Characterization of the flavoenzyme enoyl reductase of fatty acid synthetase from yeast.

Enoyl reductase in the fatty acid synthetase from brewer's yeast, a flavoenzyme function, has been used as a specific probe for one partial activity of the multi-functional enzyme. The enzyme has an absorption maximum at 460 nm with epsilon = 18600 M-1 cm-1 and A280 = 1.37 mg-1 ml. The circular dichroism spectrum shows negative peaks at 373 and 466 nm. The fluorescence maximum is at 540 nm. The apoenzyme has an absorption maximum at 279 nm and shows fluorescence at 345 nm. The association constant for the FMN is 4 X 10(7) M-1. The redox potential was determined as Eh = --0.193 V. The reductase is characterized as a 'true' transhydrogenase as no flavin free radical can be obtained by photochemical or chemical reduction or oxidation, i.e. it only functions via two-electron steps. An interpretation of the hydrophobic nature of the flavin binding site based on spectral data is presented.