A kinetic study of neutral and alkaline triglyceride lipase activities from different liver homogenate fractions is reported. Lipase activities are studied with triolein as substrate and are determined by quantification of the released oleic acid liberated. Heparinreleasable, microsomal and mitochondrial lipase activities are studied as a function of time, protein concentration and substrate concentration. The neutral triglyceride lipase associated with mitochondrial membranes is kinetically different from the alkaline lipase, localized on the plasma membrane, which probably contaminates microsomal and soluble fractions.

An assay is described for the determination of lipase activity, using as substrate an emulsion of radioactive triolein with cholic acid as emulsifier. Lipase activity is given by determining radioactive triolein disappearance after incubation with the artificial emulsion. The catalytic activity of this enzyme has been studied with respect to time, protein concentration and substrate concentration. Under the experimental conditions, Michaelis constant value was 14.54 mmol/1 and maximal hydrolysis rate 0.31 μmol h^-1 mg^-1.