The reaction of chicken liver fatty acid synthetase with 5,5'-dithiobis(2-nitrobenzoic acid).

Abstract Chicken liver fatty acid synthetase is rapidly inhibited by 5,5′-dithiobis(2-nitrobenzoi acid). The inhibition results from the reaction of 5,5′-dithiobis(2-nitrobenzoic acid) with the cysteine-SH residue of the β-ketoacyl synthetase site. The adjacent pantetheine-SH of the other subunit displaces 2-nitro-5-thiobenzoic acid from the mixed disulfide resulting in the formation of a disulfide bond between the two residues and thereby cross-linking the two subunits. Scatchard analysis of the 5,5′-dithiobis(2-nitrobenzoic acid) inhibition indicated that there are two β-ketoacyl synthetase sites in the homodimer. The mixed disulfide formed between the pantetheine-SH and the cysteine-SH was reduced by 2-mercaptoethanol resulting in restoration of enzyme activity.