New fluorescence evidence that each peptide of fatty acid synthetase has a keto and an enoyl reductase domain with different affinities for NADPH.

A new graphical analysis of fluorescence enhancement produced by NADPH binding to fatty acid synthetase from the uropygial gland of goose showed that the enzyme contains two binding sites per monomer with different Kd values. The site with the lower Kd (1.3 microM) showed lower enhancement than that with the higher Kd (7 microM). After specific inactivation of the enoyl reductase of the enzyme with pyridoxal phosphate (Poulose, a. J., and Kolattukudy, P. E. (1980) ARch. Biochem. Biophys. 201, 313-321) only the low affinity binding site was found. Graphical analyses of the data strongly suggest that each peptide of fatty acid synthetase contains one keto reductase domain with low affinity for NADPH and one enoyl reductase domain with high affinity for NADPH.