Green butyryl-coenzyme A dehydrogenase. An enzyme-acyl-coenzyme A complex.

1. Butyryl-CoA dehydrogenase from Peptostreptococcus elsdenii forms very tightly bound complexes with various acyl-CoA compounds. Spectra in some cases merely show resolution of the 450nm band, but those with acetoacetyl-, pent-2-enoyl- and 4-methylpent-2-enoyl-CoA show long-wavelength bands similar to the 710nm band of native enzyme. These complexes are formed instantaneously by the yellow form of the enzyme and much more slowly by the green form. 2. An acid extract of the green enzyme reconverts the yellow into the green form. 3. Hydroxylamine makes irreversible the otherwise reversible conversion of the green enzyme into the yellow form by phenylmercuric acetate. 4. Amino acid analysis for taurine and beta-alanine shows approx. 1mol of CoA/mol of flavin in green enzyme. Anaerobic dialysis of reduced enzyme removes the CoA. On acid precipitation of green enzyme the CoA is found only in the supernatant. 5. It is concluded that native green enzyme is probably complexed with unsaturated acyl-CoA. This is shown to be consistent with findings of other workers. Catalytic activity requires displacement of the acyl-CoA, which is therefore likely to be a potent inhibitor. 6. An explanation is offered for the irreversible conversion of green into yellow enzyme by sodium dithionite. 7. The enzyme displays a feeble, previously undetected, activity towards beta-hydroxybutyryl-CoA. 8. The product of oxidation of pent-4-enoyl-CoA forms a complex with reduced enzyme and strongly inhibits reoxidation of the FAD. This may contribute to inhibition of fatty acid oxidation by pent-4-enoic acid in mammals.