Uridine 5 - , enzymic

Sugar nucleotides are formed from sugar-l-phosphates and nucleoside triphosphates by specific pyrophosphorylase enzymes (Figure 23.18). For example, UDP-glucose pyrophosphorylase catalyzes the formation of UDP-glucose from glucose-l-phosphate and uridine 5 -triphosphate ... 

While mammahan cells reutilize few free pyrimidines, salvage reactions convert the ribonucleosides uridine and cytidine and the deoxyribonucleosides thymidine and deoxycytidine to their respective nucleotides. ATP-dependent phosphoryltransferases (kinases) catalyze the phosphorylation of the nucleoside diphosphates 2 "-de-oxycytidine, 2 -deoxyguanosine, and 2 -deoxyadenosine to their corresponding nucleoside triphosphates. In addition, orotate phosphoribosyltransferase (reaction 5, Figure 34-7), an enzyme of pyrimidine nucleotide synthesis, salvages orotic acid by converting it to orotidine monophosphate (OMP). 

Figure 36-4. Illustration of the tight correlation between the presence of RNA polymerase II and RNA synthesis. A number of genes are activated when Chirono-mus tentans larvae are subjected to heat shock (39 °C for 30 minutes). A Distribution of RNA polymerase II (also called type B) in isolated chromosome IV from the salivary gland (at arrows). The enzyme was detected by immunofluorescence using an antibody directed against the polymerase. The 5C and BR3 are specific bands of chromosome IV, and the arrows indicate puffs. B Autoradiogram of a chromosome IV that was incubated in H-uridine to label the RNA. Note the correspondence of the immunofluorescence and presence of the radioactive RNA (black dots). Bar = 7 pm. (Reproduced, with permission, from Sass H RNA polymerase B in polytene chromosomes. Cell 1982 28 274. Copyright 1982 by the Massachusetts Institute of Technology.)...

Patient and tumor biology also affect how cancer therapy is dosed. Patients with a uridine diphosphate-glucuronosyltransferease 1A1 enzyme deficiency can have... 

The increase in erythrocyte destruction may be due in part to inhibition by lead of pyrimidine-5 -nucleotidase, which results in an accumulation of pyrimidine nucleotides (cytidine and uridine phosphates) in the erythrocyte or reticulocyte. This enzyme inhibition and nucleotide accumulation affect erythrocyte membrane stability and survival by alteration of cellular energetic (Angle et al. 1982 EPA 1986a). Formation of the heme-containing cytochromes is inhibited in animals treated intraperitoneally or orally... 

D-Galaktose entsteht nach L. F. Leloir in der Natur aus D-Glucose durch enzymatische Konfigurationsumkehr des C-4 auf der Stufe der a-1-Phosphate. Die Enzyme, die diese Inversion vollbringen, benotigen als Cofaktor Uridin-diphosphat-glucose (UDPG). Nun konnte. aus... 

Synthesis of sucrose 6 -phosphate by an enzymic method using uridine 5 -(a-D-glucopyranosyl diphosphate) plus D-glucose 6-phosphate has been reported.126-131 The first, unambiguous, chemical synthesis of sucrose 6 -phosphate was achieved by Buchanan and coworkers.18 The reaction of 2,3,4,6,l, 3, 4 -hepta-0-acetylsucrose, prepared by five steps of synthesis, with cyanoethyl phosphate in pyridine gave a crude product from which sucrose 6 -phosphate was isolated as the barium salt. 

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. 

Phenobarbital, phenytoin, primidone, and carbamazepine are potent inducers of cytochrome P450 (CYP450), epoxide hydrolase, and uridine diphosphate glucuronosyltransferase enzyme systems. Valproic acid inhibits many hepatic enzyme systems and displaces some drugs from plasma albumin. 

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