Lipolysis and lipid movement in a membrane model. Action of lipoprotein lipase.

The action of purified bovine milk lipoprotein lipase on tri[3H]oleoylglycerol and the effect of albumin on movement of lipolytic products at an argon-water interface were studied in a specially designed tricomparted trough. The amount of trioleoylglycerol applied was 14 times that needed to cover the surface of the aqueous subphase (0.1 M Tris . HCl, pH 7.4) with a monolayer. It is concluded that trioleoylglycerol was present in lenses on the surface of the aqueous subphase, that hydrolysis by lipoprotein lipase occurred in or near the lipid/argon-water interface, and that lipolytic products immediately located and spread throughout the interface, displacing substances with lower spreading pressures from the interface. Addition of albumin to the aqueous subphase accelerated markedly the desorption of oleic acid and monooleoylglycerol from the interface and thereby enhanced lipolysis. When albumin was not contiguous with the site of hydrolysis, oleic acid and monooleoylglycerol readily moved in the interface to the area of contact with albumin where they were desorbed from the interface. These findings support the hypothesis of transport of lipolytic products by lateral movement in cell membranes.