MECHANISMS OF CHOSEN ENZYME REACTIONS - New Trends in Enzyme Catalysis and Biomimetic Chemical Reactions - page 88

) and its
component were performed (Druzhinin et al., 1993, 1995, 1996, 1989, 1998; Syrtsova et
al., 1995, 1998, 2000; Syrtsova and Timofeeva, 2001). In the case of the photodonor
eosin in the presence of NADH, the reducing agent for nitrogenase is the radical anion
with E 0 for the transition photodonor photodonor radical anion equal to -0.58 V
(Chan and Bolton, 1980), which is sufficient for reducing the cluster of
Av2 to the state in the successive transfer of two electrons. Stages of the
transfer of the first and second electrons in nitrogenase were detected by kinetic laser
spectroscopy using the photodonor system DBF—NADH in the presence of nitrogen
(Syrtsova et al., 2000).

A series of experiments on photoreduction of nitrogenase complex (Av2 Av 1

It has been established (Druzhinin et al., 1995) that, in the case of the photochemical
eosin—NADH system and dithionite concentrations not higher than

the

Av 1 •Av2 complex (1:1) is enzymatically active. The slow process

at 20 °C) of nitrogenase dissociation to the Av

and Av2 components was not
observed. The rate constant of a second order for the reduction of Av2 in the nitrogenase
complex with the eosin—NADH photodonor was found to be equal to
The relative positions of the metalloclusters indicate that electron transfer from FeP
to FeMoco procees through the P-clusters. The edge-edge distances between FeP and P-
cluster and between P-cluster and FeMoco were found to be about 14 Å (Schindelin et

1