Esterase and Lipase Activity of Hepatic Triglycerice Lipase in Post Heparin Plasma

The mechanisms of the triglyceride hydrolysis by hepatic triglyceride lipase (HTGL) were studied. Purified HTGL by affinity chromatography on heparin-Sepharose contained esterase activity, which hydrolized water soluble fatty acid ester, tributyrin as well as lipase activity which hydrolized triolein. The lipase activity was decreased by the addition by tributyrin, but esterase activity was enhanced by the addition of triolein emulsion, and dipalmitoylphosphatidylcholine (DPPC) vesicles. Kinetic analysis showed same Km values, and augmented Vmax values in the presence of DPPC vesicles. The enzyme was bound to the triolein emulsion even in the presence of tributyrin. These results indicated that HTGL has functionally two site; one is catalytic site, which hydrolizes ester bond, and the other is interface recognition site (IRS), and that the binding of the enzyme to lipid interface through ISR cause structural conformational change of the enzyme so as to increase the esterase activity, namely interfacial activation. Trypsin treatment caused a decrease in lipase activity with no change of esterase activity, and lost a process of interfacial activation. Binding capacity of the enzyme to DPPC vesicles was also decreased. These results indicated that trypsinsensitive protion was involved in IRS.