Purification and Partial Characterization of Caprine Milk Lipoprotein Lipase

Abstract

Lipoprotein lipases of caprine and bovine milks were isolated, purified and partially characterized from raw whole milk. Fractions with enzyme activity were 2 for caprine and 1 for bovine lipase. The milk lipoprotein lipase enzyme fractions were purified further by hydroxylapatite and intervent dilution chromatography. Caprine enzyme fractions were purified 142,000 and 87,000-fold from the isolates compared to the bovine enzyme, which was purified 5500-fold. For the 2 caprine enzyme fractions were 3 distinct electrophoretic bands of MW 66,100, 58,900 and 55,000. Electrophoretic patterns of the 2 fractions were similar. Isoelectric focusing of the highly purified caprine fractions also revealed heterogeneity with minor differences in isoelectric points, pH 5.02 and 5.14. Bovine enzyme had 2 distinct electrophoretic bands with MW of 74,100 and 66,100, but polyacrylamide gel electrophoresis in the absence of sodium dodecylsulfate or .beta.-mercaptoethanol revealed only 1 major band indicating a quaternary structure. The pH optimum of the caprine milk lipoprotein lipase was 8.7, compared to bovine enzyme of 8.5. Increase of yield of enzyme from both species during purification was attributed to several factors, the most important being the removal of an inhibitor. If in milk, this inhibitor may play a role in susceptibility of milk to hydrolytic rancidity.