Electron transferring flavoprotein of Peptostreptococcus elsdenii that functions in the reduction of acrylyl coenzyme A

Abstract

In P. elsdenii, (Megasphaera elsdenii) a three component flavoprotein electron transfer system catalyzes the oxidation of lactate and the reduction of crotonyl coenzyme A (CoA). Spectral evidence showed that D lactate dehydrogenase, when reduced by D lactate, was able to reduce butyryl CoA dehydrogenase but only in the presence of the electron transferring flavoprotein. Reduced nicotinamide adenine dinucleotide could replace reduced D lactate dehydrogenase. A reconstituted system, containing the three partially purified enzymes, excess D lactate, and a limiting amount of crotonyl CoA, reduced the crotonyl CoA to butyryl CoA, but only if all components were present. The electron transferring flavoprotein activity, purified 22 fold, was separated into two major flavoprotein components, A and B, after polyacrylamide gel electrophoresis. Elution of the proteins and subsequent kinetic assays of the eluates showed that component B catalyzes the reduction of butyryl CoA dehydrogenase by reduced D lactate dehydrogenase, whereas component A does not. Both A and B catalyzed the reduction of butyryl CoA dehydrogenase by reduced nicotinamide adenine dinucleotide. The results suggest that the D lactate dehydrogenase dependent reduction involves a heretofore unrecognized component of the electron transferring protein group which may utilize an unusual flavin, 6 hydroxy 7,8 dimethyl 10 (ribityl 5' adenosine diphosphate) isoalloxazine.