Pyrimidine metabolism in peripheral and phytohemagglutinin-stimulated mammalian lymphocytes.

1. Activity of uridine kinase was very low in ovine lymphocytes and in those of some pigs. Lymphocytes of other pigs showed a significantly higher activity of this enzyme. Activity of uridine kinase in lymphocytes of man, horse and cattle was intermediate. 2. Activity of uridine phosphorylase was higher than that of uridine kinase with lymphocytes of all species. 3. Activity of uridine kinase in equine lymphocytes increases at PHA-stimulation and also in porcine lymphocytes with a low activity at the start of the culture. Activity of uridine kinase decreased in porcine lymphocytes with a high activity at the start of the culture. 4. Activity of uridine phosphorylase increases at PHA-stimulation with equine and porcine lymphocytes and during culturing of non-stimulated porcine lymphocytes. 5. Activities of OPRT and ODC decrease in cultures of porcine lymphocytes with and without PHA. 6. Activity of OPRT in lysates of porcine lymphocytes is inhibited by purine nucleosides and by guanine and pyrimidine nucleotides.