Schansker G, Goussias C, Petrouleas V, Rutherford AW. Reduction of the Mn cluster of the water-oxidizing enzyme by nitric oxide: formation of an S(-2) state.
Biochemistry 2002;
41:3057-64. [PMID:
11863444 DOI:
10.1021/bi015903z]
[Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The manganese cluster of the oxygen-evolving enzyme of photosystem II is chemically reduced upon interaction with nitric oxide at -30 degrees C. The state formed gives rise to an S = 1/2 multiline EPR signal [Goussias, Ch., Ioannidis, N., and Petrouleas, V. (1997) Biochemistry 36, 9261] that is attributed to a Mn(II)- Mn(III) dimer [Sarrou, J., Ioannidis, N., Deligiannakis, Y., and Petrouleas, V. (1998) Biochemistry 37, 3581]. In this work, we sought to establish whether the state could be assigned to a specific, reduced S state by using flash oxymetry, chlorophyll a fluorescence, and electron paramagnetic resonance spectroscopy. With the Joliot-type O(2) electrode, the first maximum of oxygen evolution was observed on the sixth or seventh flash. Three saturating pre-flashes were required to convert the flash pattern characteristic of NO-reduced samples to that of the untreated control (i.e., O(2) evolution maximum on the third flash). Measurements of the S state-dependent level of chlorophyll fluorescence in NO-treated PSII showed a three-flash downshift compared to untreated controls. In the EPR study, the maximum S(2) multi-line EPR signal was observed after the fourth flash. The results from all three methods are consistent with the Mn cluster being in a redox state corresponding to an S(-2) state in a majority of centers after treatment with NO. We were unable to generate the Mn(II)-Mn(III) multi-line signal using hydrazine as a reductant; it appears that the valence distribution and possibly the structure of the Mn cluster in the S(-2) state are dependent on the nature of the reductant that is used.
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