Catabolism of Pyrimidines in Rape Seedlings

Thymine-2-C14 and uracil-2-C14 were previously shown by Evans and Axelrod (5) to be reductively catabolized by germinating rape seed to the corresponding dihydropyrimidines, dihydrothymine and dihydrouracil, which were in turn hydrolyzed to give ,8-ureidoisobutyric acid and fi-ureidopropionic acid (BUP) respectively. By analogy with the reactions observed in animal tissues and microorganisms (3,4, 8, 9, 12) it was to be expected that corresponding ,3amino acids, ,8-aminoisobutyric acid (BAIB) and ,8-alanine would be formed. They were not detected in the above experiments with rape seedlings because the labelled C was lost as CO2 following decarbamylation. Subsequently it was shown in this laboratory by the use of thymine-H3, that in Iris BAIB originated from thymine (6). The objectives of the experiments described here were to extend the observations with the rape seedlings using suitable labelled pyrimidines, to confirm the existence of the indicated catabolic pathways and to investigate the subsequent metabolism of /8-alanine in the seedlings. While the present work was underway, Barnes and Naylor demonstrated that 6-alanine arose from uracil in pine tissues (2).