Assay of lipoprotein lipase and hepatic lipase

Abstract Lipoprotein lipase (LPL) and hepatic lipase (HL) are two key enzymes in the metabolism and interconversion of lipoproteins (1-3; Table 1). The reactions occur at endothelial surfaces of blood vessels, where the enzymes are attached by interaction with polyanions, probably heparan sulphate proteo glycans anchored in the endothelial cell membrane (4). LPL appears all over the vascular bed of most extrahepatic tissues, though in varying amounts, while HL is localized at the liver and some steroid hormone producing glands. LPL acts mainly on the triglycerides of chylomicra and VLDL. The released fatty acids are taken up by nearby cells or are circulated in blood as albumin bound free fatty acids. LPL is under metabolic and hormonal control. HL acts mainly on smaller lipoproteins (HDL, IDL, chylomicron remnants). Its function is not yet fully understood. Some animal species, e.g. guinea pigs and cows, have little or no HL. HL is regulated by steroid hormones, but does not seem to be metabolically regulated.