Continuous dehydrogenation of a steroid with immobilized microbial cells: Effect of an exogenous electron acceptor

Abstract

Whole cells of Pseudomonas testosteroni, induced to synthesize steroid-transforming enzymes beforehand, have been immobilized by entrapment in polyacrylamide gel. The immobilized cells have then been used to catalyze the continuous Δ¹-dehydrogenation of Reichstein's substance S under various conditions in the presence of phenazine methosulfate (PMS), an electron acceptor for the cell-free Δ¹-dehydrogenase. The presence of PMS substantially increases the rate of reaction when fed with the steroid substrate to a continuous stirred tank reactor containing the immobilized cells. The operational half-life of the Δ¹-dehydrogenase activity of the cells, about 103 hr under the best operating conditions, is essentially unaffected by the presence of PMS. Though the acceleration of the reaction may be due to PMS-mediated passage of electrons from some component in the electron transport chain to molecular oxygen, the lack of a similar effect with methylene blue is consistent with the conclusion that PMS functions directly as the electron acceptor for the Δ¹-dehydrogenase.