[Free-radicals formation in reductions of flavin. Study on the reduction of aminoethylcellulose-bound flavin]. / Svobodnye radikaly v reaktsii vosstanovleniia flavina. Nzuchenie Vosstanovleniia flavina, prishitogo na aminoetiltselliulozy

The reduction of flavin by reduced diphosphopyridine nucleotide and photoreduction were studied spectrophotometrically. Flavin was covalently bound to aminoethylcellulose, therefore the interaction between flavin molecules was excluded. Nevertheless a considerable quantity of free radicals was demonstrated under these conditions. The experimental dependence of the radical concentration as a function of reduction degree is readily explained if the reduction of flavin proceeds in two consecutive one-electron steps. The ratio of the rate constants of both reactions for the reduction of flavin by NADH k2'/k1' was equal to 4, for the photoreductions k2'/k1' to 6.5.

[Free radicals in the flavin reduction reaction. Interaction of reduced nicotinamide adenine dinucleotide with flavin in solution]. / Svobodnye radikaly v reaktsii vosstanovleniia flavina. Izuchenie reaktsii vzaimodeistviia vosstanovlennogo nikotinamidadenindinukleotida s flavinom v rastvore

The study of the flavin mononucleotide (FMN)-reduced nicotinamide adeninedinucleotide (NADH) reaction was carried out both under aerobic and anaerobic conditions, using spectrophotometric and titrimetric methods. The consumption of NADH was shown to exceed two times the consumption of FMN in the anaerobic reaction and the rate constant in the aerobic reaction was found to be about 4 times of that of the anaerobic reaction. Moreover, the replacement of anaerobic conditions by aerobic ones at pH 5.0 resulted in a considerable increase of proton consumption rate in the reaction course. The data obtained are contradictory to the generally accepted hypothesis of hydrid-ion transfer in the reaction of NADH oxidation. It was assumed that this reaction proceeded through a homolytic pathway.