* To whom correspondence should be addressed.
Received April 21, 1998
A photodonor is considered as an alternative electron donor for nitrogenase. The kinetic mechanism of nitrogenase turnover is discussed. The turnover is initiated by the transfer of an electron to the enzyme and results in formation of a substrate molecule. The effective rate constant of concerted transfer of the first and the second electron from Av2 (Fe-protein) to Av1 (Mo-Fe-protein) and the rate constant of transfer of the second electron are 70 ± 7 and 116 ± 10 sec-1, respectively. The rate constant of the rate-limiting reaction--MgADP release during formation of the superreduced state of Av1 (*Av12-)--is 12 ± 2 sec-1. Nitrogenase (E) states in complex E·N2 on binding and reduction of nitrogen are: E2, E4, E6 (2, 4, and 6 electrons).
KEY WORDS: nitrogenase, Fe-protein, Mo-Fe-protein, photodonor, kinetic laser spectroscopy