Acetoacetyl-CoA reductase activity of lactating bovine mammary fatty acid synthase.

P. F. Dodds, M. G. Guzman, S. C. Chalberg, G. J. Anderson, S. Kumar

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29 Scopus citations

Abstract

Fatty acid synthase, purified from lactating bovine mammary gland, utilizes coenzyme A esters of acetoacetic, 3-hydroxybutyric, and crotonic acids as substrates for its partial reactions at micromolar concentrations. The NADPH:acetoacetyl-CoA reductase had a Km of 5 microM acetoacetyl-CoA and a Vmax of about 4 mumol of NADPH oxidized min-1 mg-1. In contrast, the Km for the model compound, acetoacetyl pantetheine was 820 microM and that of S-acetoacetyl-N-acetylcysteamine was over 40 mM. The reduction of acetoacetyl-CoA was observed with the enzyme from rat tissues also but not with those from avian tissues or yeast. With the bovine mammary enzyme, the reaction was found to oxidize 2 mol of NADPH for every mol of acetoacetyl-CoA consumed. Butyrate was the major product of reduction. The reductase activity was susceptible to inhibition by several sulfhydryl reagents; it was lost when the synthase was dissociated into one-half molecular weight subunits or when the incubation mixture was depleted of CoA. It was competitively inhibited by acetyl-CoA, butyryl-CoA, methylmalonyl-CoA, and 2-methylcrotonyl-CoA. These results as well as its use as a primer in fatty acid synthesis by the enzyme suggest that the acetoacetyl group from acetoacetyl-CoA is transferred to the enzyme, presumably to its 4'-phosphopantheine prosthetic group. The acyl group is then expected to remain attached to the enzyme while it is reduced, dehydrated, and reduced again to form a butyryl group which can either undergo chain elongation, if malonyl-CoA is present, or be released from the enzyme by hydrolysis or transfer to free CoA.

Original languageEnglish (US)
Pages (from-to)6282-6290
Number of pages9
JournalJournal of Biological Chemistry
Volume256
Issue number12
StatePublished - Jun 25 1981

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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    Dodds, P. F., Guzman, M. G., Chalberg, S. C., Anderson, G. J., & Kumar, S. (1981). Acetoacetyl-CoA reductase activity of lactating bovine mammary fatty acid synthase. Journal of Biological Chemistry, 256(12), 6282-6290.