Abstract
1. 1. Palmitoy 1-CoA: monopalmitoyl-sn-glycerol 3-phosphate palmitoyltransferase (LPAT) in microsomes from lactating rabbit mammary tissue is apparently composed of two isoenzymic species, denoted α and β, respectively. 2. 2. The ga isoenzyme is operative with monomeric substrates and inhibited by micelles whereas the β isoenzyme is active with micellar substrates only. 3. 3. The existence of these isoenzymes was indicated by a biphasic dependence of initial velocity on acceptor and enzyme concentrations. 4. 4. When LPAT-α alone is present in the microsomes the behavior is typical of a monomer-specific enzyme. 5. 5. The two isoenzymes exhibited disparate thermal stabilities and differential sensitivities to Tween 80. 6. 6. Apparent K m values of 2.4μM, 200 μM, and V max values of 13.2 and 90nmoles lysophosphatidate acylated per mg protein per min were obtained for the monomer and micellar specific enzyme activities, respectively. 7. 7. Phosphatidic acid was the major product of the acyltransferase. 8. 8. The specific activity of palmitoyl-CoA thiolase in mammary microsomes was 1.6 nmoles per min per mg protein.
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