MILK LIPOPROTEIN LIPASES - REVIEW

Lipoprotein lipase activity was found in the milks from several species where it is assumed to result from leakage from the mammary gland into milk. The frunction of the enzyme in the gland is apparently to assist in the transfer of blood lipoprotein triacylglycerol fatty acids into milk triacylglycerols. Bovine skim milk, one of the richest sources of lipoprotein lipase, was purified 7000 fold by affinity chromatography. The lipase has a MW of .apprx. 62,000 and is inhibited by protamine sulfate, 1.0 M NaCl, apolipoprotein C-I (apolipoprotein-serine) and apolipoprotein C-III (apolipoprotein-alanine). The enzyme is activated by apolipoprotein C-II (apolipoprotein-glutamic acid), serum and heparin to which it also binds. The lipase is highly specific for the primary esters of acylglycerols and exhibits a slight stereospecificity for the sn-1 ester in preference to the sn-3-ester. Bovine milk also has separate activity toward 1-monoacylglycerols. Human milk contains a serum stimulated lipoprotein lipase with many of the characteristics of the enzyme in bovine milk, and an enzyme stimulated by bile salts which resembles the sterol ester hydrolase or rat pancreatic juice. The assay, function, purification, characteristics and substrate specificities of these enzymes are discussed.