Stimulation of the hormone-sensitive triacylglycerol lipase from adipose tissue by phosphatidylethanolamine

The activity of a pigeon adipose tissue hormone-sensitive triacylglycerol lipase preparation was increased from 2- to 5-fold by the presence of phosphatidylethanolamine in assays with three different methods of preparing triolein substrates. Phosphatidylethanolamine from egg yolk produced the greatest stimulation of lipase activity; the stimulation was concentration-dependent but was not time-dependent. A comparable increase in triacylglycerol lipase activity due to phosphatidylethanolamine was also observed with enzyme preparations from chicken and rat adipose tissue. Phosphatidylcholine, phosphatidylserine, phosphatidylinositol, phosphatidic acid, cardiolipin, sphingomyelin, Triton X-100 and sodium dodecyl sulfate all inhibited enzyme activity. Phosphatidylethanolamine had no effect on acid lipase activity in the pigeon adipose tissue preparation. Preincubation of the pigeon adipose tissue lipase with ATP, cyclic AMP and protein kinase resulted in a 2.15-fold activation of hydrolase activity determined in the absence of phosphatidylethanolamine. In contrast, non-activated and protein kinase-activated forms of the lipase were characterized as having very nearly the same activity in assays with substrate preparations containing phosphatidylethanolamine. The phosphatidylethanolamine-dependent stimulation of lipase activity was characterized kinetically as being due to an increase in maximal velocity. The modulation of the adipose tissue hormone-sensitive lipase activity by phospholipids could be involved in the hormonal regulation of lipolysis.