Analysis of purine nucleoside phosphorylase from human T and non-T lymphocytes of different maturation stages.

In the last few years evidence has been growing that purine/pyrimidine metabolism changes during maturation of lymphocytes. In this view enzyme characteristics of lymphocytes may act as biochemical markers of lymphocyte maturation. Human purine nucleoside phosphorylase (PNP) has been studied in extracts of T lymphocytes isolated from thymic tissue, cord blood, and peripheral blood, as well as in extracts of non-T lymphocytes from cord blood, peripheral blood and tonsils. Using inosine or deoxyinosine as a substrate, complicated kinetics of PNP are observed which may be caused by the presence of multiple active enzyme species. The number of PNP-active molecular forms increases with the maturation stage of the T and B lymphocytes as shown by cellogel electrophoresis. PNP activity of thymocytes as compared to peripheral blood T cells is low; PNP activity of peripheral blood B cells as compared to neonatal B cells does not differ significantly. The difference found in PNP activity between thymocytes and peripheral blood T cells is caused by the difference in amount of PNP protein, as has been demonstrated by immunoprecipitation tests.