Evaluation of electron mediators for the electromicrobial reduction of chloropyruvate by Proteus vulgaris cells

Different electron mediators were evaluated for the electromicrobial reduction of chloropyruvate to chlorolactate. The reaction was catalyzed by a mediator-dependent D-lactate dehydrogenase in whole cells of Proteus vulgaris and yielded D-(S)-chlorolactate with high optical purity (> 97% e.e.). The ideal mediator should favor a high rate in the enzymatic reaction and a low rate in the nonenzymatic dehalogenation of the substrate. The latter reaction causes the formation of pyruvate and subsequently lactate. Viologens as mediators provided better yields than cobalt sepulchrate, safranine O, and an anthraquinone derivative. The best results were obtained with 1,1'-carbamoylmethylviologen as mediator. (C) 1997 by Elsevier Science Inc.