Substrate-dependent lipolysis induced by isoproterenol

The relationship between isoproterenol-induced lipolysis and the phosphoryl ation of perilipin and hormone-sensitive lipase (HSL) was examined using ce ll-free systems consisting of lipid droplets isolated from rat fat cells an d HSL, and/or trioleoylglycerol emulsified with gum arabic and HSL. Isoprot erenol was found to stimulate lipolysis in the cell-free system with the li pid droplets without an increase in the phosphorylation of either perilipin or HSL. On the other hand, no stimulation of lipolysis was found in the ce ll-free system containing lipid droplets despite increases in the phosphory lation of perilipin and HSL. In the cell-free system consisting of trioleoy lglycerol emulsified with gum arabic and HSL, neither isoproterenol nor inc reases in the phosphorylation of perilipin and HSL accelerated lipolysis, T hese results suggest that isoproterenol-induced lipolysis may not be mediat ed through the phosphorylation of perilipin and HSL, and may rather be depe ndent on the substrate of HSL. (C) 2000 Academic Press.