The Effect of Reticulocytosis in the Rabbit on the Activities of Enzymes in Pyrimidine Biosynthesis

Five sequential enzymes leading to the formation of uridine-5'-phosphate were studied in acetophenylhydrazine-induced reticulocytes in the rabbit. All of these enzymes—aspartate carbamyltransferase, dihydroorotase, dihydroorotic dehydrogenase, orotidylic pyrophosphorylase, and orotidylic decarboxylase—decreased markedly in activity during in vivo maturation and aging of the reticulocytes. In analogy to previous studies on purine nucleotide biosynthesis, it is concluded that the reticulocyte, but not the mature erythrocyte, is capable of de novo pyrimidine nucleotide biosynthesis.