bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastics of cycle completions (fluxes) in biochemical kinetic diagrams.
Authors: Hill T L , Chen Y D
Published: May 2006

Over a long time period, the rate constants for cycle completions (one-way fluxes) in steady-state biochemical diagrams can be expressed explicitly in terms of the elementary rate constants for transitions between states of the diagram. These cycle rate constants determine the mean one-way fluxes in the diagram and also fluctuations about the means. These properties are confirmed by Monte Carlo computer simulations on special cases. Two other topics are considered briefly: the effect of the starting state or states on the numbers of cycle completions in computer simulation runs; and the more detailed stochastic approach required if individual cycle completions are to be followed (i.e., if the "long time" restriction is removed).
Biochemical procedure for production of small deletions in simian virus 40 DNA.
Authors: Carbon J , Shenk T E , Berg P
Published: May 2006

A simple biochemical procedure for producing small deletions (15 to 50 base pairs) at virtually any location in simian virus 40 DNA has been developed. The steps involved are: cleavage of the closed-circular DNA to produce a linear structure followed by 5'-exonuclease digestion to expose a short single-stranded segment at each 3' end of the molecule. Mutants containing deletions at the site of the cleavage are obtained by infecting permissive monkey kidney cells with the exonuclease-treated DNA in the presence or absence of a helper DNA (depending upon whether or not the site of cleavage and therefore the deletion occurred in a gene required for vegetative multiplication). In this paper viable mutants with deletions at the HpaII endonuclease cleavage site (0.735 map position) and defective trans-complementable mutants with deletions at the EcoRI endonuclease cleavage site (0/1.0 map position) were isolated.
Role of epithelial architecture and intracellular metabolism in proline uptake and transtubular reclamation in PRO/re mouse kidney.
Authors: Scriver C R , McInnes R R , Mohyuddin F
Published: May 2006

The homozygous PRO/Re mouse has less than 1 percent of the very high proline oxidase activity that characterizes normal kidney cortex. In PRO/Re mouse the endogenous proline concentration is eight times normal in plasma and four times normal in kidney cortex cell, but 50 times normal in urine. The integrity of the membrane transport systems for proline uptake at the antiluminal surface of absorbing epithelium is retained in PRO/Re kidney, as determined by the slice method. Clearance studies in vivo under steady-state conditions indicate that the integrity of the luminal uptake system shared by glycine and proline, and serving proline absorption, is also intact. The exaggerated renal clearance of proline in PRO/Re mice (50 times normal) is explained when its raised intracellular concentration, caused by impaired proline oxidation, is considered. Backflux into urine flowing down the nephron will occur under these conditions, thus impairing net reclamation of proline in PRO/Re kidney. The findings reveal that membrane transport and intracellular metabolism of a substrate are, indeed, independent functions, but that metabolism of a substance can influence its transcellular transport.
Theory of Homogeneous Dynamos in a Rotating Liquid Sphere
Authors: Pekeris C. L. , Accad Y.
Published: May 2006

A spherical harmonic analysis is made of the hydrodynamic equation governing the flow of an incompressible liquid in a rotating sphere in the presence of the magnetic Lorentz force. Nonlinear partial differential equations are derived for the functions

S
n

(
r,t
) and

T
n

(
r,t
) entering the spherical harmonic representation of the velocity field.
Affinity labeling of the ribosomal decoding site with an AUG-substrate analog.
Authors: Pongs O , Lanka E
Published: May 2006

The trinucleotide AUG was condensed at the 5'-end with N-bromoacetyl-p-aminophenylphosphate. This bromoactylated AUG analog reacted irreversibly with the mRNA binding site of Escherichia coli 70S ribosomes. After reaction of 70S ribosomes with the AUG analog, labeled 30S subunits could be isolated that were programmed for initiation-factor-dependent binding of fMet-tRNAfMet. This shows that this AUG-affinity label reacted in the decoding site for fMet-tRNAfMet. By combination of sodium dodecyl sulfate-, Sarkosyl-, and ureapolyacrylamide gel electrophoresis the AUG-affinity label was found to be irreversibly bound to ribosomal proteins S4, the ram gene product, and S18.
Gross Thermodynamics of Heat Engines in Deep Interior of Earth
Authors: Backus George E.
Published: May 2006

From the gross conservation laws of thermodynamics in a convecting material we derive a bound on the ratio of the rate of production of mechanical or magnetic energy to the rate of internal radioactive heating which drives the convection. Our bound for this “efficiency” depends on the temperatures in the material, and can exceed unity. Whether the bound can be attained by “efficiencies” in real fluids is not known, but a simple machine shows that “efficiencies” larger than unity are physically realizable. Our bound gives upper limits on the viscous dissipation in the earth's mantle and ohmic heating in the core, but these limits are too large to be physically interesting.
T antigen binds to simian virus 40 DNA at the origin of replication.
Authors: Reed S I , Ferguson J , Davis R W , Stark G R
Published: May 2006

A technique employing ferritin-conjugated antibody has been developed to visualize specific protein-DNA complexes in the electron microscope and has been used to demonstrate the preferential binding of simian virus 40 (SV40) T antigen at or near the origin of replication of SV40 DNA, 0.67 fractional length clockwise from the EcoRI restriction endonuclease cleavage site. urified covalently closed supercoiled circles of SV40DNA were treated with partially purified T antigen and the complex was stabilized by crosslinking with glutaraldehyde. Hamster antiT antigen gamma-globulin, ferritin-labeled goat anti-hamster gamma-globulin, and glutaraldehyde were then added sequentially. The location of the bound ferritin cores was measured with respect to the EcoRI cleavage site and the orientation of the cores relative to the ends of the DNA was determined with respect to the locations of Escherichia coli DNA unwinding protein, which binds to covalently closed supercoiled SV40 DNA at either of two preferred sites, 0.46 or 0.90 fractional length clockwide from the EcoRI cleavage site.
Nonspecific nature of the stimulus to DNA synthesis in cultures of chick embryo cells.
Authors: Rubin H
Published: May 2006

The rate of DNA synthesis in chick embryo cultures deprived of serum is stimulated 5- to 20-fold by a large variety of substances, including subtoxic concentrations of certain metal ions such as Zn++, Cd++, and Hg++. The stimulatory concentrations of Zn++ and Cd++ have sharp optima, which are just below the concentrations that produce frank morphological damage in each case. A much wider gap exists between stimulatory and morphologically damaging concentrations of Hg++. These metal ions also stimulate RNA synthesis, and the uptake of 2-deoxy-D-glucose. The stimulatory effects of Zn++, but not those of Hg++, are prevented by treatment with EDTA. Although medium from cultures stimulated by Zn++ or Hg++ retains its stimulatory capacity for a new set of cultures, the capacity in the case of Zn++-treated cultures is almost entirely lost upon addition of EDTA. It is also lost upon dialysis of conditioned medium from cultures treated with either Zn++ or Hg++. It is concluded that the stimulatory effect is the direct result of interaction between metal ions and cells, and not to the release of growth-stimulatory materials from the cells. The stimulation is thus seen as a non-specific event resulting in an integrated, metabolic response by the cells.
South American mammal zoogeography: evidence from convergent evolution in desert rodents.
Authors: Mares M A
Published: May 2006

Current theories regarding colonization of South America by mammals are divided between those supported by fossil evidence, which suggest the original mammal fauna of the isolated continent was augmented by early immigrants (primates, caviomorph rodents, and later, procyonids) with a final large influx of northern mammals occurring with the formation of the Panama land bridge, and an opposing view which states that the purported "recent invaders" are too taxonomically and ecologically differentiated to have colonized since the land bridge arose. The second theory suggests that most extant mammals entered before the Plio-Pleistocene land connection. An analysis of degree of physiological adaptation, natural history, distribution patterns, and a multivariate assessment of convergent evolution of Monte Desert rodents indicate that South American cricetine rodents are not highly specialized for desert life. Their degree of adaptation could be accounted for, in large part, by adaptations for arid or semiarid Andean habitats. No Monte Desert rodent has developed the specialized desert traits that have evolved in most desert rodent faunas of the world, although extinct marsupials similar to living bipedal desert rodents were present in the Monte as recently as late Pliocene. Evidence suggests that Monte caviomorphs have been associated with the desert for a longer period than cricetines, and that the latter represent a fairly recent invasion of the Monte Desert. The data thus support the first hypothesis of South American mammal colonization.
Fall-Off from Extrapolated Values of All Chemical Reactions at Very High Temperatures
Authors: Eyring Henry , Leu An-Lu
Published: May 2006

At high temperatures the breaking of chemical bonds becomes relatively easy and the slow step in a chemical reaction shifts to the rate at which energy can seep into the bond that is to break. This has been observed by various investigators. A new general theory of reactions is developed here to explain this limiting rate at high temperatures. In the case of cyclopropane and cyclobutane the theory leads to the conclusion that 20 degrees of freedom form a heat reservoir which feeds the energy into the carbon bond that is to break and that this rate becomes controlling above about 1200°K. This would correspond to 20 of the 21 vibrational bonds of cyclopropane feeding energy into the carbon bond that is to break, and there would be no noticeable rise in the number of bonds for cyclobutane. This theory is especially important for shock tubes and detonations, where this falling-off from the extrapolated low temperature rate becomes glaringly obvious.
Inhibition by interferon of delayed-type hypersensitivity in the mouse.
Authors: De Maeyer E , De Maeyer-Guignard J , Vandeputte M
Published: May 2006

The effect of interferon on delayed-type by persensitivity to picryl chloride and sheep erythrocytes was examined in the mouse. When administered to sensitized animals on the day before or the day of challenge, tissue culture interferon inhibited both the ear swelling induced by pieryl chloride and footpad swelling induced by sheep erythrocytes. Newcastle disease virus, when injected into sensitized If-1l or If-1h congenic mice a few hours before challenge, caused an inhibition of delayed-type hypersensitivity which could be related to the amount of serum interferon induced by the virus. These results indicate that interferon production may represent one of the factors responsible for the depression of cell-mediated immune reactions during virus infection.
Separation of two responses to auxin by means of cytokinin inhibition.
Authors: Vanderhoef L N , Stahl C A
Published: May 2006

A continuous growth apparatus was used to measure the effect of cytokinin on auxin-induced elongation. The soybean hypocotyl segments elicited a bi-phasic response to auxin that appeared to be two overlapping responses. The first response, which began 12 min after auxin addition, was not inhibited by cytokinin, even after long preincubation in cytokinin, but the second response to auxin, which began about 30 min after auxin addition, was completely inhibited by cytokinin. Such overlapping reactions are shown, depending on the amount of overlap, to yield a variety of summation reactions, many of which resemble rate-time curves that have been previously reported. We have shown that the transient first phase of auxin-induced elongation is very similar to acid-activated growth, while the second phase is long lasting and very likely identical to the long-term response to auxin, as extensively studied in Avena, soybean, and other elongating cells.
Subversion of immune system by tumor cells and role of prostaglandins.
Authors: Plescia O J , Smith A H , Grinwich K
Published: May 2006

Mice bearing syngeneic tumors, chemical and virus-induced, became immunologically unresponsive to sheep erythrocytes. The increase in the degree of unresponsiveness with tumor growth suggested a causal relationship. Immunosuppression was in fact caused by the tumor cells because the addition of tumor cells to in vitro cultures of spleen cells and sheep erythrocytes resulted in suppression of antibody response. Suppression was dose dependent with a ratio of 1 to 1000 of tumor cells to spleen cells sufficient to produce significant suppression. Prostaglandins were found to have a role in immunosuppression by tumor cells in that PGE2 was itself immunosuppressive and in that indomethacin and aspirin, inhibitors of prostaglandin synthetases, blocked immunosuppression in vitro and retarded tumor growth in vivo. These findings suggest that tumors, although antigenic, may be able to escape immuno-sureillance by their host by means of subverting the immune system. Thus, success of immunotherapy may well depend on our ability to prevent or block the immunosuppressive activity of tumors.
Biochemically differentiated mouse glial lines carrying a nervous system specific cell surface antigen (NS-1).
Authors: Sundarraj N , Schachner M , Pfeiffer S E
Published: May 2006

Six biochemically differentiated clonal lines have been established from a transplantable glioma (tg26) of the C57BL/6 inbred mouse strain. Antibodies have been previously raised against G26 tumor cells, which define a cell surface component(s), NS-1 (nervous system antigen-1), found exclusively in the nervous system. NS-1 concentrations approximate the levels of the original G26 tumor when the clonal lines are grown as clonal tumors in vivo, but are reduced when the cells are grown in vitro. NS-1 concentrations are further reduced in vitro upon incubation of the cells with 1 mM dibutyryl 3:5-cyclic AMP. H-2 histocompatibility antigen concentration, in contrast, is unaffected by dibutyryl cAMP. In addition to expressing NS-1, the neuroectodermal origin of these cell lines is further confirmed by their synthesis of the nervous system specific acidic protein S-100 and by the high specific activity of the enzyme 2:3-cyclic nucleotide 3-phosphohydrolase. In addition, they respond to catecholamines by the elevation of intracellular 3:5-cyclic AMP levels. Whereas expression of S-100 protein is high under in vitro conditions but negligible after one passage in vivo, 2:3-cyclic nucleotide 3-phosphohydrolase is not detectable in vitro but becomes detectable again in vivo. The two membrane-bound constituents, NS-1 and 2:3-cyclic nucleotide 3-phosphohydrolase, therefore seem to be subjected to different regulatory mechanisms from that of the soluble, intracellular S-100 protein.
Presence of two polypeptide chains comprising fatty acid synthetase.
Authors: Stoops J K , Arslanian M J , Oh Y H , Aune K C , Vanaman T C , Wakil S J
Published: May 2006

Highly purified fatty acid synthetases of chicken and rat livers have molecular weights of 500,000 and dissociate in solutions of low ionic strength into subunits of molecular weight 250,000 with loss of synthetase activity. The subunits can be reassociated in phosphate buffer with full restoration of the activity. In the presence of sodium dodecyl sulfate or guanifine-HCl, the synthetases dissociate into polypeptide chains of molecular weight 220,000 as determined by sodium dodecyl sulfate-gel electrophoresis and sedimentation equilibrium. The polypeptide contains the 4-phosphopantetheine group and the [14C]acetyl and [4C]malonyl groups if the synthetases were prelabeled with [14C]acetyl-CoA and [14C]malonyl-CoA. Similar results were obtained with the synthetase from yeast, except the subunit has a molecular weight of 200,000. These observations indicate that the multi-catalytic activities of the synthetases and the acyl carrier protein are associated only with the two polypeptide chains. The findings suggest a novel structural organization for multienzyme complexes.
Utilization of L-cystine by the gamma-glutamyl transpeptidase-gamma-glutamyl cyclotransferase pathway.
Authors: Thompson G A , Meister A
Published: May 2006

Cystine is a good acceptor of the gamma-glutamyl group of gamma-glutamyl donors in the reaction catalyzed by gamma-glutamyl transpeptidase. The product of the enzymatic reaction and an authentic sample of gamma-glutamylcystine were shown to exhibit identical chromatographic and electrophoretic behaviors; acid hydrolysis gave equimolar amounts of cystine and glutamate. In studies with two gamma-glutamyl donors, apparent Km values in the neighborhood of 0.3 mM were found for L-cystine; these values are not far from the concentrations of L-cystine in mammalian blood plasma. At an amino-acid acceptor concentration of about 0.5 mM, L-cystine is somewhat more active than L-glutamine, and much more active than L-cystein. L-gamma-Glutamyl-L-cystine was found to be a good substrate of gamma-glutamyl cyclotransferase. These observations thus indicate that L-cystine is a very active substrate of the gamma-glutamyl transpeptidase-gamma-glutamyl cyclotransferase pathway. In relation to the hypothesis that the gamma-glutamyl cycle functions in animo-acid transport, it may be significant that glutathione (which is the most abundant intracellular form) is a much better gamma-glutamyl donor than glutathione disulfide, while the predominant extracellular form-cystine-is a much better gamma-glutamyl acceptor substrate than cystein.
Brdicka currents observed with bovine serum albumin and completely reduced bovine serum albumin in the presence of urea.
Authors: Kolthoff I M , Yamashita K , Hie T B
Published: May 2006

In ammonia buffers of varying composition and pH, native bovine serum albumin and completely reduced bovine serum albumin, denoted by p(SH)35, yield quite different Brdicka current-voltage (i-E) curves, but they are identical in the presence of 5 mM calcium chloride. This means that in the presence of calcium, bovine serum albumin becomes completely reduced to p(SH)35. In 8 M urea and ammonia buffers the Brdicka i-E patterns of serum albumin and p(SH)35 are identical even in the absence of calcium, the effect of calcium on the first wave being negligible while calcium slightly increases the second wave. The maximum polarographic effect is attained at urea concentrations of about 5-6 M. Quite generally, the appearance of a second Brdicka wave is attributed to complexation of Co(II) with S- and a group of ligands that is different on the second than on the first wave. The effect of calcium on Brdicka currents of bovine serum albumin in the absence of urea is attributed to an orientation of the protein on the surface of the electrode such that all disulfide groups are reduced and with other ligands can complex with Co(ii). Denaturation of bovine serum albumin in buffers with a pH less than 10.5, and which are 8 M in area, is (polarographically) completely reversible if dilution is made within 15 minutes after preparation. Changes in Brdlcka I-E patterns upon longer aging at varying pH are attributed-in part at least-to dimerization of the denatured protein by interaction of pS- in one molecule with -S-S-in another.
Lymphokine-induced production and release of lysosomal enzymes by macrophages.
Authors: Pantalone R M , Page R C
Published: May 2006

MACROPHAGES ARE ASSOCIATED WITH MOST CHRONIC INFLAMMATORY LESIONS, AND THESE CELLS CONTAIN ENZYMES THAT ARE ABLE TO DESTROY CONNECTIVE TISSUE CONSTITUENTS. Normal lymphoid cells responding to a mitogen, phytohemagglutinin-P, release factor(s) that cause a marked increase in the size and enzyme content for mononuclear phagocytes maintained in culture. The stimulated macrophages, which by several criteria remain otherwise viable and healthy, selectively release large quantities of hydrolytic enzymes to the culture medium.
Natural selection and the evolution of reproductive effort.
Authors: Hirshfield M F , Tinkle D W
Published: May 2006

Reproductive effort is defined as that proportion of the total energy budget of an organism that is devoted to reproductive processes. Reproductive effort at a given age within a species will be selected to maximize reproductive value at that age. Reproductive effort is not directly affected by changes in juvenile survivorship, nor necessarily reduced by an increase in adult survivorship. Selection for high levels of reproductive effort should occur when extrinsic adult mortality is high, in environments with constant juvenile survivorship, and in good years for juvenile survivorship in a variable environment, provided that the quality of the year is predictable by adults. Data necessary to measure reproductive effort and to understand how selection results in different levels of effort between individuals and species are discussed. We make several predictions about the effect of increased resource availability on reproductive effort. The empirical bases for testing these predictions are presently inadequate, and we consider data on energy budgets of organisms in nature to be essential for such test. We also conclude that variance in life table parameters must be known in detail to understand the selective bases of levels of reproductive effort.
Picosecond detection of an intermediate in the photochemical reaction of bacterial photosynthesis.
Authors: Rockley M G , Windsor M W , Cogdell R J , Parson W W
Published: May 2006

Preparations of photosynthetic reaction centers from Rhodopseudomonas sphaeroides were excited with flashes lasting approximately 8 psec. Immediately after the excitation, there appeared a transient state which was characterized by new absorption bands near 500 and 680 nm, by a bleaching of bands near 540, 600, 760, and 870 nm, and by a blue shift of a band near 800 nm. The transient state decayed with an exponential decay time,t, of 246 plus or minus 16 psec after the flash. As the transient state decayed, the radical cation of the reaction center bacteriochlorophyll complex appeared. This indicates that the transient state is an intermediate in the photooxidation of the bacteriochlorophyll. The absorpiton spectrum of the transient state shows the state to be identical with a state (P-F) which has been detected previously in reaction centers that are prevented from completing the photooxidation, because of chemical reduction of the electron acceptor. Analysis of the spectrum suggests that the formation of P-F involves electron transfer from one bacteriochlorophyll molecule to another within the reaction center, or possibly from bacteriochlorophyll to the bacteriopheophytin of the complex. The initial absorbance changes after flash excitation also include a bleaching of an absorption band at 800 nm. The bleaching decays with tau approximately equal to 30 pse. The bleaching appers not to be a secondary effect, but rather to revael another early step in the primary photochemical reaction.
NAD-dependent inhibition of protein synthesis by Pseudomonas aeruginosa toxin,.
Authors: Iglewski B H , Kabat D
Published: May 2006

Pseudomonas aeruginosa toxin (PA toxin) inhibits protein synthesis in a reticulocyte cell-free system. The inhibition requires NAD and results in a block at an elongation step of polypeptide assembly. PA toxin was found to act like diphtheria toxin fragment A. Both toxins catalyze the transfer of radioactivity from nicotinamide(U-14-C)adenine dinucleotide ((14-C)NAD) into covalent linkage with the 100,000 dalton elongation (EF-2) protein. Furthermore, in the presence of a limiting amount of EF-2, excess toxin, and (14-C)NAD, the two toxins were non-additive in the amount of label transferred to EF-3. Unlike free fragment A of diphtheria toxin, the enzymatic activity of PA toxin is heat labile and neutralizable with antibody to PA toxin but not with antibody to fragment A. Although PA and diphtheria toxins have different cellular specificities and molecular properties and produce different clinical symptoms, their intracellular mechanisms of action appear to be identical.
Adenosine 3':5'-cyclic monophosphate as mediator of catabolite repression in Escherichia coli.
Authors: Epstein W , Rothman-Denes L B , Hesse J
Published: May 2006

Measurements of intracellular adenosine 3':5'-cyclic monophosphate (cAMP) concentrations in E. coli under a variety of conditions show that levels of this nucleotide are well correlated with the rate of synthesis of beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) in both catabolite repression and transient repression. These results, combined with extensive genetic and in vitro studies from a number of laboratories on the role of cAMP in E. coli, provide strong support for the concept that intracellular cAMP levels mediate the effects of catabolite and transient repression on rates on enzyme synthesis. Under all conditions studied, excretion can be described by a single rate constant, 2.1 min-1 at 37 degrees, indicating that intracellular levels cannot be regulated by alterations in the rate of cAMP excretion. Our data are fully consistent with the idea that carbon sources control intracellular cAMP levels by effects on its synthesis.
Model for regulation of Escherichia coli DNA repair functions.
Authors: Gudas L J , Pardee A B
Published: May 2006

A feedback loop for the regulation of the rec/lex-mediated DNA repair system is proposed. This model was formulated from experiments on the genetic and metabolic regulation of the rate of synthesis of protein X performed in this laboratory, and from genetic data obtained in other laboratories. Protein X is proposed to prevent DNA degradation by the recBC-coded exonuclease. The model states tht: (1) The lex (or exrA in E. coli B) gene codes for a repressor. (2) This repressor binds to an operator region of DNA consisting of the tif-zab region at 51 minutes on the E. coli chromosome. (3) The operator region controls the production of several proteins involved in DNA repair, including protein X. (4) The recA gene product is required to remove the lex-coded repressor from the operator. Thre recA gene could code for an antirepressor (inducer protein or a protease) or a modifer of recBC nuclease action; (5) Low molecular weight products of DNA degradation are effectors that activate the system. (6) Protein X limits recBC nuclease action by binding to single-stranded DNA.
Temperature-sensitive RNA polymerase mutants with altered subunit synthesis and degradation.
Authors: Kirschbaum J B , Claeys I V , Nasi S , Molholt B , Miller J H
Published: May 2006

A temperature-sensitive mutant having a lethal mutation in the gene for the beta subunit of RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) exhibits an apparent 2- to 3-fold decrease in the rates of both beta and beta' subunit synthesis at the non-permissive temperature, relative to total protein. In contrast, a temperature-sensitive mutant with a lethal mutation in the gene encoding beta' has a 5- to 6-fold increase in the rates of beta and beta' synthesis at 42 degrees. These beta and beta' mutants also exhibit rapid degradation of both subunits at the high temperature.
An Algebraic Description of Stereochemical Correspondence
Authors: Nourse James G.
Published: May 2006

It is shown that a stereochemical correspondence between two molecular systems can be represented by a commuting diagram of the point groups and permutation groups involved. The effect of the diagrammatic condition on the mappings of the cosets, double cosets, subgroup lattice, and double coset algebra determined for the two molecular systems by point group to permutation group homomorphisms is detailed. Chemical similarities implied by a stereochemical correspondence are indicated, and six examples are provided and discussed.
Viral and cellular DNA synthesis in nuclei from human lymphocytes transformed by Epstein-Barr virus.
Authors: Benz W C , Strominger J L
Published: May 2006

A DNA-synthesizing system in vitro, using nuclei prepared by treatment of human lymphocytes with the detergent Brij 58, was developed. Nuclei from cultured lymphocytes synthesized DNA for as long as 5 hr, and required ATP, deoxynucleoside triphosphates, magnesium, and a calcium chelator. In nuclei from a partially synchronized line of cultured lymphocytes carrying several hundred copies of the Epstein-Barr viral genome, synthesis in vitro was predominately viral in early S phase and cellular in late S phase. These and other data suggested that the DNA synthesis observed in vitro was predominately replicative.
3'-Terminal nucletide sequence (n equals 361) of bacteriophage MS2 RNA.
Authors: Vandenberghe A , Min Jou W , Fiers W
Published: May 2006

32P-Labeled MS2 RNA was partially digested with ribonuclease T1 (guanyloribonuclease; ribonucleate 3'-guanylo-oligonucleotidohydrolase; EC 3.1.4.8) or with epilson-carboxymethyl-lysine-41 pancreatic ribonuclease A (ribonucleate 3'-pyrimidino-oligonucleotidohydrolase; EC 3.1.4.22). A series of overlapping fragments was obtained which allowed the reconstruction of a 361-nucleotide-long 3'-terminal sequence. A unique reading frame could be deduced, which indicated that the replicase gene ends with a U-A-G termination signal and is followed by a 174-nucleotide-long untranslated segment.
Homology and relationship between the genomes of papovaviruses, BK virus and simian virus 40.
Authors: Khoury G , Howley P M , Garon C , Mullarkey M F , Takemoto K K , Martin M A
Published: May 2006

A number of hybridization techniques have been used to assess the homology between the genomes of BK virus (BKV) and simian virus 40 (SV40). A noncontiguous set of homologous sequences has been localized primarily within the late region of the SV40 genome, and these sequences presumably account for the cross-reaction between V-antigens of the two viruses. The reason for the relatively strong crossreaction between SV40 and BKV T-antigens is still unclear. The sequence homology and similarity in genomic organization suggest a close relationship between these papovaviruses.
Oxygen exchange in the gamma-phosphoryl group of protein-bound ATP during Mg2+-dependent adenosine triphosphatase activity of myosin.
Authors: Bagshaw C R , Trentham D R , Wolcott R G , Boyer P D
Published: May 2006

When ATP binds to myosin in the presence of Mg2+ there follows a rapid cleavage reaction to yield a myosin-product complex whose breakdown is rate-limiting in the overall adenosine triphosphatase reaction at 21 degrees and pH 8.0. Recent kinetic studies on this system have led to the proposal that the cleavage of ATP bound to myosin is reversible. This conclusion is based in part on the observation that when ATP is mixed with an excess of myosin active sites a small amount of tightly bound ATP exists whose life-time coincides with that of the myosin-product complex and implies these two species are in equilibrium during their decay. Previous oxygen exchange studies have shown that phosphate released as free product contains more than one oxygen atom from water. A rapid equilibration between myosin-bound ATP and a myosin-products complex can account for the extra water oxygen incorporation of the product phosphate. Such a model requires that the gamma-phosphoryl group of the bound ATP also exchanges its oxygen atoms with water. Results presented in this paper show that protein-bound ATP labeled in the three terminal oxygen atoms of the gamma-phosphoryl group with 18O exchanges about 75% of its label within 2 s of binding to the active site of myosin. This result provides chemical evidence for a model in which bound ATP undergoes a reversible reaction with water. Incomplete exchange may arise from kinetic and/or structural restraints on the mechanism and plausible models are discussed.
Apparent dependence of interactions between cytochrome b5 and cytochrome b5 reductase upon translational diffusion in dimyristoyl lecithin liposomes.
Authors: Strittmatter P , Rogers M J
Published: May 2006

Dimyristoyl lecithin liposomes, containing cytochrome b5 reductase (NADH:ferricytochrome b5 oxidoreductase, EC 1.6.2.2) and varying amounts of cytochrome b5, were used to measure flavoprotein catalysis alone and catalysis requiring electron transfer between the reductase and cytochrome as a function of temperature. Whereas flavoprotein catalysis showed a simple linear temperature dependence in an Arrhenius plot, the reaction involving electron transfer between the two bound enzymes showed a marked, 4-fold, change in rate at the crystalline-liquid crystalline phase transition of the hydrocarbon chains of the lecithin vesicles and a second, minor change involving the minor transition. These data represent strong evidence that protein-protein interactions in this membrane model system are dependent upon translational diffusion of nonpolar segments of the proteins in the hydrocarbon region of the phospholipid bilayer.
Appearance of smaller mannosyl-glycopeptides on the surface of a human cell transformed by simian virus 40.
Authors: Ceccarini C
Published: May 2006

When fucosyl surface glycopeptides from growing normal human cells (WI 38) were compared with those derived from nongrowing cells the former were enriched in high-molecular-weight species. However, a line of human cells (WI 18Va) transformed by simian virus 40 appeared to have fucosyl-glycopeptides similar in size distribution to those from rapidly growing non-transformed cells (WI 38). I propose that the enrichment in high molecular weight species in these cells might be growth- rather than transformation-dependent. Using radioactive mannose to label surface glycopeptides, I observed that those derived from transformed cells (WI 18Va) were smaller than those from rapidly growing normal cells. Thus differences in size distribution may not be adequate criteria to evaluate the growth-dependent alterations in cell surface glycopeptides.
Protein kinase and its regulatory effect on reverse transcriptase activity of Rous sarcoma virus.
Authors: Lee S G , Miceli M V , Jungmann R A , Hung P P
Published: May 2006

We have studied the effect of protein phosphokinase (EC 2.7.1.37; ATP:protein phosphotransferase) and phosphoprotein phosphatase (EC 3.1.3.16; phosphoprotein phosphohydrolase) on reverse transcriptase (RNA-dependent DNA nucleotidyltransferase) activity of Rous sarcoma virus. Protein kinase from Rous sarcoma virus-transformed chick embryo fibroblasts was purified by DEAE-cellulose chromatography, Sephadex gel filtration, and isoelectric focusing. Purified reverse transcriptase from Rouse sarcoma virus was preincubated with protein kinase and ATP under conditions allowing incorporation of phosphate into substrate protein. After the preincubation, reverse transcriptase activity was assayed in the presence of poly(rA).oligo(dT) as template. A 2- to 5-fold increase of reverse transcriptase activity was found after the preincubation of reverse transcriptase with protein kinase and ATP. Incubation of reverse transcriptase with heat-treated, inactive protein kinase and ATP had no effect on transcriptase activity. When the transcriptase preparation was incubated with protein kinase and [gamma-32P]ATP and subsequently purified by chromatography on phosphocellulose and Sephadex gel filtration, significant amounts of 32P-labeled proteins were found in the fractions exhibiting reverse transcriptase activity, suggesting 32P incorporation into transcriptase or transcriptase-associated proteins. A 20-60% decrease of reverse transcriptase activity was observed after incubation of reverse transcriptase with phosphatase. The results suggest that phosphorylative modification of reverse transcriptase may be critical in the regulation of reverse transcriptase-catalyzed DNA synthesis.
Sigma cycle during in vitro transcription: demonstration by nanosecond fluorescence depolarization spectroscopy.
Authors: Wu C W , Yarbrough L R , Hillel Z , Wu F Y
Published: May 2006

Studies of RNA chain initiation have suggested that the sigma subunit of Escherichia coli RNA polymerase (RNA nucleotidyltransferase; nucleosidetriphosphate: RNA nucleotidyltransferase; EC 2.7.7.6) is released from the enzyme-template complex during transcription and may be reused by another core polymerase. Nanosecond fluorescence depolarization spectroscopy was used to follow the sigma cycle. Isolated sigma subunit labeled with the fluorescent probe dansyl (DNS) chloride bound stoichiometrically to core polymerase and stimulated transcription of phage T7 DNA to the same extent as did unlabeled sigma. DNS-sigma showed an exponential fluorescence anisotropy decay corresponding to a rotational correlation time of about 100 nsec. This value was unaffected by addition of T7 DNA, but increased about 6-fold when core polymerase was added, and increased further when T7 DNA was added. Such increases are expected for the formation of molecular complexes. Using the anisotropy decays for free DNS-sigma and DNS-sigma-core enzyme bound to T7 DNA, we calculated theoretical decay curves for various mixtures of free and bound sigma. Comparison of the observed anisotropy decay with the calculated curves indicated that about 55% of DNA-sigma was released from the enzyme-T7 DNA complex in the presence of four nucleoside triphosphates under low salt conditions. Sigma release did not occur if rifampicin was added prior to addition of four nucleoside triphosphates or if only three nucleoside triphosphates were present. After sigma was released, addition of core polymerase with rifampicin reduced the free sigma to less than 15%, indicating that the released sigma was accessible to the added core enzyme. Thus these studies have provided physical evidence for the sigma cycle during in vitro transcription.
Electron microscope study of native and crosslinked rabbit muscle phosphofructokinase.
Authors: Telford J N , Lad P M , Hammes G G
Published: May 2006

Electron microscopy of native and dimethyl-suberimidate crosslinked rabbit muscle phosphofructokinase (EC 2.7.1.11; ATP:D-fructose-6-phosphate 1-phosphotransferase) has been carried out using negative staining with sodium phosphotungstate. The results obtained suggest the protomer of molecular weight 80,000 can be approximated as a prolate ellipsoid with axes of 67 A and 25 A. The dimer, which is the fundamental unit for polymerization, is formed by association along the 25 A axis and has approximately dimensions of 67 A X 55 A X 25 A. The tetramer appears to be formed by an end-to-end aggregation of dimers, and the octamer is a sheet-like structure made up of a side-to-side aggregation of tetramers. Higher crosslinked aggregates and long crosslinked filaments also are seen. The filaments have a constant width of about 250 A, are about 0.5 mum in length, and appear to involve tetramers as a fundamental structural unit. The functional significance of the filament structure is not known.
Human synoviocytes: activation and desensitization by prostaglandins and 1-epinephrine.
Authors: Newcombe D S , Ciosek C P , Ishikawa Y , Fahey J V
Published: May 2006

The human synoviocyte increases its intracellular adenosine 3':5'-cyclic monophosphate (cAMP) concentration significantly after incubation with prostaglandin E1, prostaglandin E2, or l-epinephrine. The cells can be desensitized to these same hormones. Hormone-induced desensitization is receptor site specific and associated with a significant increase in intracellular 3':5'-cyclic AMP phosphodiesterase (EC 3.1.4. 17; 3':5'-cyclic AMP 5'-nucleotidohydrolase) activity, whereas cAMP-induced desensitization is not hormone specific.
Chromatin and DNA synthesis associated with nuclear membrane in germinating cotton.
Authors: Clay W F , Katterman F R , Bartels P G
Published: May 2006

The synthesis of nuclear DNA and possible attachment sites of chromatin in the cells of cotton (Gossypium barbadense) radicles during germination was investigated. Biochemical analysis of nuclear membrane fragments or Sarkosyl-magnesium-membrane complexes indicates that the DNA, including newly replicated DNA, is attached to the nuclear membranes during periods of active synthesis. Electron micrographs of nuclear membrane fragments indicate a physical association between chromatin fibers and the membranes. The attachment site appears to be proteinaceous, since the chromatin is released by protein degradative enzymes as evidenced by biochemical techniques and electron microscopic observations. Short-term labeling results in incorporation into a membrane-associated product indistinguishable from the bulk of nuclear DNA. DNA polymerase activity is also associated with nuclear membrane preparations in which [3H]thymidine triphosphate is incorporated into an acid-insoluble. DNase-sensitive product.
Chemotactic signals induce cell differentiation in Dictyostelium discoideum.
Authors: Darmon M , Brachet P , Da Silva L H
Published: May 2006

Experiments carried out with the aid of cellophane membranes demonstrate that the morphogenetic block of certain nonaggregating, "aggregateless," mutants may be overcome by diffusible factors excreted by aggregating wild-type cells. The same differentiation process into aggregation-competent cell is observed if mutant amoebae are subjected to external 3':5'-cAMP pulses imposed at 5 min intervals. Wild-type amoebae also respond to cAMP pulses, since the onset of differentiation is more precocious in pulsed than in unpulsed populations. These data suggest that chemotactic signals act as an inducer of cell differentiation.
Enhanced representation of HL-A antigens on human lymphocytes after mitogenesis induced by phytohemagglutinin or Epstein-Barr virus.
Authors: McCune J M , Humphreys R E , Yocum R R , Strominger J L
Published: May 2006

The amount of HL-A antigens present on the peripheral blood lymphocytes of a single human donor was increased about 11-fold after stimulation with phytohemagglutinin and 36-fold after transformation with Epstein-Barr virus. This increase applied to all four HL-A specificities of these cells. The response to phytohemagglutinin was dependent on dose and was first observed at 12 hr of incubation. Measurements of the amount of surface membranes by geometry, by radioiodinatable surface proteins, and by 5'-nucleotidase (5'-ribonucleotide phosphohydrolase, EC 3.1.3.5) assay all indicated that the enhanced representation of HL-A antigens after stimulation by phytohemagglutinin or transformation by Epstein-Barr virus must be due to an increase in the density of these antigens on the cell surface.
Transient response to chemotactic stimuli in Escherichia coli.
Authors: Berg H C , Tedesco P M
Published: May 2006

We have followed by eye and with the tracking microscope the rotational behavior of E. coli tethered to coverslips by their flagella. The cells change their directions of rotation at random, on the average about once a second. When an attractant is added or a repellent is subtracted, they spin clockwise (as viewed through the coverslip, i.e., along the flagellum toward the body) for many seconds, then counter-clockwise for many seconds, and then gradually resume their normal mode of behavior. The time interval between the onset of the stimulus and the clockwise to counter-clockwise transitiion is a linear function of the change in receptor occupancy. The cells adapt slowly at a constant rate to the addition of an attractant or the subtraction of a repellent. They adapt rapidly to the subtraction of an attractant or the addition of a repellent. Responses to mixed stimuli can be analyzed in terms of one equivalent stimulus.
The triplet state in bacterial photosynthesis: Possible mechanisms of the primary photo-act
Authors: Thurnauer Marion C. , Katz Joseph J. , Norris James R.
Published: May 2006

In vitro
and
in vivo
triplet state electron paramagnetic resonance (epr) spectra of bacteriochlorophylls (Bchls) show important differences in (
a
) electron spin polarization (esp), and (
b
) zero field splitting (ZFS) parameters. The unusual esp and ZFS properties of the observed
in vivo
triplet state are best interpreted as arising from a short-lived radical pair precursor (not directly observable by epr) formed in or with the special pair of bacteriochlorophyll molecules involved in the primary photo-act.
Synthesis and biological properties of a 9,11-azo-prostanoid: highly active biochemical mimic of prostaglandin endoperoxides.
Authors: Corey E J , Nicolaou K C , Machida Y , Malmsten C L , Samuelsson B
Published: May 2006

The 9,11-azo-prostanoid III [(5Z, 9alpha, 11alpha, 13E, 15S)-9, 11-azo-15-hydroxyprosta-5,13-dienoic acid] has been obtained by synthesis and tested for biological activity in systems which are responsive to the prostaglandin endoperoxides PGH2 (I) and PGG2 (II). The azo analog III is a powerful mimic of these endoperoxides with reference to platelet aggregation and release of serotonin when added to human platelet-rich plasma. The analog III is substantially more active (about 7 fold) than PGG2 in stimulating muscle contraction in the isolated rabbit aorta strip. The very great stability of III relative to PGH2 and PGG2 and its potency as a mimic of these important substances suggest that this azo analog will be of considerable value in future studies of the prostaglandin endoperoxides.
Activation of bovine factor X (Stuart factor): conversion of factor Xaalpha to factor Xabeta.
Authors: Fujikawa K , Titani K , Davie E W
Published: May 2006

Bovine factor X (molecular weight 55,100) is a blood coagulation factor present in plasma in a precursor or zymogen form. It is a glycoprotein which has been isolated as a two-chain structure held together by one or more disulfide bonds. During the coagulation process, factor X is converted to a serine protease by the hydrolysis of a specific peptide bond in the amino-terminal region of the heavy chain. This cleavage occurs between Arg-51 and Ile-52, giving rise to factor Xaalpha (molecular weight 45,300) and an activation peptide (molecular weight 9500). Factor Xaalpha is then converted to factor Xabeta (molecular weight 42,600) by hydrolysis of a second specific peptide bond in the carboxyl-terminal region of the heavy chain. This cleavage occurs between Arg-290 and Gly-291, giving rise to a second glycopeptide (molecular weight 2700). Factor Xaalpha and factor Xabeta have equivalent coagulant activity, indicating that the cleavage of the second peptide bond is unrelated to the activation process.
Intramolecular crosslinking of tropomyosin via disulfide bond formation: evidence for chain register.
Authors: Lehrer S S
Published: May 2006

Rabbit skeletal muscle tropomyosin can be crosslinked in the native state by the use of 5,5'-dithiobis(2-nitrobenzoate), which forms disulfide bonds between the two subunits. Using polyacrylamide gel electrophoresis in sodium dodecyl sulfate we have shown that this crosslinking goes to completion over a wide range of protein concentration, ionic strength, and reagent concentration. Crosslinks are not formed in denaturing solvents such as sodium dodecyl sulfate and guanidine hydrochloride despite the fact that the same number of SH groups react as in the native state (2.3 +/- 0.2). The sedimentation coefficients of crosslinked and non-crosslinked samples are identical. Thus, crosslinks are formed between corresponding cysteines on different chains of the same molecule. This provides strong evidence for a model of chain interaction with both chains in register. Evidence has also been obtained that rabbit skeletal tropomyosin is composed only of alphaalpha and alphabeta subunits rather than a random mixture of chains.