Properties of palmitoyl-CoA: monopalmitoyl-sn-glycerol 3-phosphate palmitoyltransferase from rabbit mammary gland

Caffrey, M.; Kinsella, J. E.

doi:10.1016/0020-711x(78)90005-8

Palmitoyl-CoA:monopalmitoyl-sn-glycerol 3-phosphate palmitoyltransferase (LPAT) in microsomes from lactating rabbit mammary tissue is apparently composed of 2 isoenzmic species ( alpha and beta ). The alpha isoenzyme was operative with monomeric substrates and inhibited by micelles, whereas the beta isoenzyme was active with micellar substrates only. Existence of these isoenzymes was indicated by a biphasic dependence of initial velocity on acceptor and enzyme concn. When LPAT- alpha alone was present in the microsomes, behaviour was typical of a monomer-specific enzyme. The 2 isoenzymes exhibited different thermal stabilities and differential stabilities to Tween 80. Apparent Km values of 2.4 and 200 mu M and V max. values of 13.2 and 90 nmol lysophosphatidate acylated mg protein -1 min-1 were obtained for the monomer and micellar enzyme specific activities, resp. Phosphatidic acid was the major product of the acyltransferase. Specific activity of palmitoyl-CoA thiolase in mammary microsomes was 1.6 nmol min-1 mg protein -1.