Kinetics and Compartmentation of Erythrocyte Pyrimidine Metabolism

Abstract

Purine metabolism and transport have been extensively studied in the mammalian erythrocyte; much less, however, is known about corresponding aspects of the metabolism of pyrimidines and their derivatives, or even whether pyrimidine nucleotides have any physiological role in the erythrocyte. Until quite recently it was considered, from studies on stored blood, that negligible metabolism of pyrimidine nucleotides took place in the erythrocyte¹. However, if fresh red cells are used it can be shown that both orotate and uridine can be actively taken up and converted to uridine nucleotides; the rate of nucleotide formation from uridine circulating in the plasma has been estimated to be about 0.8 nmol e/min 10¹⁰ RBC ². The rate of uridine nucleotide degradation back to uridine by the pyrimidine-specific 5’ nucleotidase of erythrocytes is of a comparable order, if the properties of this enzyme in cell-free preparations ^3,4 apply in the intact cell. Our previous studies on red cell uridine nucleotide degradation after pulse labelling normal and pyrimidine 5’ nucleotidase deficient red cells with (³H) uridine, confirm that rapid conversion to uridine occurs².