Age dependent variations in choline and ethanolamine phosphorylating activities of rodents

The substrate concentration-velocity relationship as influenced by age of animal was determined. At all stages of growth of rat and mouse ethanolamine kinase activity responded with a hyperbolic pattern to substrate concentration. Choline kinase on the other hand, underwent "enzyme differentiation". In rat liver up to 4 days of age of animal, in mouse liver up to 7 days and in mouse kidney up to 15 days, choline kinase activity responded with a hyperbolic pattern; but from then onwards the response to substrate concentration was sigmoid. The results obtained pointed to the regulatory nature of choline kinase and a possible distinction between the proteins catalyzing the phosphorylation of the two bases.