Oscillations of the redox state of the nicotinamide adenine dinucleotide coenzime in an aqueous medium and in microemulsions upon interaction with an endogenous source of nitrogen oxide: S-nitrosoglutathione

Аннотация

The nicotinamide adenine dinucleotide (NADH) coenzime, which is involved in redox transformations in all living cells, fluoresces only in the reduced state. The degradation kinetics of its fluorescence in the reaction with the endogenous source of nitrogen oxide, S-nitrosoglutathione (GSNO), can be separated in two main stages: (i) a sharp decrease in intensity and (ii) a relatively slow exponential stage, against the background of which large-amplitude oscillations of signal intensity are observed. The degradation of NADH fluorescence in water-in-oil microemulsions of anionic surfactant based on sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol OT or AOT) occurs much more rapidly than in a homogeneous buffer solution. The relative contribution of the stepwise stage increases under illumination by a nitrogen laser (337 nm) and with the GSNO and water contents in the microemulsion. When there are on average one NADH molecule and one GSNO molecule per microemulsion bubble, the contribution of the stepwise stage ismuch smaller than for the samples with a lowerNADH content. The rate constant of the slow stage of NADH fluorescence degradation decreases under these conditions, whereas the intensity oscillation frequency increases. Large-amplitude oscillations of the NADH fluorescence intensity in microemulsions are more pronounced in the presence of a buffer (1mM HEPES, pH 7.4) than in pure water. The effects observed are assumed to be due to the shifts of local pH of the aqueous microenvironment of reagents in microemulsion bubbles and to the participation of buffer radical cations in the reduction of the intermediate radical NAD• to NADH.