Orotidine 5 -phosphate pyrophosphorylase

OROTIDYLATE DECARBOXYLASE Orotidine-5 -phosphate decarboxylase, OROTIDYLATE DECARBOXYLASE Orotidine-5 -phosphate pyrophosphorylase,... 

Pyrimidine synthesis Aspartate carbamoyltransferase Orotidine-5-phosphate pyrophosphorylase... 

P14 Pausch, J., Keppler, D. and Decker, K. Increased activities of hepatic orotidine 5 -phosphate pyrophosphorylase and orotidine 5 -phosphate decarboxylase induced by orotate. FEBS Lett. 20, 330-332 (1972)... 

The formation of the first nucleotide in the pyrimidine sequence, orotidylic acid (orotidine 5 -phosphate), was accomplished by the reaction of 5-phosphoribosyl-l-pyrophosphate (PRPP) with orotic acid 83) (Fig. 22). Other pyrimidines and carbamylaspartic acid did not react with PRPP in the presence of the enzyme, which has been named orotidine 5 -phosphate pyrophosphorylase. Several purine analogs, e.g., 6-uracilsulfonic acid, 6-uracil methyl sulfone, which inhibited the growth of several organisms (S78, 379), probably inhibited the formation of orotidylic acid. 

A specific uridine 5 -phosphate pyrophosphorylase has been purified from bacterial extracts (48, 60). The enzyme was found in a strain of lactic acid bacteria which could utilize uracil for growth, but was not found in one which required orotic acid. The latter strain contained only orotidine 5 -phosphate pyrophosphorylase. Some strains contain both enzymes (60). 

The carbamyl phosphate is condensed with a molecule of aspartate giving ureidosuccinic acid, from which orotic acid is formed by cyclization and oxidation. In the presence of PRPP and a pyrophosphorylase this acid forms a ribotide and decarboxylation yields uridine monophosphate. The decarboxylation of the product of amination of orotidine phosphate gives cytidine monophosphate (Fig. 75). It can be seen that the pentose intermediate in pyrimidine nucleotide biosynthesis is PRPP, the same as for purine nucleotide biosynthesis. 

Orotidine S -monophosphate, OMPi a nucleotide of orotic acid. M, 368.2. OMP is an intermediate in Pyrimidine biosynthesis (see). Orotidine 5 -phos-phate pyrophosphorylase catalyses the synthesis of OMP from orotic add and S-phosphoribosyl 1-pyro-phosphate. 

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