Nitric Oxide-Induced Formation of the S-2 State in the Oxygen-Evolving Complex of Photosystem II from Synechococcus elongatus†
journal contributionposted on 07.01.2003, 00:00 by Josephine Sarrou, Sabina Isgandarova, Jan Kern, Athina Zouni, Gernot Renger, Wolfgang Lubitz, Johannes Messinger
In spinach photosystem II (PSII) membranes, the tetranuclear manganese cluster of the oxygen-evolving complex (OEC) can be reduced by incubation with nitric oxide at −30 °C to a state which is characterized by an Mn2(II, III) EPR multiline signal [Sarrou, J., Ioannidis, N., Deligiannakis, Y., and Petrouleas, V. (1998) Biochemistry 37, 3581−3587]. This state was recently assigned to the S-2 state of the OEC [Schansker, G., Goussias, C., Petrouleas, V., and Rutherford, A. W. (2002) Biochemistry 41, 3057−3064]. On the basis of EPR spectroscopy and flash-induced oxygen evolution patterns, we show that a similar reduction process takes place in PSII samples of the thermophilic cyanobacterium Synechococcus elongatus at both −30 and 0 °C. An EPR multiline signal, very similar but not identical to that of the S-2 state in spinach, was obtained with monomeric and dimeric PSII core complexes from S. elongatus only after incubation at −30 °C. The assignment of this EPR multiline signal to the S-2 state is corroborated by measurements of flash-induced oxygen evolution patterns and detailed fits using extended Kok models. The small reproducible shifts of several low-field peak positions of the S-2 EPR multiline signal in S. elongatus compared to spinach suggest that slight differences in the coordination geometry and/or the ligands of the manganese cluster exist between thermophilic cyanobacteria and higher plants.