INHIBITION OF THE LIPASE FROM PSEUDOMONASSPEC. ATCC 21808 BY DIETHYL p-NITROPHENYL PHOSPHATE. HINTS FOR ONE BURIED ACTIVE SITE FOR LIPOLYTIC AND ESTEROLYTIC ACTIVITY

Abstract

Lipases have been shown to beserine-hydrolasessince they are inhibited by serine active reagents such as phenylmethylsulfonylfluoride (PMSF), boronic acids and organophosphates [1,2,3]. Furthermore, they are surface active enzymes,i.e. they are activated by binding to interfaces [4] comprising their natural substrates, the micelles of long chain fatty acid triglycerides. It has long been postulated that lipases undergo a conformational changein this activation process. Recently it became obvious from x-raystudies [1,5] that the active site is inaccessible to voluminoussubstrates unless a conformational change occurs sincethe active site is buried undera lid formed by a long peptide loop. The lipase from human pancreas presumably hydrolysessoluble substrateslike p-nitrophenyl acetate (pNPA)at a different site [5]. For the porcine pancreatic lipase it was reported that the C-terminal peptide fragment (336-449) shows the sameactivity towards pNPA as the complete enzyme but no activity towards triacylglycerols [6]. Whereas,in the triglyceride hydrolysis Ser-152 is involved [R. Verger, pers. communication]. Ourinhibition studies suggest that only one active site for both types of substrates exists for the lipase from Pseudomonas spec. ATCC 21808 and thatthis site is buried.