Pyrimidine nucleoside phosphorylase during development of the normal and dystrophic chicken

Abstract

1. 1. The distribution of pyrimidine nucleoside phosphorylase was investigated in tissue extracts of young adult (3–5-month-old) chickens. Liver contained thymidine phosphorylase (deoxythymidine : orthophosphate deoxyribosyl transferase, EC 2.4.2.2) activity and kidney contained both thymidine and uridine phosphorylase (uridine : orthophosphate ribosyl transferase, EC 2.4.2.3) activity. Spleen, bone marrow, pancreas, heart and skeletal muscle did not contain measureable amounts of either enzyme. 2. 2. Liver thymidine phosphorylase increased markedly during development (18–19-day-old embryos to 3–5-month-old chickens) with the most dramatic increase occurring between the embryonic stage and the second week after hatching. Kidney thymidine and uridine phosphorylase activities showed slight or no change during the development period investigated (1-week-old to 3–5-month-old chickens). 3. 3. In liver extracts from dystrophic chickens, thymidine phosphorylase activity was less than that of comparable controls over the entire development period investigated. The difference was evident whether activity was determined in the direction of thymidine cleavage or in the direction of thymidine synthesis by either the phosphorolytic or deoxyribosyl transferase mechanisms. Pyrimidine nucleoside phosphorylase activities in kidney extracts from dystrophic chickens did not show any marked or consistant differences from comparable control values. 4. 4. The characteristics of thymidine phosphorylase activity in liver extracts from control and dystrophic chickens (3–5 months) did not differ with respect to pH optimum, phosphate dependence of thymidine cleavage, and K m value. There was no evidence for either dialyzable or non-dialyzable inhibitors or activators in either control or dystrophic liver extracts.