Inactivation of 3‐Oxoacyl Synthetase Activity of Pigeon Liver Fatty Acid Synthetase by S‐(4‐Bromo‐2,3‐dioxobutyl)‐coenzyme A

Abstract

Pigeon liver fatty acid synthetase was inactivated by treatment with S-(4-bromo-2,3-dioxobutyl)-CoA. This inactivation is fast, irreversible and dependent on both time and inhibitor concentration. It is also specific and selective a s only the 3-oxoacyl synthetase and acetyl-CoA transacylase component activities, out of the seven component activities possessed by the fatty acid synthetase complex, were inhibited. The binding of bromodioxobutyl-CoA to the enzymc is covalent as evidenced by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The modified enzyme showed characteristic absorption peaks at 266 nni and 315 nm that are identical to the absorption maxima of pure inhibitor. All the available evidence suggests that the mechanism of inhibition of fatty acid synthetase by S-(4-bromo-2,3-dioxobutyl)-CoA involved its binding to critical thiols, namely the cysteine -SH of the condensing enzyme and cysteamine -SH of the 4'-phosphopantetheine prosthetic group. Both substrates, acetyl-CoA and malonyl-CoA, also protected the enzyme against inhibition by S-(4-bromo-2,3-