A comparison of the lipolytic activities in liver perfusates and liver plasma membranes from rats

We have undertaken a study to resolve the conflicting reports on the substrate specificity of the lipolytic enzyme(s) released by heparin from liver and report the following:(1) Heparin perfusates from liver contain an enzyme(s) capable of degrading triacylglycerol, diacylglycerophosphoryl-ethanolamine and monoacylglycerol, whereas a heparin-solubilized fraction from liver plasma membranes hydrolyzes diacylglycerophosphorylethanolamine and monoacylglycerol only; (2) The lipolytic activities for the two sources behave differently on gel filtration but have the same behavior on heparin-Sepharose affinity chromatography; (3) Treatment of the preparation from the plasma membrane with Triton X-100 followed by heparin-Sepharose affinity chromatography produces forms of the enzyme(s) that now have activity on triacylglycerol. This study suggests that the enzyme(s) from the two sources may be the same and that some change occurs when the enzyme is released from the intact liver.