Purification and Properties of Dimethylsulfoxide Reductase Containing a Molybdenum Cofactor from a Photodenitrifier, Rhodopseudomonas sphaeroides f.s. denitrificans

Abstract

Dimethylsulfoxide (DMSO) reductase was purified to electrophoretic homogeneity from the periplasmic fraction of a photodenitrifier, Rhodopseudomonas sphaeroides f.s. denitrificans. The enzyme had a molecular weight of 82,000 and had no subunit. It contained 1 mol of molybdenum per mol of enzyme, but iron and acid-labile sulfur were not present. The UV-visible spectrum showed only one absorption maximum at 280 nm. Denaturation of the enzyme released a molybdopterin cofactor, the fluorescence spectra of which were almost the same as those of a form B derivative of molybdopterin found in formate dehydrogenase. The K_m value for DMSO was 15 μM, which was much lower than that for trimethylamin-N-oxide (TMAO), whereas V_max with TMAO was larger than that with DMSO.