M M , Nguyen T D , Ripoll P , Smith P D
Published: May 2006

Recombination-defective meiotic mutants and mutagen-sensitive mutants of D. melanogaster have been examined for their effects on meiotic chromosome behavior, sensitivity to killing by mutagens, somatic chromosome integrity, and DNA repair processes. Several loci have been identified that specify functions that are necessary for both meiotic recombination and DNA repair processes, whereas mutants at combination and DNA repair processes, whereas mutants at other loci appear to be defective in only one pathway of DNA processing.
The opiate receptor: a model explaining structure-activity relationships of opiate agonists and antagonists.
Authors: Feinberg A P , Creese I , Snyder S H
Published: May 2006

A model of the opiate receptor is proposed which explains structure-activity relationships of opiate drugs, including (i) the unique potency of certain opiates such as etonitazene, fentanyl, phenazocine, and oripavines; (ii) the role of N-allyl substituents in conferring antagonist properties; and (iii) chemical features that afford "pure" antagonists. The model indicates mlecular mechanisms for interconversion of the opiate receptor between respective states that bind agonists or antagonists with high affinity.
Relation between oxidative metabolism and slow rhythmic potentials in mammalian intestinal muscle.
Authors: Connor J A , Kreulen D L , Prosser C L
Published: May 2006

Intact muscle layers separated from the small intestine of the cat were mounted in a specially designed chamber to measure electrical slow waves and NADH fluorescence simultaneously. Cooling the muscle to 17 degrees eliminated slow waves and simultaneously increased the level of fluorescence. Likewise, superfusing the muscle with a N2-bubbled glucose-free Krebs solution decreased the amplitude of slow waves and concomitantly increased fluorescence emission. In both cases, return to normal conditions reversed the effects on both slow waves and fluorescence. When signals were averaged over 30-70 slow waves, a pattern emerged with the fluorescence oscillations in phase with the electric oscillations. The NADH:NAD+ ratio reached a maximum at the most depolarized point of the slow waves and a minimum at the most polarized point between slow waves. This indicates maximum ATP utilization during the repolarization process. The correlation between redox oscillations and electrical slow wave generation is associated with cell metabolism.
Metal clusters in catalysis: Hydrocarbon reactions
Authors: Caulton K. G. , Thomas M. G. , Sosinsky B. A. , Muetterties E. L.
Published: May 2006

A set of metal carbonyl clusters, Ru
3
(CO)
12
, Os
3
(CO)
12
, and Ir
4
(CO)
12
, has been evaluated as catalysts for a series of hydrocarbon reactions which comprise skeletal rearrangement, metathesis, dehydrogenation, hydrogenation, isomerization, and H-D exchange. None was especially effective as a hydrogenation catalyst even for olefins. Os
3
(CO)
12
was a catalyst for H-D exchange between C
6
H
6
and D
2
at 195° but the ruthenium congener was inactive at temperatures below 175°, a temperature where ruthenium metal formed at an appreciable rate. Deuterium incorporation in the benzene was a single-step process. Ir
4
(CO)
12
was an effective catalyst for the conversion of cyclohexadiene to cyclohexene and benzene. A similar reaction occurred with cyclohexene but the rate was extremely low at 160°. The ruthenium and osmium clusters catalyzed the isomerization of linear hexenes, with the former the more active. Relative rates for the hexenes were 1 > 2 > 3. At high temperatures, the osmium and iridium clusters catalyzed skeletal reactions of 2-hexene, as evidenced by the formation of pentenes, heptenes, heptanes, and small amounts of propane.
Maximal functions associated to smooth curves
Authors: Stein E. M. , Wainger S.
Published: May 2006

Let
t
→ γ(
t
), 0 ≤
t
≤ 1, be a smooth curve in IR

n

. Define the maximal function [unk](
f
) by [unk](
f
)(
x
) = sup

0<
h
≤1

(1/h) ʃ
0
h
ǀ
f
(
x
- γ(
t
))ǀ
dt
. We state conditions under which ∥[unk](
f
)∥

p

≤

A
p

∥
f
∥

p

, for 1 <
p
≤ ∞.
Isolation of 3-phosphohistidine from phosphorylated pyruvate, phosphate dikinase.
Authors: Spronk A M , Yoshida H , Wood H G
Published: May 2006

Pyruvate, phosphate dikinase (EC 2-7-9-1) catalyzes formation of phosphoenolpyruvate, AMP, and inorganic pyrophosphate from pyruvate, ATP, and orthophosphate. A pyrophosphoryl and phosphoryl form of the enzyme is involved in this transfer. The [32P]phosphoryl form of pyruvate, phosphate dikinase was prepared with enzyme isolated from Bacteroides symbiosus. The [32P]phosphoryl enzyme was found to have properties corresponding to a phosphoramidate linkage and this was confirmed by isolation of 3-[32P]phosphohistidine from alkaline hydrolysates of the enzyme. The histidyl residue is considered to be the pyrophosphoryl- and phosphoryl-carrier between the three substrate sites of this enzyme.
Photoaffinity site-specific covalent labeling of human corticosteroid-binding globulin.
Authors: Marver D , Chiu W , Wolff M E , Edelman I S
Published: May 2006

A method was developed for the synthesis of high-specific-activity 21-diazo-21-[6,7-(3)H]deoxycorticosterone, an analog of corticosterone. This analog was used as a photoaffinity label of a high affinity steroid-binding protein, human corticosteroid-binding globulin. Based on direct binding studies and crosscompetition experiments, this diazo derivative exhibited the requisite affinity (within a factor of 1.5 times that of corticosterone) and site specificity to qualify as an affinity labeling legand. Irradiation of corticosteroid-binding globulin with the 21-diazo derivative resulted in irreversible binding to corticosteroid-binding globulin, identified by polyacrylamide gel electrophoresis. Specificity of covalent binding to corticosteroid-binding globulin was established by competition analysis with various steroids. Irreversibility of photodependent binding was shown by persistence of the complex on electrophoresis (in contrast to the noncovalently linked complex), and resistance to exchange with corticosterone or pregnanediol and to solvent extraction. Site specificity of covalent binding was inferred from the effects of a scavenger, Tris-HC1, and fluorescence quenching of a neighboring tryptophan.
Novobiocin and coumermycin inhibit DNA supercoiling catalyzed by DNA gyrase.
Authors: Gellert M , O'Dea M H , Itoh T , Tomizawa J
Published: May 2006

Novobiocin and coumermycin are known to inhibit the replication of DNA iing of DNA catalyzed by E. coli DNA gyrase, a recently discovered enzyme that introduces negative superhelical turns into covalently circular DNA. The activity of DNA gyrase purified from a coumermycin-resistant mutant strain is resistant to both drugs. The inhibition by novobiocin of colicin E1 plasmid DNA replication in a cell-free system is partially relieved by adding resistant DNA gyrase. Both in the case of coliclls. DNA molecules which are converted to the covalently circular form in thepresence of coumermycin remain relaxed, instead of achieving their normal supercoiled conformation. We conclude that DNA gyrase controls the supercoiling of DNA in E. coli.
An 18,000 molecular weight polypeptide induces early events and stimulates DNA synthesis in cultured cells.
Authors: Bourne H R , Rozengurt E
Published: May 2006

Extracts of serum-free medium, conditioned by contact with SV40-transformed BHK cells, stimulate DNA synthesis in cultured fibroblasts. From this source, we have purified a homogenous basic protein of 18,000 molecular weight, termed fibroblast derived growth factor. In submicrogram quantities, fibroblast derived growth factor stimulates DNA synthesis in mouse 3T3 cells, in the absence of added serum. Prior to the onset of DNA synthesis, both serum and fibroblast derived growth factor induce an array of nearly simultaneous biochemical changes in the membrane to 3T3 cells that include stimulation of the uptake of nucleosides, 2-deoxyglucose, and 86Rb+. These results strongly suggest that the early events are integral components of the proliferative response, rather than coincidental effects of nonmitogenic molecules present in serum.
Bvr-1, a restriction locus of a type C RNA virus in the feline cellular genome: identification, location, and phenotypic characterization in cat X mouse somatic cell hybrids.
Authors: O'Brien S J
Published: May 2006

Somatic cell hybrids were constructed between BALB/c-RAG mouse cells and feline lymphoma cells by the hypoxanthine-aminopterin-thymidine selection scheme. RAG cells spontaneously produce an endogenous B-tropic type C virus. Cat-mouse hybrids preferentially segregate feline chromosomes and retain murine chromosomes-demonstrable by karyotypic and isozyme analyses. Despite the presence of the complete mouse genome, including the viral genome, virus production was diminished to 1-5% of the levels observed in RAG parents based upon particle-associated RNA-dependent DNA polymerase (reverse transcriptase) activity in the culture fluid. Thirty-seven hybrids made on four different occasions had suppressed virus levels, and no hybrids expressed parental virus levels. Reverse selection experiments on 6-thioguanine demonstrated that a restriction gene, tentatively named Bvr-1, was linked to the feline structural genes for hypoxanthine phosphoribosyltransferase (IMP:pyrophosphate phosphoribosyltransferase; EC 2.4.4.8) and glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP+ 1-oxidoreductase; EC 1.1.1.49) in cats, probably on the X-chromosome. The genetic mode of action of Bvr-1 is trans dominant in restriction of murine leukemia virus. The restriction locus results in a block late in virus maturation but prior to release, since expression of antigens for viral structural proteins and matrue budding particles is apparent on surfaces of restriced hybrid cells but not in high-speed pellets from culture fluid of restricted cells.
Bioenergetics in clinical medicine: prevention by forms of coenzyme Q of the inhibition by adriamycin of coenzyme Q10-enzymes in mitochondria of the myocardium.
Authors: Kishi T , Watanabe T , Folkers K
Published: May 2006

Adriamycin inhibits the succinoxidase system and the NADH-oxidase system. Both of the intact mitocondrial enzymes and the pentane-extracted preparations are inhibited. The inhibition can be prevented by a molar ratio of coenzyme to adriamycin of 3:1 for coenzyme Q10 (ubiquinone), 5:1 for coenzyme Q7, and 5:1 for coenzyme Q4. Prevention of inhibition was observed in the decreasing order of coenzyme Q10 greater than coenzyme Q7 greater than H6 coenzyme Q4 greater than coenzyme Q4. Adriamycinone was three times more inhibitory than adriamycin, which is compatible with a less polar fragment necessary to inhibit the lipoidal coenzyme Q10. Daunomycinone was not inhibitory at a concentration at which adriamycinone is effective, indicating that the hydroxyl group of the latter could be binding at the receptor, since it should not influence electron transfer or rings B and C.
Effects of deuterium oxide on mechano-sensory receptor.
Authors: Nakajima S , Kuroda T
Published: May 2006

In the crayfish stretch receptor organ, a total substitution of D2O for H2O in the bathing solution produced a decrease in the amplitude of the receptor potential to a level of 34% of the control. The electrical resistance of the receptor neuron was slightly increased by the D2O substitution. The input capacitance of the neuron was unchanged. The viscoelastic properties of the receptor muscle were not altered by D2O. Thus, we conclude that D2O has an inhibitory effect on the transduction process which links the deformation of the dendrites with the permeability increase that is responsible for the receptor potential.
Delayed singularity formation for solutions of nonlinear partial differential equations in higher dimensions
Authors: John Fritz
Published: May 2006

Strict solutions
u
of genuinely nonlinear homogeneous hyperbolic equations in two independent variables with initial data
f
(
x
) of compact support become singular after a time interval of order ∥
f
∥
-1
. In higher dimensions solutions initially of compact support are likely to have life expectancies of orders ∥
f
∥
-2+ε
at least. This is proved for the special case of solutions
u
(
x
1
,...,

x
n

,
t
) of a second order equation

u
tt

= Σ

i,j

a
ij
u
xixj

, where
n
≥ 3 and where the coefficients

a
ij

are
C
∞
-functions in the first derivatives of
u
, forming a symmetric positive definite matrix.
Chemical reactivities of catalytic and noncatalytic zinc or cobalt atoms of horse liver alcohol dehydrogenase: differentiation by their thermodynamic and kinetic properties.
Authors: Sytkowski A J , Vallee B L
Published: May 2006

Horse liver alcohol dehydrogenase (EC 1.1.1.1) contains one catalytic and one noncatalytic pair of zinc atoms that can be replaced selectively with cobalt and/or 65zince. We have now prepared "hybird" metalloenzymes by specifically replacing one or both pairs of zinc atoms with 65zinc and/or cobalt. Their differential chemical reactivities serve to characterize the metal atoms at either site.The spectral and kinetic properties of the resultant 65zinc, cobalt, and hybrid enzymes, as well as those of their complexes with 1,10-phenanthroline, identify the metal atoms that are at the catalytic sites and differentiate them from those at the noncatalytic sites. All data are in complete agreement with the results of the x-ray crystal structure analysis. Remarkably, under the conditions used, chemical reactivity, as gauged by thermodynamic methods under equilibrium conditions, identifies the catalytic metal atoms as those which are reactive to 1,10-phenanthroline, while this reagnet does not affect the noncatalytic pair. Under dynamic conditions the kinetics of the metal-metal exchange reveals the converse to be true: the chemical reactivity of the noncatalytic atoms is much higher and, hence, they exchange more rapidly. The results are examined in terms of thermodynamic and kinetic properties of metal complex ions which serve as the basis of possible mechanisms underlying these observations.
Maturation of neuroblastoma cells in the presence of dimethylsulfoxide.
Authors: Kimhi Y , Palfrey C , Spector I , Barak Y , Littauer U Z
Published: May 2006

Addition of dimethylsulfoxide at concentrations of 1% and 2% (vol/vol) to cells of mouse neuroblastoma clone NIE-115 in the confluent phase of growth resulted in the production of morphologically differentiated cultures with extensive process formation. Cell maintained in 2% dimethylsulfoxide remained in a stable nondividing condition for periods of up to 4 weeks. A high degree of electrical excitability was found in these cells, but there was no clear correlation of this property with the level of induction of either acetylcholinesterase (acetylcholine hydrolase; EC 3.1.1.7) or tyrosine hydroxylase [L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2]. In addition, intracellular levels of cyclic 3':5'-AMP were not elevated in fully morphologically and electrically differentiated cells. While cell division was markedly inhibited by 2% or higher concentrations of dimethylsulfoxide, at 1% growth continued at a somewhat slowed rate and such cultures exhibited enhanced process formation and electrical activity for a relatively short period. High concentrations (3% or 4%) of dimethylsulfoxide totally suppressed process formation and did not result in increased excitability, but cells maintained high resting potentials. The results suggest that the development of the excitable membrane in neuroblastoma cells may be expressed independently of neurospecific enzyme induction, and does not require a sustained elevation of cyclic 3':5'-AMP levels.
Specific in situ cleavage of 16S ribosomal RNA of Escherichia coli interferes with the function of initiation factor IF-1.
Authors: Baan R A , Duijfjes J J , van Leerdam E , van Knippenberg P H , Bosch L
Published: May 2006

Specific in situ cleavage of 16S rRNA of E. coli has been accomplished by in vitro treatment of 70S ribosomes ("tight couples") with the bacteriocin cloacin DF13. The defective ribosomes, which have fully lost their ability to sustain polypeptide synthesis, are still able to form initiation on complexes with MS2 RNA, but the kinetics are altered. This is apparently due to an improper functioning of initiation factor IF-1, for the defective ribosomal couples respond normally to dissociation by IF-3 but the dissociation is not stimulated by IF-1. The initiation complexes formed with defective ribosomes are fully reactive with puromycin. Their ability to bind alanyl-tRNA is reduced by about 50% at all concentrations of elongation factor Tu studied. Cleavage of the 16S rRNA, not the release of the terminal fragment from the ribosome, causes the block of protein synthesis and the aberrations observed during initiation and elongation.
Control of adenylate cyclase from secretory vesicle membranes by beta-adrenergic agents and nerve growth factor.
Authors: Nikodijevic O , Nikodijevic B , Zinder O , Yu M Y , Guroff G , Pollard H B
Published: May 2006

Adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] activity of purified secretory vesicle membranes from the adrenal medulla is inhibited by I-isoproterenol and I-epinephrine, as well as by nerve growth factor (NGF). The effect of these agents was found to be dose-dependent and, in the case of the catecholamines, saturable. NGF was active at concentrations as low as 10(-8) M. Oxidized NGF was only minimally active, and insulin was completely inactive. Neither dopamine nor phenylephrine had activity. Inhibition of cyclase by either isoproterenol or epinephrine was blocked by I-propranolol, a specific beta-antagonist, but propranolol by itself had no effect on adenylate cyclase activity. The data indicate that the secretory vesicle membrane has beta-adrenergic receptors coupled to the adenylate cyclase. Propranolol was also found to block the NGF-induced inhibition of cyclase. We conclude that the granule membrane has beta-adrenergic receptors as well as NGF-reactive sites, and that the two may be functionally linked.
Effect of concanavalin A on expression of cell surface sialyltransferase activity of mouse thymocytes.
Authors: Painter R G , White A
Published: May 2006

Incubation of mouse thymocytes with mitogenic concentrations of concanavalin A causes a 2-fold increase in cell-surface-associated (but not total cell) sialyltransferase activity (ectosialyltransferase, CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) as judged by incorporation of [14C]sialic acid into endogenous cell acceptors and into added desialylated fetuin acceptor. The concanavalin-A-induced enhancement of enzymic activity is essentially complete within 1 hr after addition of mitogen and remains at elevated levels for 12 hr, declining rapidly thereafter. Intact cells labeled previously with [14C]sialic acid and then incubated briefly with hydrolytic enzymes, including neuraminidase and insoluble trypsin, released 43-66% of total cell-associated radioactivity without appreciably changing cell viability. Alterations in sialyltransferase activity due to concanavalin A treatment could not be explained by a mitogen-mediated (a) uptake of radioactive precursors, (b) cell death, (c) increased product catabolism, or (d) activation of sialyltransferase by mitogen binding to the enzyme. Furthermore, the process does not require active protein synthesis. The results are consistent with a rapid concanavalin-A-induced exposure of potential enzymic activity that was previously inaccessible to substrate.
Cytological evidence for switches in polarity of chromosomal DNA.
Authors: Wolff S , Lindsley D L , Peacock W J
Published: May 2006

From the types of ring chromosomes induced in x-irradiated Chinese hamster ovary (CHO) cells, we deduce the existence of switches in the polarity of chromosomal DNA; if there is a continuous DNA double helix along the full length of the chromosome then the polarity switches imply 3'-3' and 5'-5' phosphodiester linkages. The resolution of the method is such that we estimate that there is one polarity switch for every 10(9) normal 3'-5' phosphodiester bonds.
Ethological isolation and mating experience in Drosophila paulistorum.
Authors: O'Hara E , Pruzan A , Ehrman L
Published: May 2006

With few exceptions, previously published experiments documenting ethological isolation between Drosophila populations have used young virgin females. We have observed directly females of Drosophila paulistorum semispecies in choice experiments with both homogamic and heterogamic males. Aged females' sexual selection did not differ from that of young females. Previous heterogamic copulatory experience did not change the degree of sexual isolation; however, females with homogamic copulatory experience showed a significantly higher preference for homogamic males.
On computing the Discrete Fourier Transform
Authors: Winograd Shmuel
Published: May 2006

New algorithms for computing the Discrete Fourier Transform of
n
points are described. For
n
in the range of a few tens to a few thousands these algorithms use substantially fewer multiplications than the best algorithm previously known, and about the same number of additions.
Ribonuclease H of calf thymus: substrate specificity, activation, inhibition.
Authors: Stavrianopoulos J G , Gambino-Giuffrida A , Chargaff E
Published: May 2006

When the action of highly purified specimens of ribonuclease H (hybrid nuclease; RNA-DNA hybrid ribonucleotidohydrolase; EC 3.1.4.34) of calf thymus on a wide selection of homopolymer hybrids was studied, the extent, and even the occurrence, of hydrolysis was found to be governed by the interplay of several factors: the composition of the ribo strand, the length of the deoxyribo strand, and the nature of the activating metal. Mn2+ activates the enzymic cleavage of all hybrid combinations, Mg2+ only of those containing purine ribo strands, Co2+ only of poly(A) hybrids. A 1:1 hybrid of phage f1 DNA and RNA is, however, split in the presence of any of these activators. Hybrids with deoxyribo tetranucleotides can still be cleaved, but not with dinucleotides. The behavior of hybrids containing covalently linked runs of ribo and deoxyribopolynucleotides was studied with the hybrid poly(dT)-poly(A)7-(dA)X]. This hybrid is attacked by ribonuclease H so that the bulk of the resulting poly(dA) still retains one covalently linked riboadenylic acid end group, whereas a small proportion carries a ribo dinucleotide. Inhibition studies showed that ribonuclease H is inactivated irreversibly by pretreatment with S-adenosylmethionine at 35 degrees, but not at 0 degrees. S-Adenosylhomocysteine also is inhibitory, but not irreversibly; also it is essentially limited to the inhibition of the cleavage of purine ribo strands. When the enzyme is exposed simultaneously to both inhibitors, irreversible inactivation is diminished considerably.
Proton relaxation and charge accumulation during oxygen evolution in photosynthesis
Authors: Wydrzynski T. , Zumbulyadis N. , Schmidt P. G. , Gutowsky H. S. , Govindjee
Published: May 2006

The water proton spin-spin (transverse) relaxation rate of chloroplast suspensions has been measured after each of a series of 2.4 μsec light flashes. The sequence of relaxation rates shows a damped oscillatory pattern with a period of four and peaks after the 3rd, 7th, 11th, and 15th flashes. This result indicates that water proton relaxation can be used to monitor the charge-accumulating states as postulated by Kok and coworkers for the oxygen-evolving mechanism in green plants [(1970)
Photochem. Photobiol.
11, 457-475]. Other experiments [Wydrzynski
et al
. (1975)
Biochim. Biophys. Acta
408, 349-354] have shown that the proton relaxation rate is strongly influenced by membrane-bound manganese in various oxidation states, suggesting that manganese participates in the charge accumulation process during oxygen evolution.
Theoretical studies on pro-leu-gly-nh2 conformation.
Authors: Kang S , Walter R
Published: May 2006

Classical potential function calculations were carried out on the hypothalamic factor Pro-Leu-Gly-NH2. The results indicate that the proposed 10-membered, hydrogen-bonded beta-turn conformation of this tripeptide is a strongly preferred structure. Its stability appears to be inherent in the rather rigid backbone conformation of the leucine residue rather than the hydrogen bond between the carboxamide proton of glycinamide and the C=O of the proline moiety; the glycinamide has little influence on the phi-psi of the leucine backbone structure. The type II beta-turn structure of the Pro-Leu-Gly-NH2 is preferred.
A differentiation stimulating factor induces cell sensitivity to 3':5'-cyclic AMP pulses in dictyostelium discoideum.
Authors: Klein C , Darmon M
Published: May 2006

During the first few hours of starvation, Dictyostelium discoideum amoebae excrete a macromolecule, probably a glycoprotein, which stimulates cell differentiation to aggregation competence. 3':5'-Cyclic AMP pulses, which mimic the chemotactic signal, and this factor (differentiation stimulating factor) are shown to exert a cooperative effect in inducing cell differentiation. Data suggest that the appearance of the factor determines the moment amoebae become responsive to cyclic AMP pulses.
Germ line integration and Mendelian transmission of the exogenous Moloney leukemia virus.
Authors: Jaenisch R
Published: May 2006

Mice were infected with the exogenous Moloney leukemia virus (M-MuLV) at two different stages of development. Either newborn mice (which can be considered as essentially fully differentiated animals) or preimplantation mouse embryos (at the 4-8 cell stage) were infected with M-MuLV. In both cases, animals that had developed an M-MuLV-induced leukemia were obtained. Two lines of evidence indicate that infection of preimplantation embryos, in contrast to infection of newborns, can lead to integration of the virus into the germ line. 1. Viremic males of the first backcross generation (N-1 generation) transmitted the virus to 50% of their offspring (N-2 generation) when mated with uninfected females. Likewise, a 50% transmission was observed from viremic N-2 and N-3 males to the next generations. 2. Molecular hybridization experiments revealed that viremic N-1 and N-2 animals carried one copy of M-MuLV per diploid mouse genome equivalent in all "non-target" organs tested. Together, both experiments indicate that the exogenous M-MuLV can be converted to an endogenous virus after infection of preimplantation embryos. The available evidence suggests that M-MuLV integrated into the germ line at one out of two possible integration sites. Thus, viremic backcross animals are heterozygous for a single Mendelian locus carrying the M-MuLV gene. During leukemogenesis an amplification of the M-MuLV from one copy to a maximum of four copies per diploid mouse genome equivalent takes place in the tumor tissues.