End group analysis of yeast fatty acid synthetase.

The purified yeast fatty acid synthetase complex has been subjected to amino and carboxyl terminal amino acid end group analysis. Amino end groups were studied by Edman degradation and by dansylation of the sodium dodecyl sulfate- or urea-denatured complex. No N-terminal amino acid could be identified by either method. C-terminal amino acids were investigated by tritium labeling and by digestion of the complex with carboxypeptidases A and B. By both methods, the two amino acids valine and lysine were consistently identified as the C-termini of two different polypeptide chains. After separation of the fatty acid synthetase subunits A and B by sodium dodecyl sulfate polyacrylamide gel electrophoresis lysine was identified as the C-terminus of subunit A and valine as that of subunit B. The results are interpreted as evidence that the yeast fatty acid synthetase complex is basically composed of two nonidentical and multifunctional polypeptide chains.