Activatable cholesterol esterase and triacylglycerol lipase activities of rat adrenal and their relationship

Abstract

Activatable cholesterol esterase and triacylglycerol lipase of rat adrenal were 58–69% recovered in the 100 000 × g supernatant fraction. Activatable triacylglycerol lipase activity was differentiated from the activity of acid lipase and lipoprotein lipase also found in this fraction. Cholesterol esterase was activated 39.7 ± 13.6% (S.D.) and triacylglycerol liapse 11.9 ± 2.9% in a reaction dependent on ATP, cyclic AMP, and protein kinase. The two activities were shown by differential inhibition by an organophosphate, and by partial separation on salting out, to be largely due to separate enzymes. The two enzymes bound tightly to substrate emulsions with quantitatively similar distribution between competing emulsions, suggesting concerted binding. Coinciding gel filtration patterns reinforced, the hypothesis of a lipase complex. Cholesterol esterase comprised a major component of higher apparent K m for substrate and molecular weight 3 · 10 5–6 · 10 5 by gel filtration, and a minor component of lower apparent K m and heterogeneous molecular weight above 1 million, which was found mostly in complex with lipid.