N-(5-dimethylaminonaphthalene-1-sulfonyl)-3-aminobenzene boronic acid as an active-site-directed fluorescent probe of lipoprotein lipase

Inhibition of hepatic lipase by m-aminophenylboronate. Application of phenylboronate affinity chromatography for purification of human postheparin plasma lipases

Phenylboronates are competitive inhibitors of serine. hydrolases including lipases. We studied the effect of m-aminophenylboronate on triglyceride-hydrolyzing activity of hepatic lipase (EC 3.1,1.3). m-Aminophenylboronate inhibited hepatic lipase activity with a Ki value of 55 microM. Furthermore, m-aminophenylboronate protected hepatic lipase activity from inhibition by di-isopropyl fluorophosphate, an irreversible active site inhibitor of serine hydrolases. Inhibition of hepatic lipase activity by m-aminophenylboronate was pH-dependent. The inhibition was maximal at pH 7.5, while at pH 10 it was almost non-existent. These data were used to develop a purification procedure for postheparin plasma hepatic lipase and lipoprotein lipase. The method is a combination of m-aminophenylboronate and heparin-Sepharose affinity chromatographies. Hepatic lipase was purified to homogeneity as analyzed on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The specific activity of purified hepatic lipase was 5.46 mmol free fatty acids h-1 mg-1 protein with a total purification factor of 14,400 and a final recovery of approximately 20%. The recovery of hepatic lipase activity in m-aminophenylboronate affinity chromatography step was 95%. The purified lipoprotein lipase was a homogeneous protein with a specific activity of 8.27 mmol free fatty acids h-1 mg-1. The purification factor was 23,400 and the final recovery approximately 20%. The recovery of lipoprotein lipase activity in the m-aminophenylboronate affinity chromatography step was 87%. The phenylboronate affinity chromatography step can be used for purification of serine hydrolases which interact with boronates.

Diethyl-p-nitrophenyl phosphate: an active site titrant for lipoprotein lipase

Diethyl-p-nitrophenyl phosphate is an active site-directed irreversible inhibitor of bovine milk lipoprotein lipase catalyzed hydrolysis of the water-soluble substrate, p-nitrophenyl butyrate. Interaction of lipoprotein lipase and the inhibitor in the absence of substrate gives a biphasic kinetics profile, which is consistent with rapid formation of a phosphoryl-lipoprotein lipase intermediate which hydrolyzes slowly. The magnitude of the absorbance increase accompanying formation of the intermediate provides an analytical method for determining lipoprotein lipase active site concentration.

Comparison of acyl-oxyester and acyl-Thioester lipids as substrates for bovine milk lipoprotein lipase

The dithioester analog of dihexanoylphosphatidylcholine, rac-1,2-S,S-dihexanoyl-3-phosphocholine-1,2-dimercapto-3-propanol was synthesized and compared to the corresponding acyl-oxyester lipid as a substrate for bovine milk lipoprotein lipase. The apparent maximal reaction velocity (Vmax) for dihexanoyldithiophosphatidylcholine was considerably lower than that for dihexanoylphosphatidylcholine (0.12 vs. 5.0 mumol product released/min per mg lipoprotein lipase, respectively). The apparent Km values were 1.9 and 4.0 mM, respectively. 3-Butyrylthio-1,2-dibutyryloxypropane was also compared to tributyrylglycerol as a substrate for lipoprotein lipase; hydrolysis of the acyl-thioester bond was insignificant when compared to the corresponding oxyester derivative. Apolipoprotein C-II, the activator protein of lipoprotein lipase for long-chain fatty acyl substrates, had no effect on the hydrolysis of either the thio- or oxyester short-chain substrates. The low lipoprotein lipase activity for the thioester substrates is discussed in relation to the structure of the lipid and the active site of the enzyme.