Nucleoside diphosphokinase

Enzymes a) citrate synthase b) aconitase c) isocitrate dehydrogenase d) a-oxoglutarate dehydrogenase e) succiny CoA synthetase f) succinate dehydrogenase g) fumarase h) malate dehydrogenase i) nucleoside diphosphokinase. 

UDP and UTP are selective agonists of certain of the P2Y receptors. It is not yet clear what factors control the release of uridine nucleotides into the extracellular space. UTP can be formed from UDP in the extracellular space by the action of the enzyme nucleoside diphosphokinase, which catalyzes the transfer of the -phosphate of nucleoside triphosphates to nucleoside diphosphates, e.g., ATP + UDP —> ADP + UTP. 

In the preceding sections the conversion of purines and purine nucleosides to purine nucleoside monophosphates has been discussed. The monophosphates of adenosine and guanosine must be converted to their di- and triphosphates for polymerization to RNA, for reduction to 2 -deoxyribonucleoside diphosphates, and for the many other reactions in which they take part. Adenosine triphosphate is produced by oxidative phosphorylation and by transfer of phosphate from 1,3-diphosphoglycerate and phosphopyruvate to adenosine diphosphate. A series of transphosphorylations distributes phosphate from adenosine triphosphate to all of the other nucleotides. Two classes of enzymes, termed nucleoside mono-phosphokinases and nucleoside diphosphokinases, catalyse the formation of the nucleoside di- and triphosphates by the transfer of the terminal phosphoryl group from adenosine triphosphate. Muscle adenylate kinase (myokinase)... 

Lam, S.C.T. Packham, M.A. Isolation and kinetic studies of nucleoside diphosphokinase from human platelets and effects of cAMP phosphodiesterase inhibitors. Biochem. Pharmacol., 35, 4449-4455 (1986)... 

Colomb, M.G. Cheruy, A. Vignais, P.V. Nucleoside diphosphokinase from beef heart cytosol. I. Physical and kinetic properties. Biochemistry, 11, 3370-3378 (1972)... 

Nakamura, H. Sugino, Y. Metabolism of deoxyribonucleotides. 3. Purification and some properties of nucleoside diphosphokinase of calf thymus. J. Biol. Chem., 241, 4917-4922 (1966)... 

Ratliff, R.L. Weaver, R.H. Lardy, H.A. Kuby, S.A. Nucleoside-triphosphate-nucleoside diphosphate transphosphorylase (nucleoside diphosphokinase). 1.Isolation of the crystalline enzyme from brewerseast. J. Biol. Chem., 239, 301-309 (1964)... 

Ingraham, J.L. Ginther, C.L. Nucleoside diphosphokinase from Salmonella typhimurium. Methods Enzymol., 51, 371-375 (1978)... 

Imidazole (histidine) Phosphoglycerate mutase, succinyl-CoA synthetase, nucleoside diphosphokinase, histone phosphokinase, acid phosphokinase Phosphorylenzyme... 

The phosphorylation of GDP in this reaction is an example of substrate-level phosphorylation, and this is the only reaction in the citric acid cycle to produce a high-energy phosphate bond directly. The energy for this phosphorylation is derived from the hydrolysis of the thioester bond of succinyl-CoA. Subsequently, GTP phosphorylates ADP, catalyzed by nucleoside diphosphokinase, but this reaction... 

Nucleoside diphosphokinase The flux expression for nucleoside diphosphokinase is... 

The GTP formed as described above yields ATP [via nucleoside diphosphokinase]. The reduced coenzymes (4 NADH and FADH2) feed electrons into the mitochondrial electron transport chain (ETC) to yield 14 ATP per pyruvate oxidized (12 ATP/4 NADH and 2 ATP/FADH2) through the process of oxidative phosphorylation as described in Section 13.5. This total yield of ATP corresponds to a total of 32 ATP per glucose oxidized plus a further 6 ATP from mitochondrial oxidation of NADH generated in glycolysis, that is, 38 ATP per glucose oxidized. 

We have already seen that GTP is an important component of signal-transduction systems (Chapter 15). Alternatively, its y-phosphoryl group can be readily transferred to ADP to form ATP, in a reaction catalyzed by nucleoside diphosphokinase. 

What is the cost of converting glucose 6-phosphate into glycogen and back into glucose 6-phosphate The pertinent reactions have already been described, except for reaction 5, which is the regeneration of UTP. ATP phosphorylates UDP in a reaction catalyzed by nucleoside diphosphokinase. 

UDP is a nucleotide intermediate in pyrimidine biosynthesis. It is produced from UMP by UMP kinase, as shown in Figure 22.10 and is converted to UTP by nucleoside diphosphokinase (also in Figure 22.10). 

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