Subunit structure of Mycobacterium smegmatis fatty acid synthetase. Evidence for identical multifunctional polypeptide chains.

Fatty acid synthetase from Mycobacterium smegmatis has been purified to near homogeneity as judged by a variety of electrophoretic criteria under both native and dissociating conditions. A single protein band was obtained on gel electrophoresis in sodium dodecyl sulfate or 8 M urea at various pH values and on isoelectric focusing in 8 M urea. A subunit molecular weight of about 290,000 was found by polyacrylamide gel electrophoresis in sodium dodecyl sulfate or by sedimentation equilibrium ultracentrifugation in 6 M guanidine HCl. Quantitative Quantitative determination of pantetheine, of flavin, and of the number of fatty acids synthesized during a single enzyme turnover all yield values corresponding to a stoichiometry of about 1 mol per mol of subunit, providing strong evidence that M. smegmatis fatty acid synthetase is an oligomer of identical, multifunctional polypeptide chains.