Studies on the substrate specificity of purified human milk bile salt-activated lipase

The fatty acid specificity of the bile salt-activated lipase purified from human milk was studied using C12 to C54 (total acyl carbon) saturated and the C54 unsaturated triacylglycerols. Kinetic studies indicated that the short chain triacylglycerols were hydrolyzed more readily than the long chain triacylglycerols, and that the long chain unsaturated triacylglycerols were attacked more readily than the long chain saturated triacylglycerols. This fatty acid specificity was also apparent intramolecularly, both short chain and unsaturated fatty acids being released at higher rates than the saturated long chain acids. The enzyme possessed neither positional specificity nor stereospecificity as indicated by the nearly simultaneous appearance of the sn-1,2-, sn-2,3-, and sn-1,3-dioleoylglycerols from trioleoylglycerol. The hydrolyses of these three ester bonds were approximately at their anticipated chemical reactivities. Synthetic rac-1-monooleoylglycerols were hydrolyzed about 2 times faster than the sn-2-monooleoylglycerols. It is concluded that the bile salt-activated lipase may possess a special potential for a rapid release of short chain and polyunsaturated fatty acids from dietary triacylglycerols in the intestinal lumen of infants.