Heparin activation of soluble heart lipoprotein lipase

Abstract

Lipolytic activity of rat heart homogenates was increased 2 to 3 fold by addition of heparin in vitro. This effect was also evident on soluble fractions after 105,000 x g centrifugation. In characterizing this activity it was shown that heparin concentrations from 8 to 32 [mu]g/ml caused marked effects on lipolytic activity, whereas concentrations above 50 [mu]g/ml were less effective. Addition of epinephrine was without effect, whereas 0.5 NaCl resulted in complete inhibition of lipolysis. Highest total lipolytic activity was present in the nuclei and cell debris residue, but the highest specific activity resided in the microsomal fraction. However, of all cell fractions, only the nuclear-cell debris, and the 105,000 x g soluble fractions responded to addition of heparin. Since the soluble fraction is devoid of all known cell fractions, the heparin stimulation of Upolytic activity in this fraction could not be explained simply by release of bound lipoprotein lipase. Different properties of heparin-activated lipoprotein lipase and preheparin activity based on stability studies, adsorption on tricalcium phosphate gel, and differential purifcation by acetone fractionation support the suggestion that tissues contain an inactive form of lipoprotein lipase which becomes enzymatically active in the presence of heparin.