Hydrolysis of tri- and monoacylglycerol by lipoprotein lipase: evidence for a common active site

Abstract

The relationship between triacylglycerol and monoacylglycerol hydrolyzing activities of purified rat heart lipoprotein lipase [EC 3.1.1.34] was studied using emulsified trioleoylglycerol and micellar on albumin-bound monooleoylglycerol as substrates. The maximal reaction rates obtained with the 2 substrates were similar (650 and 550 nmol of fatty acid released/min per mg protein, respectively). Addition of apolipoprotein C-II or serum increased the maximal reaction rate for the trioleoylglycerol hydrolyzing activity about 4-fold, but had no effect on the monooleoylglycerol hydrolyzing activity. Hydrolysis of the 2 substrates apparently takes place at the same active site of the enzyme since mutual competitive inhibition between the substrates could be demonstrated; the rate of inactivation of enzymatic activity with the 2 substrates in 1.2 M NaCl was the same, similar losses of hydrolytic activity with tri- and monooleoylglycerol were observed in the presence of low concentrations of n-butyl(p-nitrophenyl)carbamide and inhibition of both hydrolytic activities by this compound could be prevented by prior exposure of lipoprotein lipase to either substrate.