Analysis of substrates for DMSO reductase from Escherichia coli

A number of quinones, sulfoxides and amine oxides were chemically synthesized and tested as substrates for or inhibitors of Escherichia coli dimethyl sulfoxide (DMSO) reductase.;Methyl p-tolyl sulfoxide was reduced by DMSO reductase with a high stereospecificity, the (R)-enantiomer being the substrate. The (S)-isomer was neither a substrate nor an inhibitor of the enzyme. This specificity distinguishes E. coli DMSO reductase from the corresponding enzyme from Rhodobacter sphaeroides and suggests a different organization of the molybdenum cofactor in the enzyme active site.;The increase in volume of substituent groups in dialkyl sulfoxides led to the decrease of the binding affinity of a substrate to the enzyme, and dipropyl sulfoxide was not reduced. When reduced benzyl viologen was used as electron donor, some aliphatic amine oxides, unlike aromatic N-oxides and sulfoxides did not follow the Michaelis-Menten kinetics. The reduced form of 3-amino-2-methyl-1,4-naphthoquinone (AMNQH...