<p> A number of anaerobic and microaerophilic species lack pyruvate dehydrogenase and have instead a four subunit, oxygen-sensitive pyruvate oxidoreductase, with either ferredoxins or flavodoxins used as the acceptor. Several related four-subunit enzymes may exist in the same species. This entry describes the delta subunits, representing mostly pyruvate, 2-ketoisovalerate, and 2-oxoglutarate specific enzymes. The delta subunit is the smallest and resembles ferredoxins.</p> 2-oxoacid:acceptor oxidoreductase, delta subunit, pyruvate/2-ketoisovalerate