Kinetic properties of human milk bile salt-activated lipase: studies using long chain triacylglycerol as substrate.

Studies on the hydrodynamic properties of human milk bile salt-activated lipase (BAL) indicated that it is a monomer with molecular weight of 107,000. The presence of taurocholate (1 mM) did not lead to an association of the enzyme. The enzyme had a basal activity with trioctanoylglycerol and with shorter chain, but not with longer chain, monoacid triacylglycerols. Based on kinetic analyses, we suggest that the BAL-catalyzed lipolysis of long-chain triacylglycerol can be described to follow a compulsory sequential mechanism. The initial interaction of BAL with the activator (taurocholate) leads to a conformational change of the enzyme which facilitates the further interaction with the long chain triacylglycerol substrate in forming the enzyme-bile salt-substrate ternary complex. We also suggest that the binding of BAL with substrate involves direct interaction of the active site with the fatty acyl-chain of the triacylglycerol rather than with nonspecific hydrophobic interactions at the emulsion interface.