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Oxidation of excited-state NADH and NAD dimer in aqueous medium involvement of O2− as a mediator in the presence of oxygen

1984; Elsevier BV; Volume: 801; Issue: 3 Linguagem: Inglês

10.1016/0304-4165(84)90145-4

1872-8006

Barbara Czochralska, Wiesław Kawczyński, Grzegorz Bartosz, David Shugar,

Photosynthetic Processes and Mechanisms

It has been shown that direct excitation of NADH (or NADPH) in aqueous medium at 254 nm, or at wavelengths longer than 320 nm (where only the reduced nicotinamide moiety absorbs), leads to generation of NAD+ (or NADP+). The reaction proceeds both in the presence and absence of oxygen. Under aerobic conditions the reaction is accompanied by formation of H2O2 at a level equimolar with that of the NADH present in solution. On irradiation at wavelengths longer than 320 nm, conversion of NADH to enzymatically active NAD+ is about 75%. Under analogous irradiation conditions, the dimers (NAD)2 and (NADP)2 undergo disproportionation to NAD+ and NADP+, respectively, to the extent of 90%. Both physicochemical and enzymatic criteria were employed to formulate mechanisms for the photooxidation of NADH and the photodisproportionation of the dimer (NAD)2.