NO reversibly reduces the water-oxidizing complex of photosystem II through S-0 and S-1 to the state characterized by the Mn(II)-Mn(III) multiline EPR signal
N. Ioannidis et al., NO reversibly reduces the water-oxidizing complex of photosystem II through S-0 and S-1 to the state characterized by the Mn(II)-Mn(III) multiline EPR signal, BIOCHEM, 37(47), 1998, pp. 16445-16451
Incubation of photosystem II preparations with NO at -30 degrees C results
in the slow formation of a unique state of the water-oxidizing complex (WOC
), which was recently identified as a Mn(II)-Mn(III) dimer [Sarrou, J., Ioa
nnidis, N., Deligiannakis, Y., and Petrouleas, V. (1998) Biochemistry 37, 3
581-3587]. Evolution of the Mn(II)-Mn(III) EPR signal proceeds through one
or more intermediates [Goussias, C., Ioannidis, N., and Petrouleas, V. (199
7) Biochemistry 36, 9261-9266]. In an effort to identify these intermediate
s, we have examined the time course of the signal evolution in the presence
and absence of methanol. An early step of the interaction of NO with the W
OC is the reduction of S-1 to the S-0 state, characterized by the weak Mn-h
yperfine structure recently reported for that state. At longer times S-0 is
further reduced to a state which has the properties of the S-1 state, in t
hat single-turnover illumination restores the S-0 signal. The Mn(II)-Mn(III
) state forms after the S-1 state and is tentatively assigned to an (iso)S-
2 state, although lower states or a modified S-1 state cannot. be excluded
at present. Following removal of NO 60-65% of the initial S-2 multiline sig
nal size or the O-2-evolving activity can be restored. The data provide for
the first time EPR information on a state lower than S-0. Furthermore, the
low-temperature NO treatment provides a simple means for the selective pop
ulation of the S-0, S-1 and the Mn(II)-Mn(III) states.