Developmental alterations in 5′-nucleotidase kinetics and lipid composition of rat heart sarcolemma

The objective of these studies was to examine the mechanism by which the specific activity of heart sarcolemma 5′-nucleotidase decreases as function of age. We examined the kinetic properties and the lipid composition of the sarcolemma from animals with different ages. The age groups used were 1 month, 6-8 months and 13-15 months. It was found that the K_m of this enzyme increases as the animal develops from 1 month to 6-15 months. The opposite was true with 5′-nucleotidase V_max. There was no significant difference between the middle age and the older age groups in those parameters. The results of these experiments suggest that the increase in K_m in sarcolemma 5′-nucleotidase could be due to the reduction of the sarcolemmal polyunsaturated fatty acid concentration, the only lipid alteration observed.