New Possibilities for Studying Mechanism of Nitrogenase Reaction with Photodonors of Electron

Abstract

Despite a great deal of research on the field of nitrogenase, the individual role(s) of the two types of metal-sulphur clusters (P and M) found in Av1 (MoFe protein) is not clear and the mechanism of charge separation following electron transfer against the potential from Av2 (Fe protein) to Av1 is unknown. One of the most promising ways of gaining this information appears to be photoreduction of nitrogenase over a microsecond range. An alternative electron donor for nitrogenase was developed (Druzhinin S. et al., 1993) based on photoexcited eosin with NADH. Some xanthene dyes were also studied as possible photodonors. Eosin, 4′,5′-dibromofluorescein, cyanosine, erythrosin are effective photodonors for nitrogenase, fluorescein and rhodamine B or 6G are not. The main difference between these active and inactive compounds was the high quantum yield of phosphorescence for active photodonors versus high quantum yield of fluorescence for inactive photodonors. All studied photodonors can inhibit electron transfer within nitrogenase following substrate reduction at high dye concentration. For 4′,5′-dibromofluorescein this concentration is 0,1 mM, for other dyes it is less. Under the same conditions the ATPase activity was inhibited to a significantly less degree. Optimal concentration of each xanthene dye as photodonor depends on its inhibition characteristics and varies in the range of 0,03–0,1 mM.