Changes in the Kinetic Properties of Renal Arachidonoyl-CoA Synthetase during Development in the Rat

Abstract

Changes in endogenous levels of phospholipid arachidonic acid and in its radioactive incorporation can be detected in the rat kidney medulla during maturation. In an effort to explain this phenomenon, the arachidonoyl-CoA synthetase activity in the neonatal (10 days of age) and adult kidney (70-day-old rats) were studied. The neonatal kidney enzyme showed greater affinity, but less capacity than the adult enzyme to incorporate arachidonic acid into the membrane. The apparent K_m values were 27.8 and 73.9 µM while the v_max was 3.68 and 15.7 nmol/min/mg protein, for 10 and 70 days of age, respectively. Affinity for ATP was found to be almost 7-fold greater in adults when compared to neonates. The v_max for ATP also increased during development, with values of 1.04 and 2.87 at 10 and 70 days of age, respectively. Affinity for coenzyme A did not vary between the two stages studied, though the v_max increased 10-fold from 10 to 70 days of age. Since arachidonic acid availability is low in the perinatal stage because of its restricted endogenous synthesis, the higher enzyme affinity for this fatty acid at 10 days of age described here, could be of great importance in helping to capture the low but indispensable amount of arachidonic acid present in maternal milk during lactation.

Changes in Rat Papilla Microsomal Membrane Fluidity during Development

“…Taken together, our previous observations [4,21], the present results, and the other reports on membrane lipid-protein interaction support the possibility that the different physical behavior of 10-day-old membranes with respect to the adult membrane could, by altering the protein microenvironment, operate as a determining factor in the enzyme activity variations that characterize the immature kidney.…”

“…It is known that the lateral pressure, which increases with decreasing lipid order (increasing fluidity), can modulate the activity of certain membrane enzymes [20]. This is particularly important in the maturing kidney, since certain papillary membrane enzymes related to arachidonic acid metabolism, such as arachidonoyl coenzyme A synthetase and cyclooxygenase, are kinetically different, depending on the degree of kidney maturation [4,21]. Thus, arachidonoyl coenzyme A synthetase from 10-day-old microsomes possesses greater affinity, but less capacity, than that from adult, while cyclooxygenase, which is very active in the adult kidney, is highly inefficient in 10-day-old microsomes.…”