bluuebunny/crossref_metadata_2025 huggingface dataset:
AKR Murine Leukemia Virus Genome: Frequency of Sequences in DNA of High-, Low-, and Non-Virus-Yielding Mouse Strains
Authors: Lowy Douglas R. , Chattopadhyay Sisir K. , Teich Natalie M. , Rowe Wallace P. , Levine Arthur S.
Published: May 2006

Studies with a single-stranded DNA probe complementary to the RNA of mouse-tropic AKR murine leukemia virus indicate that the complete genome of the AKR-type murine leukemia virus is present in the DNA of high- and low-virus-yielding mouse strains, while DNA of non-virus-yielding strains contains only a part of the genome. Furthermore, in those strains where the genome is complete, two populations of virus-specific DNA sequences can be identified (more abundant and less abundant species) according to their rate of association with the probe. Low-virus-yielding mouse strains contain fewer copies of the less abundant species and, consequently, fewer complete viral genomes than do high-virus-yielding strains. Thus, in the ten strains tested, there is a good correlation between completeness of the genome of AKR-type murine leukemia virus in cellular DNA and the capacity of the cells to release infectious AKR-type murine leukemia virus. Moreover, the number of complete viral genomes correlates with the frequency of infectious virus production by virus-positive strains. DNA from wild
Mus musculus
also contained viral sequences, the sample tested showing reassociation kinetics identical to the non-virus-producing strains.
Isolation of Exonuclease VIII: The Enzyme Associated with the
sbcA
Indirect Suppressor
Authors: Kushner Sidney R. , Nagaishi Haruko , Clark A. J.
Published: May 2006

recB
and/or
recC
deficiency in
Escherichia coli
K-12 is indirectly suppressed by the presence of
sbcA
-
mutations.
sbcA
-
strains contain an increased level of an ATP-independent nuclease. Genetic and enzymatic tests indicate that this activity is not exonuclease III, exonuclease V (
recB-recC
nuclease), DNA polymerase I, or lambda exonuclease. This new enzyme (exonuclease VIII) has been purified 750-fold and shows a striking preference for double-stranded DNA over heat-denatured DNA. It does not act endonucleolytically on closed circular, single-stranded DNA as exonuclease V does. It also lacks a 3′-phosphatase function. Analysis on sodium dodecyl sulfate-polyacrylamide gels indicates that exonuclease VIII is not present in unsuppressed (
sbcA
+
) strains. It is thought that
sbcA
determines some type of control function; the structural gene for exonuclease VIII is denoted by
recE
.
Inhibition of replication of normal adrenocortical cells in culture by adrenocorticotropin.
Authors: Ramachandran J , Suyama A T
Published: May 2006

Adrenocorticotropic hormone (ACTH) inhibited [3H]thymidine incorporation in normal adrenocortical cells of adult rats in culture, with a concomitant increase in corticosterone production and a characteristic retraction of cells. Both dibutyryl cyclic AMP and an analog of ACTH, which produces virtually no cyclic AMP, inhibited DNA synthesis and stimulated steroid production. ACTH inhibited the proliferation of adrenocortical cells obtained from suckling rats as well as the cells obtained from the capsular tissue of adult rat adrenal glands, whereas insulin caused a stimulation of DNA synthesis. These results suggest that the major role of ACTH is to induce the transformation of the undifferentiated cells of the adrenal gland into functional fasciculata cells and that the proliferation of adrenocortical cells may be under control of factors other than ACTH.
Steroidogenesis in rabbit preimplantation embryos.
Authors: Dickmann Z , Dey S K , Gupta J S
Published: May 2006

Rabbit preimplantation embryos were flushed from the reproductive tract at 24 hr (1- to 2-cell stage), 48 hr (morula), 72 hr (morula), 96 hr (blastocyst), 120 hr (blastocyst), and 144 hr (blastocyst) post coitum. At 168 hr (early postimplantation period), gestation sacs were excised, frozen, and sectioned in a cryostat. Delta5-3beta-Hydroxysteroid dehydrogenase [3(or 17)beta-hydroxysteroid:NAD(P) oxidoreductase, EC 1.1.1.51] activity was determined histochemically in whole preimplantation embryos and in sectioned postimplantation embryos. 3beta-Hydroxysteroid dehydrogenase activity began at 48 hr and was sustained through the late blastocyst stage (144 hr), with the exception of a brief drop, possibly cessation, of activity at 72 hr. There was no activity at 168 hr. Since 3 beta-hydroxysteroid dehydrogenase is a key enzyme in the metabolism of steroid hormones, its presence is strong evidence for steroidogenesis. Only 144-hr preimplantation embryos were used to determine 17 beta-hydroxysteroid dehydrogenase (estradiol-17beta:NAD 17-oxidoreductase, EC 1.1.1.62) activity, which was present, suggesting synthesis of estrogen. By means of radioimmunoassay, 144-hr preimplantation embryos were found to contain estradiol-17beta. Other authors have shown that rabbit blastocysts contain progesterone and other steroids, and these embryos can synthesize steroids from non-steroid and steroid precursors. Therefore, our results plus those of others prove that rabbit preimplantation embryos synthesize steroid hormones. Our present and previous results (with rats, hamsters, and mice) suggest that the steroid hormones synthesized by the embryo are critical for preimplantation embryogenesis and for implantation of the lbastocyst.
National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20014, USA.
Authors: Kraemer K H , Coon H G , Petinga R A , Barrett S F , Rahe A E , Robbins J H
Published: May 2006

Fibroblast strains from 12 patients with xeroderma pigmentosum had lower than normal rates of DNA repair, as determined by autoradiographic studies of ultraviolet-induced unscheduled nuclear DNA synthesis. The nuclei in binuclear cells, obtained by fusing fibroblasts from certain pairs of these strains, had a greater rate of DNA repair than the nuclei of either strain's unfused mononuclear cells. These results indicate that complementary corrections of the strains' repair defects had occurred in the fused cells. Four complementation groups were found, indicating that at least four mutations caused decreased DNA repair among these 12 strains. The unfused mononuclear cells of each group had a characteristic rate of repair that differed from the rates of the other groups.
Maximum-valence radii of transition metals
Authors: Pauling Linus
Published: May 2006

In many of their compounds the transition metals have covalence 9, forming nine bonds with use of nine hybrid
spd
bond orbitals. A set of maximum-valence single-bond radii is formulated for use in these compounds. These radii are in reasonably good agreement with observed bond lengths. Quadruple bonds between two transition metal atoms are about 50 pm (iron-group atoms) or 55 pm (palladium and platinum-group atoms) shorter than single bonds. This amount of shortening corresponds to four bent single bonds with the best set of bond angles, 79.24° and 128.8°.
Growth and differentiation in culture of leukemic leukocytes from a patient with acute myelogenous leukemia and re-identification of type-C virus.
Authors: Gallagher R E , Salahuddin S Z , Hall W T , McCredie K B , Gallo R C
Published: May 2006

Conditioned medium from a culture of whole human embryo cells stimulated prolonged exponential growth in suspension culture of leukocytes from a patient with acute myelogenous leukemia. Ten to 20% of the cultured cells consistently differentiated into mature granulocytes including neutrophils, eosinophils, and basophils. The proportion of lymphocytes declined after culturing, and tests for Epstein-Barr virus antigens were negative. An abnormality of a G group chromosome was observed in some metaphases from the patient's fresh bone marrow and from the cultured leukocytes, indicating growth in vitro of leukemic cells. After 4-10 weeks in culture, a budding type-C virus was continuously released by the cultured leukocytes, predominantly by undifferentiated blast cells. This virus was originally identified in three different cultures of a peripheral blood specimen obtained at the time of diagnosis. Subsequently, this virus was identified by reverse transcriptase (RNA-dependent DNA polymerase) assays and by electron microscopy in cultured leukocytes from a bone marrow specimen obtained 14 months later from the same patient. Virus produced by cultures of both specimens was closely related, if not identical, to the woolly monkey type-C virus.
Valence-bond theory of compounds of transition metals
Authors: Pauling Linus
Published: May 2006

An equation relating the strength (bondforming power) of an
spd
hybrid bond orbital to the angles it makes with other bond orbitals is formulated and applied in the discussion of the structures of transition-metal carbonyls and other substances by the valence-bond method. The rather simple theory gives results that agree well with those obtained by the complicated and laborious calculation of sets of orthogonal hybrid bond orbitals with maximum strength.
Kinetics of binding of carbon monoxide to lumbricus erythrocruorin: a possible model.
Authors: Giacometti G M , Focesi A , Giardina B , Brunori M , Wyman J
Published: May 2006

This paper represents a kinetic study of the binding of carbon monoxide by Lumbricus erythrocruorin. Observations on the quantum and the relaxation of the system both to equilibrium and to the steady state realized in the presence of constant illumination under various conditions are reported. The results, besides indicating the existence of at least two types of binding sites, give indications as to the behavior of a complex polyfunctional molecule, such as an enzyme, working under steady-state conditions.
Resonance Raman effect in mu-oxo-bis[iron(III) tetraphenylporphyrin].
Authors: Adar F , Srivastava T S
Published: May 2006

Resonance Raman spectra of mu-oxo-bis[iron(III) tetraphenylporphyrin] have been observed and compared to Raman spectra of the monomers iron(III) tetraphenylporphyrin chloride and bis(piperidine)iron(II) tetraphenylporphyrin. Selection rules for the Raman effect under conditions of resonance of the incident photons with electronic states are presented for the exact symmetry group (C2) and the pseudo-symmetry group (D4d): emphasis is placed on the physical processes involved in scattering via vibronic states of the dimer. These two models are experimentally distinguishable in the behavior of the depolarization ratios of the dimer vibrational doublets. Experimental data favor the assignment of D4d as the symmetry group relevant to a description of the various states of the dimer. The usefulness of resonance Raman spectra of the mu-oco-dimer of Fe(III) tetraphenylporphyrin has been discussed with respect to several biochemical systems where there is strong evidence of two or more closely interacting chromophores.
Chemical induction of sperm abnormalities in mice.
Authors: Wyrobek A J , Bruce W R
Published: May 2006

The sperm of (C57BL X C3H)F1 mice were examined 1, 4, and 10 weeks after a subacute treatment with one of 25 chemicals at two or more dose levels. The fraction of sperm that were abnormal in shape was elevated above control values of 1.2-3.4% for methyl methanesulfonate, ethyl methanesulfonate, griseofulvin, benzo[a]pyrene, METEPA [tris(2-methyl-l-aziridinyl)phosphine oxide], THIO-TEPA [tris(l-aziridinyl)phosphine sulfide], mitomycin C, myleran, vinblastine sulphate, hydroxyurea, 3-methylcholanthrene, colchicine, actinomycin D, imuran, cyclophosphamide, 5-iododeoxyuridine, dichlorvos, aminopterin, and trimethylphosphate. Dimethylnitrosamine, urethane, DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane], 1,1-dimethylhydrazine, caffeine, and calcium cyclamate did not induce elevated levels of sperm abnormalities. The results suggest that sperm abnormalities might provide a rapid inexpensive mammalian screen for agents that lead to errors in the differentiation of spermatogenic stem cells in vivo and thus indicate agents which might prove to be mutagenic, teratogenic, or carcinogenic.
Guanosine metabolism and regulation of fruiting body construction in dictyostelium discoideum.
Authors: Cohen A , Sussman M
Published: May 2006

A cell aggregate of Dictyostelium discoideum either constructs a fruiting body directly or transforms into a migrating slug and fruits later on in some other locale. In the presence of formycin B, an inosine analog, and in an environment that otherwise favors fruiting, aggregates having reached a relatively late (17 hr) stage of fruit construction abandon that program and transform into migrating slugs. They then revert to the fruiting mode and construct normal fruiting bodies without further interference [Brackenbury et al. (1974) J. Mol. Biol. 90, 529-539]. The data presented here suggest that formycin B exerts its morphogenetic effect by interfering competitively with the metabolism of guanosine. Thus: see article. The recovery from formycin B is thought to result from the ensuing accumulation of guanosine and reversal of the inhibition. In support of this are the following: (1) Formycin B does cause, in vivo, an accumulation of guanosine. Exogenoug guanosine reverses the effect of formycin B, depending on their relative concentrations. (2) Guanosine is phosphorylitically cleaved to guanine and ribose-1-P by purine ribonucleoside phosphorylase (purine-nucleoside:orthophosphate ribosyl transferase, EC 2.4.2.1), present in D. discoideum extracts, and formycin B is a competitive inhibitor or this reaction with a very high affinity for the enzyme. (3) Four other analogs, also competitive inhibitors of this enzyme, produce precisely the same morphogenetic deviation. The concentrations required are consistent with the relative K1 values.
Effect of temporal fluctuation of selection coefficient on gene frequency in a population.
Authors: Takahata N , Ishii K , Matsuda H
Published: May 2006

The diffusion equations describing the change of gene frequencies are extended to indlude the effect of temporal fluctuation of selection coefficient that may persist for some generations. The equilibrium distribution of gene frequencies and the fixation probability of a mutant gene are obtained from the extended equations. Comparison is made with the experimental data on protein polymorphism. A possible bearing of the fluctuation of selection coefficient on the problem of molecular evolution is discussed in relation to the neutral theory.
Strand-selective transcription of globin genes in rabbit erythroid cells and chromatin.
Authors: Wilson G N , Steggles A W , Nienhuis A W
Published: May 2006

In order to investigate the symmetry of globin gene transcription, complementary RNA (cRNA) was synthesized using rabbit globin complementary DNA (cDNA) as a template for Escherichia coli DNA-dependent RNA polymerase (RNA nucleotidyltransferase). The cRNA hybridized specifically to its own cDNA template but not to sheep cDNA, rabbit globin mRNA, or poly(dT). Hybridization studies with cRNA demonstrated that RNA sequences transcribed from the DNA strand complementary to the globin gene region (anti-strand) were not present in cellular, total nuclear, or fractionated nuclear RNA from rabbit marrow. Such sequences were detected in RNA transcribed from rabbit marrow chromatin by E. coli or sheep liver RNA polymerases, but amounted to less than 50% of the globin mRNA sequences present in the same transcript. The evidence indicates that globin mRNA transcription is predominantly DNA strand specific.
Structural requirements for time-dependent inhibition of prostaglandin biosynthesis by anti-inflammatory drugs.
Authors: Rome L H , Lands W E
Published: May 2006

Several anti-inflammatory drugs have been examined for their ability to cause a time-dependent destruction of the fatty acid oxygenase that produces prostaglandins. All of the time-dependent inhibitors contained carboxylic acid moieties, and in addition all but one of the drugs contained a halogen atom. Structural analogs (of the time-dependent inhibitors) lacking halogen atoms were unable to cause a time-dependent destruction of the enzyme. The time-dependent property of an inhibitor was totally eliminated after methylation of the carboxylate group. Methylation did not, however, alter the ability of the inhibitors to competitively inhibit the oxygenase. Thus, the reversible binding of the agents at the active site was not appreciably dependent upon the free carboxyl group, whereas the subsequent irreversible process was.
Selective killing of transformed baby hamster kidney (BHK) cells.
Authors: Pardee A B , James L J
Published: May 2006

We report here that certain drugs can protect Syrian baby hamster kidney cells (BHK) in culture against the lethal agents cytosine arabinonucleoside, hydroxyurea, and colcemid. Polyoma virus-transformed BHK cells (PyBHK) are killed under the same conditions. The protective drugs include caffeine and streptovitacin A. Kinetic studies show that these drugs act specifically in G1, and that they shift BHK cells from G1 into the G0 state at the restriction point, similar to the effects of high cell density or serum deprivation. These drugs do not block the growth of PyBHK cells nearly as effectively, consistent with a reduced effectiveness of restriction point control in virus-transformed cells. Consequently, the transformed cells around their cycle and are killed by the cell cycle phase-specific toxic agents, in contrast to the arrested BHK cells. These findings provide a model for studies on differential killing of tumor versus normal cells in vivo.
On the mechanism of cytolysis by complement: evidence on insertion of C5b and C7 subunits of the C5b,6,7 complex into phospholipid bilayers of erythrocyte membranes.
Authors: Hammer C H , Nicholson A , Mayer M M
Published: May 2006

The doughnut hypothesis of cytolysis by complement [Mayer, M. M. (1972) Proc. Nat. Acad. Sci. USA 69, 2954-2958] describes an annular structure made up of C5b-9 (complement factors C5b, C6, C7, C8, and C9) which becomes inserted in the lipid bilayer of the cell membrane, thus creating a hole. We now present initial explorations of this hypothesis. EAC1-6 and EAC1-7 (sheep erythrocytes carrying rabbit antibody and complement factors C1 through C6 or C1 through C7, respectively), prepared with either 125I-C3 or 125I-C5 were incubated with trypsin and the release of bound 125I was measured. In the case of 125I-C3, all of the radioactivity was released by trypsin from both intermediates. With 125I-C5, trypsin released all of the 125I from EAC1-6, but only 40-55% from EAC1-7. Possible reasons for resistance of the C5b subunit in EAC1-7 to tryptic digestion are discussed; in terms of the doughnut hypothesis it would be due to shielding by lipid molecules as a consequence of insertion into the lipid bilayer. In accord with this interpretation we have also found that C5b in EAC1-7, but not in EAC1-6, resists elution by 0.3 M NaC1. Similarly, we have found that 125I-C7 in EAC1-7 resists stripping by trypsin. Hence, we now propose the hypothesis that hydrophobic polypeptide chains from the C5b and the C7 subunits of C5b,6,7 complex become inserted in the phospholipid bilayer and that subsequent reactions with C8 and C9 open a channel across the membrane.
Murine leukemia virus: detection of unintegrated double-stranded DNA forms of the provirus.
Authors: Gianni A M , Smotkin D , Weinberg R A
Published: May 2006

Infection of JLS V-9 (mouse bone marrow) cells with Moloney murine leukemia virus leads to appearance of virus-specific DNA in the low molecular weight DNA fraction from infected cells. Most of this DNA is double-stranded. Two discrete forms of double-stranded DNA, both of molecular weight 6 times 10-6, have been characterized. One of these forms is closed-circular, supercoiled DNA; the other form is a mixture of nicked-circular and linear DNA.
Abnormal collagen metabolism in cultured cells in osteogenesis imperfecta.
Authors: Penttinen R P , Lichtenstein J R , Martin G R , McKusick V A
Published: May 2006

Cells obtained from normal human skin synthesize predominantly type I collogen in culture. Cells obtained from the skin of an infant with a severe form of osteogenesis imperfecta were found to synthesize as much type III as type I collagen. Decreased synthesis of type I collagen could explain the tissue fragility observed in this case.
Nerve growth factor induces volume increase and enhances tyrosine hydroxylase synthesis in chemically axotomized sympathetic ganglia of newborn rats.
Authors: Levi-Montalcini R , Aloe L , Mugnaini E , Oesch F , Thoenen H
Published: May 2006

Concomitant daily treatment of newborn rats for a 2-week to 1-month period with 10 mug/g of body weight of nerve growth factor and 100 mug/g of body weight of 6-hydroxydopamine produces in the cell bodies of adrenergic neurons the characteristic effects of the growth factor but in the nerve terminals the characteristic effects of 6-hydroxydopamine. The dual opposite effects result in a striking volume increase of sympathetic ganglia which far exceeds that produced by nerve growth factor alone. The selective induction of tyrosine hydroxylase [L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] in these chemically axotomized adrenergic neurons is even more pronounced than that produced by nerve growth factor alone in intact neurons.
Ultrastructural localization of tyrosine hydroxylase in noradrenergic neurons of brain.
Authors: Pickel V M , Joh T H , Reis D J
Published: May 2006

Tyrosine hydroxylase (EC 1.14.16.2), the enzyme catalyzing the rate-limiting step in catecholamine biosynthesis, was localized by electron microscopy within noradrenergic neurons of the nucleus locus coeruleus of the rat brain with a specific antibody to tyrosine hydroxylase labeled by the peroxidase-antiperoxidase immunohistochemical method. Labeled cell bodies and their processes were easily distinguished from unstained neuronal elements in the neuropil. The hydroxylase was only seen in the neuronal cytoplasm. Its distribution in processes was different from that in cell soma. In longitudinal sections of axons and dendrites, the peroxides reaction product appeared as fiber-like strands aligned parallel with the plasma membrane. In cross section, the labeled structures had a diameter of 220 A and exhibited an orderly distribution within the processes. The size and distribution of the peroxidase-stained structures suggest that they are neurotubules. In the perikarya, the cytoplasm was diffusely stained; the reaction was most intense on membranes of endoplasmic reticulum and Golgi apparatus, whereas lysosomes and mitochondria did not stain. The ultrastructural localization of tyrosine hydroxylase is consistent with biochemical data suggesting that the enzyme exists in different states in cell body and processes. The ultrastructural identification of enzymes subserving synthesis of neurotransmitters in central neurons and their processes may provide a useful tool in mapping the distribution of chemically specific synapses on identifiable neurons in brain.
Structure of a soluble super-active insulin is revealed by the nature of the complex between cyanogen-bromide-activated sepharose and amines.
Authors: Wilchek M , Oka T , Topper Y J
Published: May 2006

Insulin-like material with elevated insulin specific acitivity is released from insulin-Sepharose in the presence of bovine-serum albumin. The mechanism of release and the chemical nature of this insulin-like material are revealed by the finding that amine-Sepharose is O-Sepharose-N-substituted isourea. Nucleophilic attack by amino groups releases N-1-N-2-disubstituted guanidines. Correspondingly, it is shown that the super-active insulin-like material is an N-1-N-2-disubstituted guanidine in which insulin and bovine-serum albumin are the substituents.
Possible relationship of poly(A) shortening to mRNA turnover.
Authors: Sheiness D , Puckett L , Darnell J E
Published: May 2006

Whereas the original size of poly(A) in HeLa cells is about 200 nucleotides, at steady state most of the poly(A) in mRNA contains less than 50 nucleotides. An endonucleolytic attack on poly(A) is suggested as the most likely method to accumulate short pieces of poly(A). Both poly(A) shortening and mRNA turnover appear to be inhibited by emetine, a drug that stops translation. It is possible that a random endonucleolytic attack leads to scission of poly(A) to a size below which the mRNA is unstable.
Gibberellic-Acid-Induced Cell Elongation in Lettuce Hypocotyls
Authors: Srivastava L. M. , Sawhney V. K. , Taylor I. E. P.
Published: May 2006

Gibberellic acid (10 μM) causes lettuce hypocotyl cells to elongate by 400-500% more than water controls in 72 hr. Kinetic data indicate that whereas in water controls cell elongation occurs between 24 and 48 hr, in gibberellic-acid-treated material it starts at 8 hr and continues to 72 hr. Dry weight of the cell wall shows a corresponding increase with cell elongation. Two-hour pulse labeling with [
14
C]glucose, however, indicates a peak in the incorporation of label in the wall fraction at 8 hr, when growth has only just begun, and a progressive decline later, when elongation is occurring at maximum rate. The peak coincides with extensive dictyosomal activity, proliferation of endoplasmic reticulum and polyribosomes, and connections between the endoplasmic reticulum and plasmalemma in both water- and gibberellic-acid-treated hypocotyls. At later times, the cells contain only a thin layer of cytoplasm and no special cytological features are observed. These observations indicate that, although cell growth in lettuce hypocotyls is accompanied by wall synthesis, nevertheless the cells undergo their most rapid polysaccharide and protein synthesis
prior
to extension growth. They also explain the earlier reported ”enhanced sensitivity” of lettuce hypocotyls to gibberellic acid application at 8 hr after the beginning of the experiment.
Localization of RNA from heat-induced polysomes at puff sites in Drosophila melanogaster.
Authors: McKenzie S L , Henikoff S , Meselson M
Published: May 2006

Heat treatment of D. melanogaster tissue culture cells causes drastic changes in the pattern of protein synthesis and the size distribution of polysomes. Like the heat shock puffs on polytene chromosomes which appear while preexisting puffs regress, heat shock proteins appear on gels while the synthesis of preexisting proteins is sharply reduced, and heat-induced polysomes appear on gradients after preexisting polysomes have disappeared. Most of the poly(adenylic acid)-containing RNA isolated from high-temperature polysomes sediments in sucrose gradients and migrates in gels as a rather narrow band. This RNA is of sufficient size to code for one particular protein that is found to account for more than half of the total synthesis at high temperature. The RNA hybridizes in situ mainly at chromosome sub-division 87B, the site of the major heat shock puff.
Plasminogen-independent fibrinolysis by proteases produced by transformed chick embryo fibroblasts.
Authors: Chen L B , Buchanan J M
Published: May 2006

The fibrinolytic activity of proteases secreted by chick embryo fibroblasts infected with Rous sarcoma virus was studied by use of a procedure in which a fibrin clot was formed with highly purified fibrinogen and thrombin above the cell layer. This procedure results in the formation of fibrin that is apparently a more suitable substrate for studies on fibrinolysis than is fibrin prepared by other methods. Since neither plasminogen nor serum were included in the assay system in the present studies, the fibrinolytic activity observed cannot be ascribed to the conversion of the plasminogen in serum to plasmin by a plasminogen activator produced by transformed cells. Our procedure, therefore, measures proteolytic activities other than those reported by previous investigators. Maintenance of some of the transformed phenotypes of Rous sarcoma virus transformed chick embryo fibroblasts such as morpholigical change and increased rate of glucose uptake apparently does not depend on the presence of plasminogen in the culture medium.
Activation by cyclic 3':5'-adenosine monophosphate of tyrosine hydroxylase in the rat brain.
Authors: Harris J E , Baldessarini R J , Morgenroth V H , Roth R H
Published: May 2006

Membrane-permeable derivatives of cyclic AMP (cAMP) produced concentration-dependent increases in activity of tyrosine hydroxylase (L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2) in membrane-limited nerve endings (synaptosomes) prepared from three regions of rat brain. Increased hydroxylation occurred even after preincubation and removal of dibutyryl cyclic AMP. In all brain regions, the hydroxylation of phenylalanine and tyrosine was increased, but dibutyryl cAMP had little effect on activity of tryptophan hydroxylase, no effect on aromatic amino-acid decarboxylase, on uptake of tyrosine or phenylalanine, uptake or efflux of dopamine, or distribution of hydroxylase between cytoplasmic and particulate components of the synaptosomes. Dibutyryl cAMP decreased inhibition of catecholamine synthesis in synaptosomes by dopamine and apomorphine. In a soluble preparation of striatal tyrosine hydroxylase, activity was increased by addition of lower concentrations of cAMP or dibutyryl cAMP than with unbroken nerve endings, when subsaturating concentrations of tyrosine and cofactor were employed, while butyrate, chloride, 5'-AMP, ADP, ATP, and cyclic GMP had no activating effect. Increased activity of soluble tyrosine hydroxylase was reflected in increased affinity (Km) for substrate and cofactor and decreased affinity (Ki) for inhibitory end-product (dopamine), suggesting a change in the physical-chemical state of the enzyme or an activator molecule. Cyclic AMP may activate tyrosine hydroxylase during periods of increased neuronal activity.
Preparation of large monodomain phospholipid bilayer smectic liquid crystals.
Authors: Powers L , Clark N A
Published: May 2006

A technique for the preparation of large monodomain phospholipid bilayer arrays is described. Evidence for the monodomain nature of the samples, obtained from optical birefringence, light scattering, and x-ray diffraction experiments, is presented.
A new approach to empirical intermolecular and conformational potential energy functions. II. Applications to crystal packing, rotational barriers, and conformational analysis.
Authors: Burgess A W , Shipman L L , Scheraga H A
Published: May 2006

An empirical potential energy function based on the interactions of electrons and nuclei (EPEN) has been tested on molecules other than those used for its parameterization. The results indicate that this energy function is able to predict reliably the lowest energy conformations, the potential energy differences between conformations, rotational barrier heights, and dipole moments for a series of alkanes, amines, alcohols, and carbohydrates. Crystal packing studies on n-hexane, n-octane, methylamine, methanol, and alpha-d-glucose, using this same potential, indicate that it is also reliable for calculating intermolecular interaction energies and low-energy orientations.
Epithelial cell death and cyclic AMP increase during palatal development.
Authors: Pratt R M , Martin G R
Published: May 2006

Cyclic AMP levels increase abruptly in the secondary palatal shelf (mesenchyme plus a two- to three-cell-layered epithelium) between day 15 and 16 of gestation in the rat embryo. The addition of dibutyryl cyclic AMP to the media in which immature palatal shelves (day 14) are cultured causes a precocious decrease in DNA synthesis, but increased glycoprotein synthesis and epithelial adhesiveness. These changes are most evident in the medial-edge epithelial cells and resemble the developmental events that occur normally on day 15 and 16 during formation of the secondary palate. The initiation of epithelial cell death and adhesiveness in the medial edge of the palatal shelf may be mediated through an increase in cyclic AMP.
Biochemical method for mapping mutational alterations in DNA with S1 nuclease: the location of deletions and temperature-sensitive mutations in simian virus 40.
Authors: Shenk T E , Rhodes C , Rigby P W , Berg P
Published: May 2006

S1 nuclease (EC 3.1.4.X), a single-strand-specific nuclease, can be used to accurately map the location of mutational alterations in simian virus 40 (SV40) DNA. Deletions of between 32 and 190 base pairs, which are at or below the limit of detectability by conventional electron microscopic analysis of heteroduplex DNAs, have been located in this way. To map a deletion, a mixture of unit length, linear DNA, prepared from the SV40 deletion mutant and its wild-type parent, are denatured and reannealed to form heteroduplexes. S1 nuclease can cut such heteroduplexes at the nonbase-paired region to produce fragments whose lengths correspond to the position of the deletion. Similarly, specific fragments are produced when S1 nuclease cleaves a heteroduplex formed from the DNAs of SV40 temperature-sensitive mutants and either their revertants or wild-type parents. Thus, the positions of the nonhomology between these DNAs can be determined.
Patterns of organization of actin and myosin in normal and transformed cultured cells.
Authors: Pollack R , Osborn M , Weber K
Published: May 2006

The patterns of distribution of intracellular actin and myosin were examined by specific immunofluorescence in a series of normal, simian-virus-40-transformed, and revertant cell lines of rat and mouse origin. A consistent correlation was found between sensitivity to anchorage-dependent growth control and the presence of large, thick sheaths of actin-containing material. The presence of these sheaths was temperature-dependent in a rat line transformed by a temperature-sensitive mutant in the complementation group A of the oncogenic virus simian virus 40.
Cyclic AMP modulates microvillus formation and agglutinability in transformed and normal mouse fibroblasts.
Authors: Willingham M C , Pastan I
Published: May 2006

We have utilized dark field microscopy to observe the surface microstructure of living cultured cells. Using this method, we have found that dibutyryl cAMP treatment causes regression of the numerous, long cell surface microvilli present on L929 cells. Thirty minutes after removal of dibutyryl cAMP, microvilli reappear. An inhibitor of phosphodiesterase (methylisobutylxanthine) and a stimulator of adenylate cyclase (prostaglandin E1), both of which raise cAMP levels, cause regression of microvilli in 15 min. Untransformed 3T3 cells show very few microvilli when viewed still attached to their substratum or after removal with EDTA. Treatment of these cells with trypsin causes the formation of numerous microvilli on their surface. When clumps of cells agglutinated by concanavalin A are examined by thin section electron microscopy, the cells are seen to be held together by a "forest" of interdigitating microvilli and only rarely is there apposition of the areas of membrane between microvilli. At the same time the distribution of surface-bound concanavalin A was examined using immunofluorescent light microscopy, and concanavalin A was found to be uniformly distributed over the cell surface. We propose that agglutinability of mouse and rat fibroblasts is regulated through the modulation of cell surface microvilli by cAMP, and that transformed cells are highly agglutinable because their low cAMP levels result in the formation of numerous surface microvilli.
Histone-histone propinquity by aldehyde fixation of chromatin.
Authors: Chalkley R , Hunter C
Published: May 2006

Histones have been fixed within the chromatin complex using either formaldehyde or glutaraldehyde. Evidence is presented which argues that in short time periods formaldehyde fixation leads to the formation of reversible covalent bonds between histone and DNA.On the other hand, fixation of chromatin with glutaraldehyde leads initially to the formation of polymers of F1 histone, and at a later stage of multiple small oligomers of the remaining histones. There oligomers then increase in size until they become too large to detect by polyacrylamide gel electrophoresis. Exclusive formation of histone dimers or tetramers was not observed. The simplest model for histone distribution on DNA which encompasses these observations is one in which histones are organized as a fairly extensive linear overlapping array.
Macromolecular enzymatic product of NAD+ in liver mitochondria.
Authors: Kun E , Zimber P H , Chang A C , Puschendorf B , Grunicke H
Published: May 2006

Rat liver mitochondria contain a Mg2+-requiring system that transfers the ADP-ribose moiety of NAD+ to an acceptor protein. The enzyme system was extracted in a soluble form and the ADP-ribosylated protein product was isolated by hydroxyapatite and Sephadex chromatography. The ADP-ribosylated protein product has a molecular weight of 100,000 and can be dissociated into subunits of 50,000 daltons by sodium dodecyl sulfate gel electrophoresis. Incubation of the isotopically labeled ADP-ribosylated protein with nicotinamide and a mitochondrial extract yields labeled NAD+, indicating apparent reversibility of the reaction. Enzymatic degradation of the ADP-ribosylated protein with snake venom phosphodiesterase liberates AMP and ADP-ribose or its isomer. Identification of these products and reversibility of the reaction show that the ADP-ribose moiety of NAD+ is the molecular species that is transferred to the acceptor protein. A fraction of the protein-bound ADP-ribose appears to be present as an an oligomer. The enzymatic protein-ADP-ribosylating reaction is inhibited by nicotinamide, ADP-ribose, the fluorophosphate of AMP, and picrylsulfonic acid.
Magnetic resonance spectra of membranes.
Authors: Brûlet P , McConnell H M
Published: May 2006

A number of electron and nuclear magnetic resonance studies of model membranes, and biological membranes, involve time-dependent magnetic interactions diffusion relative to one another. The two-dimensional character of this motion can have a special, large effect on magnetic resonance line shapes, and relaxation rates, because of the long-time tail of the correlation function for magnetic interactions modulated by this motion. Equations are given for the specific case in which nuclear relaxation rates are enhanced due to dipolar interactions with membrane-bound spin labels. An experimental study of spin-label-enhanced 13-C nuclear relaxation in unsonicated dispersions of phosphatidylcholine is accounted for with this theory, together with the previously reported lipid diffusion constant of D congruent to 2 times 10- minus 8 cm-2/sec. Our analysis of previously reported 1-H and 13-C nuclear relaxation rates in small phospholipid vesicles produced by sonication suggests that the rate of lateral diffusion in these small vesicles may be significantly larger than 10- minus 8 cm-2/sec.
A group of thermodynamic potentials applicable to ligand binding by a polyfunctional macromolecule.
Authors: Wyman J
Published: May 2006

The binding of ligands by a macromolecule can be well described by a group of potentials derivable from the energy and of which the original binding potential is one. The group is Abelian and is isomorphic with a group of symmetries. Each member corresponds to a particular set of experimental conditions--system open to some, closed to others, of the ligand-and the group as a whole is an immediate source of all possible linkage relations applicable to the macromolecule. Seen in terms of information theory it can be interpreted as a program for the response of the macromolecule to its ligands according to the conditions with which it is faced. The group provides a ready formulation of the effect of a ligand on the equilibrium constant for a reaction involving a set of macromolecules, and it leads to a clear-cut distinction between true and pseudolinkage.
Cell cycle specific fluctuations in adenosine 3':5'-cyclic monophosphate and polyamines of Chinese hamster cells.
Authors: Russell D H , Stambrook P J
Published: May 2006

Chinese hamster V79 cells were synchronized by mitotic selection, which resulted in approximately 95% synchrony. The adenosine 3':5'-cyclic monophosphate level was elevated within 3 hr (G1 phase) and reached a level 2-fold higher than in early G1 within 6 hr (early S phase). An increase in ornithine decarboxylase activity (6-ornithine carboxy-lyase, EC 4.1.1.17), the initial enzyme in the polyamine biosynthetic pathway, was detected within 4 hr and was maximal at 8 hr. Since about 20% of the cells were labeled with [3-H]thymidine at 4 hr, ornithine decarboxylase exhibits cell-cycle specific activity starting in late G1 and continuing through middle S phase. The activity of S-adenosylmethionine decarboxylase (S-adenosyl-L-methionine carboxylase, EC 4.1.1.50) increased within 5 hr, i.e., early S phase. It is suggested on the basis of these data and other studies discussed herein that the increase in ornithine decarboxylase activity, which parallels closely the elevation in cyclic AMP, is an example of adenosine 3':5'-cyclic monophosphate-mediated protein synthesis.
Nuclear magnetic resonance spectroscopy: reinvestigation of carbon-13 spin-lattice relaxation time measurements of amino acids.
Authors: Pearson H , Gust D , Armitage I M , Huber H , Roberts J D , Stark R E , Vold R R , Vold R L
Published: May 2006

The carbon-13 spin-lattice relaxation times (T1) of glycine have been measured as a function of pD and concentration. Contrary to previously reported findings, no significant dependence was observed on either pD or concentration. In addition, the T1 values reported here are much longer than those published earlier. The discrepancies arise from the presence of paramagnetic impurities in the earlier samples. For the carboxyl carbon, dipole-dipole relaxation is dominant in both D2O and H2O solution, and in H2O there is a significant intermolecular dipolar contribution. Proton and oxygen relaxation times have also been measured. These, along with the carbon relaxation data, allow a discussion of the dynamics of glycine in solution.
Interaction of glyoxal and methylglyoxal with biogenic amines.
Authors: Szent-Györgyi A , McLaughlin J A
Published: May 2006

Glyoxal and methylglyoxal interact with biogenic amines and form biologically active free radicals. Electron spin resonance absorption of the radical at room temperature is characterized by a signal at g equals 2.004 with peak-to-peak width of 29 G. An optical absorption at 400 nm with molar absorptivity of 23,000 accompanies the formation of the radical. The dry powdered preparation of the same reaction, which is considered to be the seconardy product, gives an electron spin resonance signal much narrower and 1/200 in intensity compared with the one in solution. Similarly the 400 nm absorption intensity is 1/8 that of the primary product. Possible biological significance of the primary and the secondary product, in relation to muscular dystrophy and photophosphorylation, is discussed.
Amino-acid sequence of bovine carboxypeptidase B.
Authors: Titani K , Ericsson L H , Walsh K A , Neurath H
Published: May 2006

The amino-acid sequence of bovine carboxypeptidase B [peptidyl-L-lysine(-L-arginine)hydrolase, EC 3.4.12.3] has been determined using the heavy and light chains of the enzyme isolated from spontaneously activated pancreatic juice. Comparison of the sequence with that of carboxypeptidase A shows that the two enzymes are homologous (49% identity) and that all but one of the functional residues identified in carboxypeptidase A occur in corresponding loci in carboxypeptidase B (peptidyl-L-amino acid hydrolase, EC 3.4.12.2). The exception is the replacement of Ile-255 at the bottom of the substrate binding pocket of carboxypeptidase A, by aspartic acid in carboxypeptidase B. This single change can account for the difference in specificity of the two enzymes.
Lipoteichoic acid: a specific inhibitor of autolysin activity in Pneumococcus.
Authors: Höltje J V , Tomasz A
Published: May 2006

The choline-containing pneumococcal lipoteichoic acid (Forssman antigen) is a powerful inhibitor of the homologous autolytic enzyme, an N-acetylmuramyl-L-alanine amidase (EC 3.5.1.28, MUCOPEPTIDE AMIDOHYDROLASE). Low concentrations of deoxycholate can reverse the inhibition. Wall teichoic acid preparations are inactive at several hundred-fold higher concentrations. Activation of an inactive form of autolysin by in vitro incubation with choline-containing cell walls is also inhibited by lipoteichoic acid. Addition of lipoteichoic acid to the growth medium of pneumococcal cultures causes chain formation, resistance to stationary phase lysis, and penicillin tolerance. It is suggested that a physiological role of lipoteichoic acids may be in the in vivo control of autolysin activity.
Growth of mouse megakaryocyte colonies in vitro.
Authors: Metcalf D , MacDonald H R , Odartchenko N , Sordat B
Published: May 2006

Mouse bone marrow and spleen cells formed pure or mixed colonies of up to 80 megakaryocytes in agar cultures after stimulation by medium conditioned by activated mouse lymphoid cells. Megakaryocytes were identified on the basis of their morphology, polyploid mitoses and DNA content, and high cytoplasmic content of acetylcholinesterase. Megakaryocyte colony-forming cells were relatively small with a peak sedimentation velocity of 4.2 mm/hr. Spleen, lymph node, and thymus cells produced the factor stimulating megakaryocyte proliferation after culture in medium containing 2-mercaptoethanol, with or without added mitogens or allogeneic spleen cells. Peak activity in conditioning medium was associated with the small lymphocyte fractions in mouse spleen.
Human X-Linked genes regionally mapped utilizing X-autosome translocations and somatic cell hybrids.
Authors: Shows T B , Brown J A
Published: May 2006

Human genes coding for hypoxanthine phosphoribosyltransferase (HPRT, EC 2.4.2.8; IMP:pyrophosphate phosphoribosyltransferase), glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49; D-glucose-6-phosphate:NADP+ 1-oxidoreductase), and phosphoglycerate kinase (PGK, EC 2.7.2.3; ATP:3-phospho-D-glycerate 1-phosphotransferase) have been assigned to specific regions on the long arm of the X chromosome by somatic cell gentic techniques. Gene assignment and linear order were determined by employing human somatic cells possessing an X/9 translocation or an X/22 translocation in man-mouse cell hybridization studies. The X/9 translocation involved the majority of the X long arm translocated to chromosome 9 and the X/22 translocation involved the distal half of the X long arm translocated to 22. In each case these rearrangements appeared to be reciprocal. Concordant segregation of X-linked enzymes and segments of the X chromosome generated by the translocations indicated assignment of the PGK gene to a proximal long arm region (q12-q22) and the HPRT and G6PD genes to the distal half (q22-qter) of the X long arm. Further evidence suggests a gene order on the X long arm of centromere-PGK-HPRT-G6PD.
Tertiary structure of myohemerythrin at low resolution.
Authors: Hendrickson W A , Klippenstein G L , Ward K B
Published: May 2006

X-ray diffraction studies have produced a low resolution image and also located the iron atoms of a monomeric hemerythrin from muscles of a sipunculan worm. These results reveal the course of the polypeptide chain and some details of the active center.