Evidence that the greening ligand in native butyryl-CoA dehydrogenase is a CoA persulfide.

Yellow butyryl-CoA dehydrogenase and general acyl-CoA dehydrogenase are "greened" by a mixture of coenzyme A plus elemental sulfur. The resultant stable complex contains an identical ligand with that present in native green butyryl-CoA dehydrogenase and has the same broad absorption band centered at 710 nm. Evidence is presented that the greening ligand is a CoA persulfide, possibly a mimic of the substrate carbanion thought to be generated early in the normal catalytic cycle. Variation in the position of the long wavelength band on replacement of FAD by a series of analogs of differing oxidation-reduction potential is consistent with a charge-transfer complex between a persulfide as the donor and oxidized flavin as the acceptor. The possible physiological and metabolic significance is discussed.