Pyrimidine catabolism in nocardia corallina : a thesis presented in partial fulflment for the degree of Master of Science in Biochemistry at Massey University

Abstract

The degradation of pyrimidines in living systems may be initiated by either a reductive step leading to the formation of a dihydropyrimidine intermediate, or an oxidative step yielding the corresponding barbituric acid. In the case of thymine however, the oxidative step can lead alternatively to the formation of 5-hydroxymethyluracil. In the following discussion of the literature oxidative catabolism is treated separately from reductive catabolism. 1. Oxidative catabolism of pyrimidines. A. Barbituric acids as intermediates. Studies by Lara (l952a), based in the principle of sequential induction, indicated that uracil and barbituric acid could be intermediates in the catabolism of thymine in N. corallina. From the observation that organisms induced for thymine oxidation were simultaneously induced for uracil Oxidation whereas organisms not induced for thymine catabolism did not attack uracil, Lara suggested that uracil was a possible intermediate in the breakdown of thymine. Further, since barbituric acid was oxidised more rapidly by thymine grown organisms, than those grown on yeast extract, it was proposed as the intermediate to follow uracil in the thymine catabolic sequence. [From Introduction]