Properties of Uridine and Thymidine Phosphorylating Enzymes of Zea Mays

Abstract

The studies support the previous conclusion that 2 uridine phosphorylating enzymes exist during germination of Z. mays, of which only one is active in vitro during the initial 48 hr of germination. The earlier enzyme is less heat stable and of higher molecular weight than the later one, which becomes active after this time. The evidence presented indicates that the 2nd enzyme is identical with thymidine kinase. It consists of 2 components of equal molecular size, each of which is slightly smaller than bovine serum albumin. Both are inactivated at temperatures above 55''C but component T is somewhat more stable than component P. The latter is already present in small amounts during early germination stages. Competitive inhibition of thymidine phosphorylation by uridine and of uridine phosphorylation by thymidine occurred, the Km''s for thymidine and uridine being equal to the respective Kj''s with similar turn-over numbers for both reactions.