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At least 19 recordsLinked to original sources
PubMed1991

Synthesis of the coenzymes adenosine diphosphate glucose, guanosine diphosphate glucose, and cytidine diphosphoethanolamine under primitive Earth conditions.

The nonenzymatic synthesis of the coenzymes adenosine diphosphate glucose (ADPG), guanosine diphosphate glucose (GDPG), and cytidine diphosphoethanolamine (CDP-ethanolamine) has been carried out under conditions considered to have been prevalent on the early Earth. The production of these compounds was performed by allowing simple precursor molecules to react under aqueous solutions, at moderate temperatures and short periods of time, with mediation by cyanamide or urea. These two condensing agents are considered to have been present in significant amounts on the primitive Earth and have been previously used in the nonenzymatic synthesis of several other important biochemical compounds. In our experiments, ADPG was obtained by heating glucose-1-phosphate (G1P) and ATP in the presence of cyanamide for 24 h at 70 degrees C. The reaction of G1P and GTP under the same conditions yielded GDPG. The cyanamide-mediated production of CDP-ethanolamine was carried out by reacting a mixture of ethanolamine phosphate and CTP for 24 h at 70 degrees C. The separation and identification of the reaction products was carried out by paper chromatography, thin-layer chromatography, high performance thin-layer chromatography, high performance liquid chromatography, both normal and reverse-phase, UV spectroscopy, enzymatic assays, and acid hydrolysis. Due to the mild conditions employed, and to the relative ease of these reactions, these studies offer a simple attractive system for the nonenzymatic synthesis of phosphorylated high-energy metabolic intermediates under conditions considered to have been prevalent on the ancient Earth.

Adenosine Diphosphate Glucose↗
PubMed1992

Kinetic analysis of the activation of transducin by photoexcited rhodopsin. Influence of the lateral diffusion of transducin and competition of guanosine diphosphate and guanosine triphosphate for the nucleotide site.

The activation of transducin (T) by photoexcited rhodopsin (R*) is kinetically dissected within the framework of Michaelis-Menten enzymology, taking transducin as substrate of the enzyme R*. The light scattering "release" signal (Vuong, T.M., M. Chabre, and L. Stryer, 1984, Nature (Lond.). 311:659-661) was used to monitor the kinetics of transducin activation at 20 degrees C. In addition, the influence of nonuniform distributions of R* on these activation kinetics is also explored. Sinusoidal patterns of R* were created with interference fringes from two crossed laser beams. Two characteristic times were extracted from the Michaelis-Menten analysis: t(form), the diffusion-related time needed to form the enzyme-substrate R*-transducin is 0.25 +/- 0.1 ms, and T(cat), the time taken by R* to perform the chemistry of catalysis on transducin is 1.2 +/- 0.2 ms, in the absence of added guanosine diphosphate (GDP) and at saturating levels of guanosine triphosphate (GTP). With t(form) being but 20% of the total activation time t(form) + t(cat), transducin activation by R* is not limited by lateral diffusion. This is further borne out by the observation that uniform and sinusoidal patterns of R* elicited release signals of indistinguishable kinetics. When (GDP) = (GTP) = 500 microM, t(cat) is lengthened twofold. As the in vivo GDP and GTP levels are comparable, the exchange of nucleotides may well be the rate-limiting process.

Animals↗
PubMed1975

Interaction of guanosine nucleotides with elongation factor 2. II. Effect of ribosomes and magnesium ions on guanosine diphosphate and guanosine triphosphate binding to the enzyme.

The effects of ribosomes and Mg-2plus on the binding of GDP and GTP to elongation factor 2 (EF-2) have been studied by an improved filter-binding assay. Both ribosomes and Mg-2plus strongly inhibit the binding of GDP but have apparently no effect on the GTP binding to the enzyme. An apparent stimulation by ribosomes of GTP binding to EF-2 is time-dependent and parallels a concomitant increase of the GDP concentration in the incubation mixture. Based on these results and evidence obtained by other investigators it is suggested that changes in the GTP:GDP ratio associated with the elongation and termination reactions of protein synthesis cause conformational changes of the respective factors which consequently will modulate the binding and dissociation of the enzymes from ribosomes. Further evidence of the role GDP may play as a modulator of protein synthesis might possibly be provided by studies of the GTP-GDP transphosphorylase activity which is present as an impurity in highly purified preparations of EF-2 as well as in ribosome preparations. It is demonstrated that relatively high concentrations of GDP in the presence of GTP completely block the ribosome-dependent GTPase activity of EF-2. Instead, the transphosphorylase enzyme(s) catalyzes an exchange reaction between GTP and GDP during which GDP remains bound to EF-2 and the relative concentrations of the two nucleotides do not change.

Animals↗
PubMed1971

Rate studies of polysaccharide biosynthesis from guanosine diphosphate -D-glucose and guanosine diphosphate -D-mannose.

With enzyme preparations from Phaseolus aureus seedlings, the initial rate of (14)C-labelled polysaccharide formation from GDP-alpha-d-[(14)C]glucose is not increased by additions of GDP-alpha-d-mannose. However, final incorporation is increased by addition of GDP-alpha-d-mannose, since the total reaction-time is extended. In contrast, the initial rate of (14)C-labelled polysaccharide formation from GDP-alpha-d-[(14)C]mannose is increased by all concentrations of GDP-alpha-d-glucose that are less than that of the GDP-alpha-d-[(14)C]mannose. Maximum stimulation of the initial rate occurs at a GDP-alpha-d-[(14)C]mannose/GDP-alpha-d-glucose concentration ratio of about 4:1. However, eventual incorporation from GDP-alpha-d-[(14)C]mannose is decreased by the addition of GDP-alpha-d-glucose, since the reaction rate falls off sharply after about 2min. Reciprocal plots of (14)C-labelled polysaccharide formation from GDP-alpha-d-[(14)C]mannose result in biphasic graphs. The two straight-line portions of the plot are joined by a curved line in the concentration range between 2-3 and 50mum. Extrapolated K(m) values for the two linear components are 0.4-1.0 and 700-1500mum. The effect of GDP-alpha-d-glucose on the kinetics of (14)C-labelled polysaccharide formation from GDP-alpha-d-[(14)C]mannose is complex, and depends on relative concentrations of the two sugar nucleotides. (14)C-labelled polysaccharide formation from GDP-alpha-d-[(14)C]glucose also results in biphasic reciprocal plots. One component appears to have K(m) about 2-3mum, the other about 200-400mum. In this reaction, GDP-alpha-d-mannose appears to be a competitive inhibitor with K(i) 20-30mum. With particulate preparations of P. aureus, GDP-alpha-d-[(14)C]glucose appears to be a precursor for the synthesis of one polysaccharide, a glucomannan, the mannose moieties of which are derived from an intermediate existing in the particulate preparation. From the rate results, GDP-alpha-d-[(14)C]mannose appears to be a precursor for at least two polysaccharides, one of which is a glucomannan.

Carbon Isotopes↗
PubMed1976

Formation of uridine diphosphate 2-deoxy-D-glucose and guanosine diphosphate 2-deoxy-D-glucose in vitro using animal enzymes.

The enzymic formation of guanosine diphosphate 2-deoxy-D-glucose and uridine diphosphate 2-deoxy-D-glucose from synthetically prepared 2-deoxy-D-glucose 1-phosphate is described. Incubation of 2-deoxy-D-glucose 1-phosphate with an enzyme preparation from bovine mammary glands and either GTP or UTP gives rise to the corresponding nucleoside-diphosphate derivative of 2-deoxy-D-glucose. Uridine diphosphate 2-deoxy-D-glucose could also be obtained by incubation of 2-deoxy-D-glucose 1-phosphate with UTP and UDP glucose pyrophosphorylase from beef liver.

Animals↗
PubMed1968

Trehalose phosphate synthesis in Streptomyces hygroscopicus: purification of guanosine diphosphate D-glucose: D-glucose-6-phosphate 1-glucosyl-transferase.

Guanosine diphosphate d-glucose:d-glucose-6-phosphate 1-glucosyl-transferase was purified approximately 100-fold from extracts of Streptomyces hygroscopicus. The purified enzyme catalyzed the transfer of glucose from guanosine diphosphate-d-glucose to glucose-6-phosphate to form trehalose phosphate and guanosine diphosphate. The enzyme was specific for these two substrates and was stimulated by the addition of magnesium ions. The product was characterized as alpha-alpha-trehalose-6-phosphate by its physical and chemical properties. The enzyme was present in a large number of Streptomyces species, suggesting that this group of organisms synthesized trehalose phosphate in a unique manner. This enzyme was not detected in fungi, since these organisms utilized uridine diphosphate-d-glucose as the glucosyl donor.

Carbon Isotopes↗
PubMed1989

Specificity of GDP-Man:dolichyl-phosphate mannosyltransferase for the guanosine diphosphate esters of mannose analogues containing deoxy and deoxyfluoro substituents.

Guanosine diphosphate (GDP) esters of 2-deoxy-D-glucose (2dGlc), 2-deoxy-2-fluoro-D-mannose (2FMan), 3-deoxy-D-mannose (3dMan), 4-deoxy-D-mannose (4dMan) and 6-deoxy-D-mannose (6dMan) have been synthesised and tested for their ability to act as inhibitors of dolichyl phosphate mannose synthesis (enzyme: GDP-mannose:dolichyl-phosphate mannosyltransferase, EC 2.4.1.83) in chick embryo cell microsomal membranes. The following order of efficiency was found with the apparent Ki in parentheses: GDP-6dMan (0.40 microM +/- 0.15) greater than GDP-3dMan (1.0 microM +/- 0.1) = GDP-2dGlc (1.3 microM +/- 0.2) greater than GDP-4dMan (3.1 microM +/- 0.1) GDP-2FMan (15 microM +/- 0). For comparison the Km for GDP-Man was 0.52 microM +/- 0.02 and the Ki for GDP was 56 microM +/- 2. These results indicate that the 6-hydroxyl group of mannose is not crucial for enzyme-substrate recognition, whereas the 2- and 3-hydroxyls may have some involvement. The 4-hydroxyl appears to be an important determinant for enzyme-substrate recognition in this mannosyltransferase.

Animals↗
PubMed1987

The role of C-4-substituted mannose analogues in protein glycosylation. Effect of the guanosine diphosphate esters of 4-deoxy-4-fluoro-D-mannose and 4-deoxy-D-mannose on lipid-linked oligosaccharide assembly.

The effects of the guanosine diphosphate esters of 4-deoxy-4-fluoro-D-mannose (GDP-4FMan) and 4-deoxy-D-mannose (GDP-4dMan) on reactions of the dolichol pathway in chick-embryo cell microsomal membranes were investigated by studies with chick-embryo cell microsomal membranes in vitro and in baby-hamster kidney (BHK) cells in vivo. Each nucleotide sugar analogue inhibited lipid-linked oligosaccharide biosynthesis in a concentration-dependent manner. GDP-4FMan blocked in vitro the addition of mannose to Dol-PP-(GlcNAc)2Man from GDP-Man (where Dol represents dolichol), but did not interfere with the formation of Dol-P-Man, Dol-P-Glc and Dol-PP-(GlcNAc)2. Although GDP-4FMan and Dol-P-4FMan were identified as metabolites of 4FMan in BHK cells labelled with [1-14C]4FMan, GDP-4FMan was a very poor substrate for GDP-Man:Dol-P mannosyltransferase and Dol-P-4FMan could only be synthesized in vitro if the chick-embryo cell membranes were primed with Dol-P. It therefore appears that the inhibition of lipid-linked oligosaccharide formation in BHK cells treated with 4FMan [Grier & Rasmussen (1984) J. Biol. Chem. 259, 1027-1030] is due primarily to a blockage in the formation of Dol-PP-(GlcNAc)2Man2 by GDP-4FMan. In contrast, GDP-4dMan was a substrate for those mannosyltransferases that catalyse the transfer of the first five mannose residues to Dol-PP-(GlcNAc)2. In addition, GDP-4dMan was a substrate for GDP-Man:Dol-P mannosyltransferase, which catalysed the formation of Dol-P-4dMan. As a consequence of this, the formation of Dol-P-Man, Dol-P-Glc and Dol-PP-(GlcNAc)2 may be inhibited through competition for Dol-P. In BHK cells treated with 10 mM-4dMan, Dol-PP-(GlcNAc)2Man9 was the major lipid-linked oligosaccharide detected. Nearly normal extents of protein glycosylation were observed, but very little processing to complex oligosaccharides occurred, and the high-mannose structures were smaller than in untreated cells.

Animals↗
PubMed1992

Ca2+ potentiates corticotropin-induced, but not isoproterenol-induced, [3H]guanosine diphosphate release in rat adipocyte membranes.

EGTA abolished corticotropin (ACTH)-stimulated adenylate cyclase in rat adipocyte membranes. In contrast, the potency of guanosine triphosphate (GTP) stimulation of adenylate cyclase activated with ACTH was greater in the presence of Ca2+ (1 mmol/L). EGTA (1 mmol/L) powerfully inhibited ACTH-stimulated [3H]guanosine diphosphate (GDP) release from membranes prelabeled with [3H]GTP in the presence of isoproterenol (ISO) or ACTH, whereas Ca2+ significantly increased it. In contrast, neither EGTA nor Ca2+ affected ISO-stimulated [3H]GDP release. These data clearly show that Ca2+ is necessary for the binding of ACTH to its receptor, and that Ca2+ stimulates the interaction of the ACTH-occupied receptor with GTP-binding proteins.

Adenylyl Cyclases↗