Reduction of aryl-nitroso compounds by pyridine and flavin coenzymes

Abstract

1. 1. A systematic kinetic investigation of the reduction of aryl-nitroso compounds by pyridine and flavin coenzymes and their analogs, in enzymatic and nonenzymatic systems, has been reported. 2. 2. Two main groups of nitroso compounds have been investigated, representatives nitroso-benzene and 1-nitroso-2-naphthol; in all enzymatic and nonenzymatic systems, the former was always reduced to phenyl-hydroxyl-amine and the latter to 1-amino-2-naphthol. 3. 3. Pyridine compounds included NADH, APAd-4H 2 and DBNA-4H 2 in nonenzymatic systems, and liver alcohol dehydrogenase. 4. 4. Flavin compounds included 1,5-dihydrolumiflavin and various forms of reduced S-ethyl-lumiflavin, in nonenzymatic systems, and the flavoenzymes glucose-oxidase and NADPH-cytochrome P450 reductase. 5. 5. Pyridine coenzymes and their analogs reduced nitroso compounds by a direct hydride transfer, with a primary kinetic isotope effect of 9.5 ± 2.2. 6. 6. All flavin compounds (glucose-oxidase and its nonenzymatic analog 1,5-dihydrolumiflavin and NADPH-cytochrome P450 reductase and its analog 5-ethyl-1,5-dihydrolumiflavin) reduced aryl-nitroso compounds with high efficiency ( k 2> 10 5M 5min −1). 7. 7. The flavin compounds have been shown to be much more efficient reductans of nitroso compounds, compared to pyridine coenzymes, both in enzymatic and nonenzymatic systems; the only exception to this rule presented the extremely efficient reduction of p-substituted aryl-nitroso compounds by liver alcohol dehydrogenase.