Uridine-5 -phosphate hydrolysis

As shown in Sec. I, uracils have represented, for more than 90 years, a class of compounds that continually attract organic chemists, biochemists, medicinal chemists, and photobiologists. Uracils were first detected as constituents of ribonucleic acids, from which they were prepared by hydrolysis. Nucleosides derived from uracil are called uridine, pseudouridine, and uridine phosphate, respectively. Recently, uracil moieties were detected in the antibiotic Tunicamycin (85JA7761). 

A uridine phosphate (5), obtained by treatment of uridine 5 -(a-D-glucopyranosyl pyrophosphate) with ammonia, imdergoes hydrazinolysis to D-ribose 5-phosphate (2) and 3-pyrazolone, which establishes the structure of (S) as uridine 5 -phosphate. - (Hydrazinolysis of uridine to pyrazolone, with the liberation of the sugar moiety, had been described, and has served as a useful tool in the determination of the position of attachment of the sugar moiety to the aglycon. ) The 5 -phosphates of adenosine, guanosine, cytidine, and uridine were obtained by enzymic hydrolysis of ribonucleic acid with phosphodiesterases from snake venom and from other sources (such as Streptomyces aureu ). 

Alkaline hydrolysis splits the nucleotide into its phosphate and sugar-base residues. The sugar-base is known as a nucleoside. The nucleosides are named according to the type of base present. If a purine base is present it will end -osine, e.g. adenosine, while if a pyrimidine is present the name will end -idine, e.g. uridine. 

Mild, acidic hydrolysis of the derivative 41 gave uridine 5 -pyrophosphate, 2-acetamido-2-deoxy-D-glucose 6-phosphate, and D-galactose. Alkaline degradation leads to uridine 5 -(2-acetamido-2-deoxy-a-D-glucopyranosyl pyrophosphate) and a-D-galactopyranosyl phosphate, among other products. 

Alkaline hydrolysis of uridine 5 - (a - D- glucopyranosyl pyrophosphate) results in the formation of uridine 5 -phosphate and a-D-glu-copyranose 1,2-cyclic phosphate24 (81). The reaction reaches completion after 30 min at 0° in concentrated aqueous ammonia, or after 2 min at 100° and pH 8.5. Partial conversion of the cyclic phosphate (81) into a-D-glucopyranosyl phosphate and D-glucose 2-phosphate occurs under conditions of elevated temperature. 

Hydrolysis of sugar nucleotides with unspecific pyrophosphatases has already been mentioned (Section 11,1, p. 310). A similar reaction is catalyzed by a bacterial enzyme specific for adenosine 5 -(a-D-glucopyranosyl pyrophosphate).459 The specific conversion of uridine 5 -(a-D-glucopyranosyl pyrophosphate) into a-D-glucopyranosyl phosphate, uridine, and inorganic phosphate was observed with an enzyme from Escherichia colt 459,460 a preparation from Bacillus subtilis can act in a similar manner461 on different sugar nucleotides. ... 

Ribonuclease Ua digestion of ApU has revealed reduced hydrolase activity in the second step of RNase U2 action (30). When 87.4% of ApU was readily degraded to produce uridine and adenosine 2, 3 -cyclic phosphate, no 3 -adenylic acid was detected. After exhaustive degradation of ApU, hydrolysis of adenosine 2, 3 -cyclic phosphate occurred and 3 -adenylic acid gradually appeared. 

A good source of uncommon bases is tRNA. It provides substrates for studying the effect of base on the rate of hydrolysis. Baev et al. (62) showed that V2-dimethylguanylyl-(3 -5 )-cytidine-3 phosphate (G2m-pCp) was hydrolyzed much slower than the usual GpCp. Venkstern (63) reported that Tp was hydrolyzed very slowly. Naylor et al. (64) found that Cp was hydrolyzed with half the rate of CpU. The same group of workers introduced (64, 65) a chemical block on uridine and pseudo-uridine residues by reacting RNA with l-cyclohexyl-3-(2-morpho-liny]-(4)-ethyl)-carbodiimide metho-p-toluene sulfonate. The modification of the uridine residues completely blocked the action of venom exonuclease and also blocked the action of pancreatic RNase. 

The sugar configuration about the T, 2, 3, and 4 positions can be changed by synthesis. A variety of pyrimidine nucleoside cyclic phosphates have been made. Ukita et al. (425) prepared -D-lyxo-uridine 2 3 -cyclic phosphate (Fig. 21a). The configuration about the 2 and 3 positions is inverted and the two OH groups are now cis to the base rather than trans as in the D-ribose series. No hydrolysis at all of this compound was observed in the presence of RNase. However, both the cyclic phosphate and the free 2 (3 )-nucleotides inhibit the enzyme. The... 

Wladkowski, B.D., L.A. Svensson, L. Sjolin, J.E. Ladner, and G.L. Gilliland. 1998. Structure (1.3 A) and charge state of a ribonuclease A-uridine vanadate complex Implications for the phosphate ester hydrolysis mechanism. J. Am. Chem. Soc. 120 5488-5498. 

The glucose 1-phosphate is then activated to enable its incorporation into glycogen. This activation involves the expenditure of energy derived from the hydrolysis of a molecule of uridine triphosphate (UTP) by UDP-glucose pyrophosphorylase. 

One is from glucose 1-phosphate and the other is from uridine monophosphate (UMP). The pyrophosphate that is liberated from the terminal phosphates of UTP is hydrolyzed to inorganic phosphate by the enzyme pyrophosphatase. This hydrolysis, which is irreversible, drives the reaction in the direction of UDP-glucose synthesis. 

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