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 two for caprine and one 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 two caprine enzyme fractions were three distinct electrophoretic bands of molecular weights 66,100; 58,900; and 55,000. Electrophoretic patterns of the two 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 two distinct electrophoretic bands with molecular weights of 74,100 and 66,100, but poly aery lamide gel electrophoresis in the absence of sodium dodecylsulfate or β-mercaptoethanol revealed only one 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.