Reciprocal effect of apolipoprotein C-II on the lipoprotein lipase-catalyzed hydrolysis of p-nitrophenyl butyrate and trioleoylglycerol.

Interaction of purified bovine milk lipoprotein lipase (LpL) with sonicated vesicles of dipalmitoyl phosphatidylcholine in the gel phase is associated with an increase in the rate of the LpL-catalyzed hydrolysis of p-nitrophenyl butyrate. There is a 6-fold increase in Vmax. Apolipoprotein C-II, the activator protein for LpL, inhibits the LpL-catalyzed hydrolysis of p-nitrophenyl butyrate. With 0.5 mol % tri[14C]oleoylglycerol present in the dipalmitoyl phosphatidylcholine vesicles and in the presence of 20 mM Ca2+, the rate of p-nitrophenyl butyrate hydrolysis is decreased reciprocally compared to trioleoylglycerol hydrolysis and is dependent on apolipoprotein C-II. These results suggest that apolipoprotein C-II enhances the activity of LpL by increasing the affinity of the active site of LpL for triacylglycerol.