No abstract

Reacting gastric and pancreatic lipases with mixed diethyl p-nitrophenyl phosphate/bile salt micelles resulted in a stoichiometric inactivation of these enzymes as tested on emulsified tributyroylglycerol and trioleoylglycerol as substrates. Diethyl p-nitrophenyl phosphate treated gastric lipases were also inactive on water-soluble p-nitrophenyl acetate, whereas the modified pancreatic lipase was still able to hydrolyze this water-soluble substrate. The binding of diethyl p-nitrophenyl phosphate modified pancreatic and gastric lipases to tributyroylglycerol/water interface was comparable to that of native lipases. The essential free sulfhydryl group of gastric lipases underwent no chemical changes due to the reaction with micellar diethyl p-nitrophenyl phosphate. All in all, these results indicate that, in both gastric and pancreatic lipases, the essential serine residue which was stoichiometrically labeled by this organophosphorus reagent is involved in catalysis and not in lipid binding.

A glycerol-ester hydrolase was purified to homogeneity from porcine intestinal mucosa using a partial delipidation method and an eight-step purification procedure. The isolation scheme used gave a 483-fold purification, resulting in a pure enzyme with a specific activity on tributyrin of 290 µmol · min Ϫ1 · mg Ϫ1 . The molecular mass of the enzyme was estimated at 240 kDa, based on the results of size-exclusion chromatography, and at 60 kDa, as determined by SDS/PAGE analysis. The isoelectric focusing data obtained indicated that only one isoform with a pI of 5.1 was present. Complete identity was found to exist between the N-terminal sequence of the first 25 amino acid residues and that of a porcine liver carboxylesterase. A full-length cDNA coding for the enzyme was isolated from pig small intestine. We observed that the corresponding protein originally named intestinal glycerol-ester hydrolase definitely belongs to the carboxylesterase family. The deduced amino acid sequence consisted of 565 residues and showed 97% identity with that of porcine liver carboxylesterase and more than 50% identity with those of other carboxylesterases from different mammalian species.