Ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) has been purified from 3T3- and SV40-transformed 3T3 mouse fibroblasts by affinity chromatography, and the physicochemical properties of the two enzymes compared. Measured properties include molecular weight of the active species, subunit molecular weight and specific activity of the purified enzymes, kinetic parameters, thermostability, degradation rate in vivo and immunological cross-reactivity. Although crude extracts of the transformant possess more ornithine decarboxylase activity per mg of protein than the parent strain, there is no evidence for the appearance of an altered form of the enzyme in these cells. The results reported in the present paper indicate that the increased ornithine decarboxylase activity in the transformed cells is the result of higher enzyme biosynthesis de novo.
