HEPATIC LIPASE ACYLATES DOLICHOL IN THE PRESENCE OF A PLASMA COFACTORIN-VITRO

Phosphatidylethanolamine:dolichol acyltransferase (PEDAT), an enzyme p reviously partially purified and characterized in rat liver [Sindelar, P., Chojnacki, T., & Valtersson, C. (1992) J. Biol. Chem. 267, 20594- 20599], is here purified to homogeneity from a heparin perfusate of ra t liver and is shown to be identical to hepatic lipase. However, in co ntrast to triglyceride hydrolysis by hepatic lipase, the PEDAT activit y is strongly dependent on a heat-stable plasma cofactor. This cofacto r stimulates the activity up to 15-fold and shifts the pH optimum for the reaction from 8.5 to 7.5. Upon gel filtration on Bio-Gel A-1.5, th e factor is heterogeneously distributed, with a major peak at 220 kDa. The dolichol-acylating activity can also be detected in rat adrenals and ovaries, and evidence is presented that the PEDAT assay shows a hi gher degree of specificity for hepatic lipase than the standard assay with triolein-gum arabic emulsion in 1 M NaCl.