Thymidine kinase and thymidylate kinase in the silkworm, Antheraea pernyi

Abstract

1. Thymidine kinase (ATP: thymidine-5′-phosphotransferase, EC 2.7.1.21) and thymidylate kinase were extracted from the wing epidermis of developing adults of Antheraea pernyi and partially characterized. 2. Activity of both enzymes was low in dialysed extracts unless Mg 2+ was added. Non-dialysed extracts contained sufficient Mg 2+ for the full activation of thymidine kinase but not for full activation of thymidylate kinase. 3. High concentrations of Mg 2+ or of ATP inhibited thymidine kinase but this inhibition disappeared when both cofactors were added in equimolar concentrations. High concentrations of thymidine also inhibited thymidine kinase; this inhibition was diminished by lowering the concentration of ATP. 4. Thymidine kinase was inhibited about 45 % when thymidine and deTTP were equimolar. deCTP also inhibited thymidine kinase but to a lesser degree; i.e. by about 50 % when the deCTP concentration was 10 times that of thymidine. deGTP and deATP caused to detectable inhibition. However, to a certain extent, these factors were able to satisfy the requirements for ATP.