Dimethylsulphoxide and trimethylamine oxide respiration of Proteus vulgaris. Evidence for a common terminal reductase system.

Dimethylsulphoxide (DMSO) and trimethylamine oxide (TMAO) sustained anaerobic growth of Proteus vulgaris with the non-fermentable substrate lactate. Cytoplasmic membrane vesicles energized by electron transfer from formate to DMSO displayed anaerobic uptake of serine, which was hindered by metabolic inhibitors known to destroy the proton motive force. This showed that DMSO reduction was coupled with a chemiosmotic mechanism of energy conversion; similar data for TMAO respiration have been presented previously. All biochemical tests applied indicated that the oxides were reduced by the same reductase system. The DMSO and TMAO reductase activities showed the same mobility on ion-exchange chromatography, and polyacrylamide disc gel electrophoresis (pH 8.9), gradient gel electrophoresis, and gel isoelectric focusing; mol. wt. and pI determined were 95,000 and 4.6, respectively. DMSO inhibited reduction of [14C]TMAO in vesicles. The reductase was inducible to a certain extent; both oxides being equally efficient as inducers. TMAO was reduced at a higher rate than DMSO, explaining faster growth of cells and increased uptake of serine in vesicles with TMAO as electron acceptor. Comparative studies with Escherichia coli also gave evidence for common TMAO and DMSO reductase systems.