Hydrolysis of human plasma high density lipoprotein2-phospholipids and triglycerides by hepatic lipase

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Summary

To determine the physiological role of hepatic lipase in lipoprotein metabolism, human plasma very low (VLDL), low (LDL) or high (HDL2 and HDL3) density lipoproteins were labeled with [14C] triolein or [14C] dipalmitoyl phosphatidylcholine and the rates of lipid hydrolysis were determined using human heparin-releasable hepatic lipase. Compared to LDL and HDL3, HDL2 phospholipids were the preferred substrate for hepatic lipase; 17% of HDL2 phospholipids were hydrolyzed. [14C] Triolein-labeled HDL2 were also hydrolyzed by hepatic lipase. However, purified bovine milk lipoprotein lipase had negligible activity on HDL2-triglycerides. After incubation of HDL2 with hepatic lipase, there was a decrease in the size of the particle as demonstrated by gel filtration and an increase in the density as shown by zonal ultracentrifugation. These results suggest that hepatic lipase may play a role in the interconversion of HDL subfractions.

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