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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

ATP and UTP support microtubule assembly through the action of brain nucleoside-5'-diphosphate kinase on GDP. Penningroth and Kirschner (1977) J. Mol. Biol. 115, 643-673) have proposed that microtubule assembly may occur by either of two mechanisms: indirectly, through nucleoside-5'-diphosphate kinase-catalyzed phosphorylation of uncomplexed GDP and directly by nucleoside-5'-diphosphate kinase-mediated transphosphorylation of tubulin-bound GDP at low tubulin concentrations. We find the rates of GDP and GTP release (0.68 and 0.32 min-1, respectively) are sufficiently fast relative to assembly to permit GDP release, phosphorylation, and GTP binding as the sole mechanism of nucleoside-5'-diphosphate kinase action in microtubule assembly. Computer simulation studies accord with the conclusion that GDP release is rapid relative to microtubule assembly. The specific activity of the nucleoside-5'-diphosphate kinase is 1.7 nmol/min/mg of microtubular protein under the conditions studied. Pulse-chase experiments with tubulin . [14C]GDP complex and the rapidity of GDP phosphorylation by the kinase are in agreement with this scheme. Finally, it was observed that the extent and rate of microtubule assembly depends upon the [ATP]/[ADP] ratio.
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PMID:Nucleotide release from tubulin and nucleoside-5'-diphosphate kinase action in microtubule assembly. 22 18

Mutants in the spo T gene have been isolated as stringent second site revertants of the relC mutation. These show varying degrees of the characteristics associated with the spoT1 gene, viz relative amount and absolute levels of both pppGpp and ppGpp and the decay rate of the latter. The entry of 3H-guanosine into GTP and ppGpr pools in spoT+ and spoT1 cells either growing exponentially or during amino acid starvation was determined, and the rate of ppGpp synthesis and its decay constant calculated. During exponential growth the ppGpp pool is 2-fold higher, its decay constant 10-fold lower, and its synthesis rate 5-fold lower in spoT- than in spoT+ cells; during amino acid starvation the ppGpp pool is 2-fold higher, its decay constant 20-fold lower, and its synthesis rate 10-fold lower in spoT than in spoT+ cells. In one of the "intermediate" spoT mutants the rate of entry of 3H-guanosine into GTP, ppGpp and pppGpp was measured during amino acid starvation. The data form the basis of a model for the interconversion of the guanosine nucleotides in which the flow is: GDP leads to GTP leads to pppGpp leads to ppGpp leads to Y. Calculations of the rates of synthesis and conversion of pppGpp and ppGpp under various conditions in various spoT+ and spoT- strains indicate that the ppGpp concentration indirectly controls the rate of pppGpp synthesis.
Mol Gen Genet 1977 Jan 07
PMID:Interaction of alleles of the relA, relC and spoT genes in Escherichia coli: analysis of the interconversion of GTP, ppGpp and pppGpp. 31 45

Kinetics of accumulation and degradation of ppGpp and pppGpp were analysed in spoT+ and spoT strains of Escherichia coli. The experimental data in this paper indicate that on degradation ppGpp is not converted to pppGpp but instead is converted to GDP which is in turn phosphorylated to GTP. In addition the data are consistent with the idea the pppGpp is a direct precursor of ppGpp. We propose that ppGpp is metabolised according to the following pathway: GTP-pppGpp--ppGpp--GDP--GTP, which we call the ppGpp cycle. Coupled with the observations in spot strains we assume that ppGpp blocks its own synthesis by inhibiting the synthesis of pppGpp but not the interconversion of the two nucleotides.
Mol Gen Genet 1977 Feb 15
PMID:ppGpp cycle in Escherichia coli. 32 33

The two species of Elongation Factor Tu coded for by the tufA and tufB genes were synthesized in UV-irradiated E coli infected by transducing phages bearing the separate genes. Both proteins interact similarly with EFTs, GDP, and phe-tRNA. Although the phe-tRNA.EFTu.GMP.PNP complex containing the tufA gene product binds somewhat more tightly to ribosomes, both proteins promote the complete process of binding phe tRNA to ribosomes at similar rates.
Mol Gen Genet 1978 Feb 07
PMID:A comparison of the activities of the products of the two genes for elongation factor Tu. 34 85

A relA+ strain of E. coli with four amino acid requirements was starved separately for each amino acid, after which the levels of polysomes, guanosine-5'-diphosphate-3'-diphosphate and the residual net synthesis of RNA were determined. The polysome level and guanosine-5'-diphosphate-3'-diphosphate production were coordinately affected by starvation for the different amino acids, whereas no correlation was found between these two parameters and residual RNA synthesis. The main conclusion stemming from these results is that guanosine-5'-diphosphate-3'-diphosphate cannot act as the sole effector molecule in stringent control of RNA synthesis.
Mol Biol Rep 1978 Feb 28
PMID:The relationship between guanosine tetraphosphate, polysomes and RNA synthesis in amino acid starved Escherichia coli. 34 53

Treatment of elongation factor G (EF-G) with the thiol reagent N-ethylmaleimide only partially inhibits (10 to 70%) the activity of the factor in (a) guanosine nucleotide-EF-G-ribosome complex formation, (b) uncoupled ribosome-dependent GTP hydrolysis, and (c) polypeptide synthesis. Moreover, a similar treatment of the factor with N-[3H]ethylmaleimide does not lead to 3H-label being associated with a GDP-EF-G-ribosome-fusidic acid complex. Thus, the results indicate the presence in EF-G preparations of a form of the factor that does not react with N-ethylmaleimide.
Mol Biol Rep 1976 Apr
PMID:A form of elongation factor G insensitive to N-ethyl-maleimide. 77 17

The prostate glands of rats, mice, guinea pigs and hamsters were found to be a rich source of enzymes catalyzing the Mn2+-dependent transfer of galactose from UDP-galactose to glycoprotein acceptors such as ovomucoid and ovalbumin. The ventral prostate was also very active in promoting transfer of fucose from GDP-fucose to ovomucoid. The prostatic enzymes promoting both galactosyl and fucosyl transfers to glycoproteins were very largely membrane-bound, and were markedly activated by the non-ionic detergent Triton X-100. Castration of adult male resulted in a many-fold and roughly parallel decline in both glycosyltransferase activities over a period of two weeks, which was reversed by subsequent daily treatment with testosterone for 8 days. The very low galactosyltransferase of the ventral prostate of hypophysectomized rats was markedly enhanced by testosterone administration, whereas prolactin alone or in combination with androgen had no significant effect.
Mol Cell Endocrinol
PMID:Glycoprotein glycosyltransferases in male reproductive organs and their hormonal regulation. 82 97

GpppG was modified to m7 GpppGm by a cytoplasmic extract, prepared from embryonic lens cells, in a reaction mixture which contained S-adenosyl-methionine as methyl group donor. The appearance of m7 GpppGm was a function of time and lens extract concentration. S-adenosyl-homocysteine inhibited both the m7G and Gm modification reactions. Analogues of GpppG, pG, ppG and pppG were relatively ineffective as substrates.
Mol Biol Rep 1977 Jun
PMID:Detection of methyltransferase activities which modify Gppp G to m7GpppGm in embryonic chick lens. 88 98

The cell surface of embryonic chick liver cells contains transferases for mannose, fucose, galactose, N-acetyl-glucosamine and N-acetyl-neuraminic acid. Liver cells obtained by trypsin-dissociation of the tissue use the corresponding exogenous sugar nucleotides as substrates. The activities of the enzymes tested do not depend neither no the dissociation procedure nor on de novo protein synthesis. They vary considerably during development of the embryos, reaching maximal values at the 8th+/-1 day and at the 12th+/-1 day. Glycoproteins are the final stable endogenous acceptors for all sugars. Mannose transfer proceeds via a two or multistep reaction sequence. In a first step labile lipophilic intermediates are formed. Mannose can be liberated by treating the intermediates with 0.1 N HCl at 100 degrees C. In a second reaction step mannose becomes attached to glycoproteins. From embryonic chick liver cells a glycopeptide fraction has been obtained by pronase digestion followed by several purification steps. The purified glycopeptides inhibit all transferase systems and act as exogenous acceptors for mannose transfered from exogenous GDP-mannose.
Mol Cell Biochem 1976 Feb 16
PMID:Cell surface glycosyl transferase activities in liver cells of developing chicken embryos. 94 93

Trypsin dissociated intact cells of embryonic chick liver catalyze the transfer of mannose from exogenous GDP-mannose to glycoprotein in vitro. In cells of 8 day old embryos a surface bound mannosyltransferase-system forms several mannose containing isoprenoid-lipids in a primary step. One of these compounds serves as a substrate in the highly specific second step of the overall reaction, the transfer of mannose to glycoprotein. The isoprenoic intermediate has been isolated and its effectivity as substrate for the incorporation of mannose into glycoprotein has been examined.
Mol Cell Biochem 1976 Jun 15
PMID:Cell surface mannosyl transferase activity in the liver of embryonic chick. A mannose containing glycolipid as intermediate in glycoprotein synthesis. 94 63


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