Enzymes of uracil metabolism in tissues with different growth characteristics

Abstract

Different tissues were investigated for their contents of uridine phosphorylase, uridine kinase, deoxyuridine phosphorylase and deoxyuridine kinase activities. These enzyme contents were considered to mirror the relative efficiency of an enzymic pathway using uracil for the biosynthesis of nucleic acid pyrimidines. Furthermore, the same tissues were investigated for their capacities to convert orotic acid to UMP, representing the de novo pathway of pyrimidine synthesis. In a survey of some normal tissues from rat, mouse and rabbit, a certain degree of correlation was found between the efficiency of this alternative pathway and the growth rate. During liver regeneration, marked increases in the enzymes studied were observed. Thus, uridine phosphorylase showed a maximal threefold increase between 36 and 72 h after hepactomy. Corresponding values were a fivefold increase for uridine kinase (24–36 h), a fourfold increase for deoxyuridine phosphorylase (about 48h), a tenfold increase for deoxyuridine kinase (36–48 h) and, for the enzymes transforming orotic acid to UMP a 5- tp 6-fold increase (about 48 h). 144 h after the operation, all enzymes had reverted to almost normal values. These rapid changes in the activities of enzymes involved in the synthesis of nucleotides, might form part of an homeostatic mechanism involved in pyrimidine biosynthesis.