Abstract
The regulation of triacylglycerol ester hydrolase (TG lipase) activity was studied in a pH 5.2 precipitate fraction from rat hearts. Neutral TG lipase activity (assayed at pH 7.5) was measured with both ethanolic and glycerol-dispersed triolein substrate preparations; acid lipase activity was determined at pH 5 with a glycerol-dispersed triolein substrate preparation containing lecithin. Neutral TG lipase activity was inhibited by free fatty acids (oleic acid) and by fatty acyl CoA compounds (oleoyl CoA, palmitoyl CoA); concentrations required for half-maximal inhibition were 100 μ m and 20 to 25 μ m, respectively. Palmitoyl carnitine resulted in an increase in neutral TG lipase activity. The inhibition of neutral TG lipase activity by oleoyl CoA could be prevented by increasing the content of albumin in the assay, and was reduced when the triolein substrate concentration was increased. Fatty acyl CoA compounds also inhibited acid TG lipase activity, but palmitoyl carnitine was the most effective inhibitor (concentration for half-maximal inhibition of 30 μ m). The inhibition of neutral TG lipase activity by fatty acyl CoA is consistent with the observation that metabolic interventions that increase tissue levels of fatty acyl CoA result in an inhibition of rates of cardiac lipolysis.
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