Chicken liver fatty acid synthetase dimer: evidence of asymmetrical structure from iodoacetamide inhibition studies.

The condensing component of chicken liver fatty acid synthetase is inhibited by a sulfhydryl reagent, iodoacetamide, with a second-order rate constant of 0.23 M-1 sec-1 at pH 7.0 and 0 degrees. Complete inactivation requires the modification of approximately 8 -SH groups per dimer of the enzyme. Quantitation of the extent of inactivation in the presence of 1 mM acetyl CoA (which completely protects the enzyme against inactivation) and in its absence shows that complete inactivation results from the binding of approximately 1.1 mol of carboxamidomethyl residues per dimer. These data are consistent with the proposed functional asymmetry of the enzyme.