Localization of the central and peripheral SH-groups on the same polypeptide chain of yeast fatty acid synthetase

Purified fatty acid synthetase isolated from wild type yeast cells as well as from two different $\text{fas}$-mutant strains was reacted with (1-¹⁴C-)iodoacetamide. Tryptic digests of the ¹⁴C-carboxamidomethylated enzymes were fractionated on Sephadex G-50. Hereby, essentially only one radioactively labeled peptide was eluted from the column. From this it is concluded that under the experimental conditions employed only the “peripheral” SH-group of yeast fatty acid synthetase becomes alkylated. By sodium dodecylsulfate-polyacrylamide gel electrophoresis of the ¹⁴C-carboxamidomethylated fatty acid synthetase it was shown that in all three enzyme preparations studied the inhibitor is bound to the larger one of the two fatty acid synthetase subunits. These findings indicate that the larger fatty acid synthetase subunit accomodates not only the “central” but also the “peripheral” SH-group of the multienzyme complex.