Bile Salt Stimulated Human Milk Lipase Catalyzed Ester Hydrolysis in Detergentless Microemulsion Media

Abstract

Bile salt stimulated human milk lipase (E.C.3.1) has been used to catalyze the hydrolysis of 4-nitrophenylalkanoates (alkyl C-chain length, n = 2, 3, 4, 6, 10, 12 and 16) in a detergentless microemulsion medium of n-hexane/iso-propanol/water (71.1:27.7:1.2 vol%) containing 2 mM taurocholate at 37°C. The rate of hydrolysis of the esters with n = 2, 3, or 4 was nearly equal but the rate then fell rapidly with increasing alkyl-chain length. No activity was observed with the palmitate ester. Three dimensional surfaces were built up to represent both the catalytic activity and the rate constant of inactivation for the enzyme catalyzed hydrolysis of 4-nitrophenylpropionate in a range of compositions of the ternary system n-hexane/wo-propanol/water at 37 °C. Maximum activation and maximum inactivation were observed in the ternary region of the phase diagram. In the stable; transparent micro-emulsion region another smaller maximum in activity was observed and, at this same solvent composition, minimum inactivatio...