Catabolism of Pyrimidines in Rape Seedlings

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Abstract
Externally-added thymine and uracil were cata-bolized by rape seedlings through the 5,6-dihydropyrimidines and [beta]-ureidoamino acids to give [beta]-aminoisobutyric acid and [beta]-alanine, respectively. Uracil-5,6-H3 and [beta]-alanine-2-C14 gave rise to labelled carboxylic acids, including malic, pyruvic and citric acids. [beta]-Alanine was also incorporated into lipids and sterols. Results of comparative studies with [beta]-alanine-1-C14 were explicable on the basis of the con- version of [beta]-alanine to acetate by a mechanism involving loss of its carboxyl C. The possibility that the degradation of [beta]-alanine proceeds through formylacetic acid was supported by the demonstration of a [beta]-alanine-L-glutamic acid transaminase in the rape seedlings. This is apparently the 1st report of a [beta]-alanine transaminase in higher plants. No degradation products were detected when cytosine was furnished to the seedlings. Cytidine deaminase was demonstrated in the seedlings, but cystosine deaminase was not detected. No cytidine deaminase was found in the ungerminated seed.