The arrangement and role of some of the amino acid residues in the beta-ketoacyl synthetase site of chicken liver fatty acid synthetase.

摘要: The beta-ketoacyl synthetase site of eukaryotic fatty acid synthetases is comprised in part a pantetheinyl residue on one subunit juxtapositioned with cysteinyl the adjacent subunit. present study has confirmed this arrangement and identified 2 additional residues site. active were as summarized below. Sodium borohydride reduction keto derivatives dibromopropanone cross-linked yielded alcohol which amenable to isolation good yields. enzyme primarily cysteinecysteamine derivative 2-propanol, demonstrating that cystyl by dibromopropanone. However, cold-inactivated enzyme, primary product cross-linking reaction was dicystyl derivative. In addition, between residues, but not two resulted subunits. Therefore, it proposed there are highly reactive toward alkylating agents at pH 6.5, suggesting presence cationic interacting thiolate anion. This proposal supported using bifunctional reagent o-phthalaldehyde found cross-link epsilon-amino group lysine pantetheinyl-SH or cystyl-SH form thioisoindole ring. dialdehyde inhibited inactivating activity, inhibition could be prevented malonyl-CoA lesser extent acetyl-CoA. Blocking thiol groups 5,5'-dithiobis(2-nitrobenzoic acid) reduced formation fluorescent close cystyl-SH, pantetheinyl-SH, led us propose positive may serve an electron sink general acid-catalyzed decarboxylation reaction.