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Low temperature interactions of NO with the S1 and S2 states of the water oxidising complex of photosystem II. A novel Mn-multiline EPR signal derived from the S1 state
Journal of Inorganic Biochemistry
G14
MANGANESE
207
LOW TEMPERATURE INTERACTIONS OF NO WITH THE Sl AND Sz STATES OF THE WATER OXIDISING COMPLEX OF PHOTOSYSTEM II. A NOVEL MN-MULTILINE EPR SIGNAL DERIVED FROM THE S1 STATE.
Charilaos Goussias, Nikolaos Ioannidis, and Vasili Petrouleas Institute of Materials Science, NCSR "'Democritos ", 15310 Aghia ParaskevLAthens, Greece The active site of the water oxidising complex of Photosystem II (PSII) is thought to be a cluster of four manganese atoms. During sequential absorption of photons by PSII the water oxidising complex undergoes four one-electron oxidation steps, S0-S~,..,$3-$4, coupled to the release of molecular oxygen. PSII centers after a period of dark adaptation relax in the majority to the SI state. It is generally agreed that this is an integer spin state. Single electron oxidation of $1 produces the half-integer-spin $2 state, which is EPR active and gives a characteristic multiline signal at 1.He temperatures [ 1] and under certain conditions an alternative signal at g=4.1 [2,3]. These signals and variants of them have been valuable in assaying and understanding basic features of the complex. In earlier studies it was shown that NO binds reversibly to the PSII acceptor side non-heme Fe 2+ producing a characteristic EPR signal at g=4, and also to tyr YD" producing an EPR silent species [4]. The latter interaction, which is fast and reversible, is slowly succeeded by the formation of a nitrosotyrosine complex [5]. This acts as a donor to PSII and can be oxidised by light to an iminoxyl radical. I an extension of these studies we have noted that N O interacts rapidly with the $2 state of the water oxidising complex at temperatures as low as -75 °C, to yield an EPR silent state. NO also interacts with the dark-stable S~ state but at a much lower rate. At -30 °C and in the presence of approx. 0.5 - 0.7 mM N O S~ loses the ability to yield by illumination an EPR active $2 state with an approximate half-time of 40-60 min. At longer incubation times (tl/2 4-5 h) an intense new multiline signal develops. The new signal has a hyperfine splitting similar to the S2-multiline but is characterised by intense lines on the high field side. The N O modified Si state can act as a low temperature electron donor yielding an EPR silent state upon illumination at 200 K. The new multiline signal is attributed to binding and magnetic interaction of N O with Sl to produce a half integer spin state with a S--1/2 ground state. The unusual reactivity of the Mn cluster with NO, which implies at least two binding sites of N O is correlated with the chloride site and the binding of ammonia, and by extension, with substrate binding. 1. Dismukes, G.C., & Siderer, Y. (1981) Proc. Natl. Acad. Sci. USA 78, 274-278 2. Casey, J.L., & Sauer, K. (1984) Biochim. Biophys. Acta 767, 21-28. 3. Zimmermann, J.L., & Rutherford, A.W. (1984) Biochim. Biophys. Acta 767, 160-167. 4. Petrouleas, V. and Diner, B.A. (1990) Biochim. Biophys. Acta 1015, 131-140. 5. Sanakis, Y., Goussias, Ch., Mason, R.P., Petrouleas, V. (1997) Biochemistry, in press.
G14
MANGANESE
207
LOW TEMPERATURE INTERACTIONS OF NO WITH THE Sl AND Sz STATES OF THE WATER OXIDISING COMPLEX OF PHOTOSYSTEM II. A NOVEL MN-MULTILINE EPR SIGNAL DERIVED FROM THE S1 STATE.
Charilaos Goussias, Nikolaos Ioannidis, and Vasili Petrouleas Institute of Materials Science, NCSR "'Democritos ", 15310 Aghia ParaskevLAthens, Greece The active site of the water oxidising complex of Photosystem II (PSII) is thought to be a cluster of four manganese atoms. During sequential absorption of photons by PSII the water oxidising complex undergoes four one-electron oxidation steps, S0-S~,..,$3-$4, coupled to the release of molecular oxygen. PSII centers after a period of dark adaptation relax in the majority to the SI state. It is generally agreed that this is an integer spin state. Single electron oxidation of $1 produces the half-integer-spin $2 state, which is EPR active and gives a characteristic multiline signal at 1.He temperatures [ 1] and under certain conditions an alternative signal at g=4.1 [2,3]. These signals and variants of them have been valuable in assaying and understanding basic features of the complex. In earlier studies it was shown that NO binds reversibly to the PSII acceptor side non-heme Fe 2+ producing a characteristic EPR signal at g=4, and also to tyr YD" producing an EPR silent species [4]. The latter interaction, which is fast and reversible, is slowly succeeded by the formation of a nitrosotyrosine complex [5]. This acts as a donor to PSII and can be oxidised by light to an iminoxyl radical. I an extension of these studies we have noted that N O interacts rapidly with the $2 state of the water oxidising complex at temperatures as low as -75 °C, to yield an EPR silent state. NO also interacts with the dark-stable S~ state but at a much lower rate. At -30 °C and in the presence of approx. 0.5 - 0.7 mM N O S~ loses the ability to yield by illumination an EPR active $2 state with an approximate half-time of 40-60 min. At longer incubation times (tl/2 4-5 h) an intense new multiline signal develops. The new signal has a hyperfine splitting similar to the S2-multiline but is characterised by intense lines on the high field side. The N O modified Si state can act as a low temperature electron donor yielding an EPR silent state upon illumination at 200 K. The new multiline signal is attributed to binding and magnetic interaction of N O with Sl to produce a half integer spin state with a S--1/2 ground state. The unusual reactivity of the Mn cluster with NO, which implies at least two binding sites of N O is correlated with the chloride site and the binding of ammonia, and by extension, with substrate binding. 1. Dismukes, G.C., & Siderer, Y. (1981) Proc. Natl. Acad. Sci. USA 78, 274-278 2. Casey, J.L., & Sauer, K. (1984) Biochim. Biophys. Acta 767, 21-28. 3. Zimmermann, J.L., & Rutherford, A.W. (1984) Biochim. Biophys. Acta 767, 160-167. 4. Petrouleas, V. and Diner, B.A. (1990) Biochim. Biophys. Acta 1015, 131-140. 5. Sanakis, Y., Goussias, Ch., Mason, R.P., Petrouleas, V. (1997) Biochemistry, in press.