Milk lipoprotein lipases: a review

Area of Science:

• Biochemistry
• Enzymology

Background:

• Lipoprotein lipase (LPL) activity is present in milk across species, likely originating from mammary gland leakage.
• LPL facilitates the transfer of fatty acids from blood lipoproteins to milk triacylglycerols.

Purpose of the Study:

• To purify and characterize lipoprotein lipase from bovine skim milk.
• To investigate the enzyme's properties, including molecular weight, inhibitors, activators, and substrate specificity.

Main Methods:

• Extensive purification of bovine milk LPL using affinity chromatography (7000-fold purification).
• Analysis of enzyme characteristics, including molecular weight determination and assessment of inhibition and activation by various agents.
• Evaluation of substrate specificity, including stereospecificity and activity towards monoacylglycerols.

Main Results:

• Bovine skim milk is a rich source of LPL, purified to homogeneity.
• The enzyme has a molecular weight of approximately 62,000 Da and is inhibited by protamine sulfate, high salt concentrations, apolipoprotein C-I, and apolipoprotein C-III.
• Activation is observed with apolipoprotein C-II, serum, and heparin, to which the enzyme binds.
• The lipase shows specificity for primary esters of acylglycerols, with a preference for the sn-1 position, and also acts on 1-monoacylglycerols.
• Human milk contains a serum-stimulated LPL similar to bovine LPL, plus a bile salt-stimulated enzyme resembling sterol ester hydrolase.

Conclusions:

• Bovine milk LPL is a well-characterized enzyme with significant implications for milk fat metabolism.
• Comparative analysis with human milk LPL highlights species-specific variations and similarities.
• The study provides a comprehensive understanding of LPL's role and properties in milk.