PARENT SESSION

Symposium S5A Type II reaction centres: Structure
Wednesday September 1st, 2004 10:20 AM-12:20 PM Room 210A
Chair: Dave Britt
Co-Chair: Rick Debus

High frequency EPR of the Mn-cluster in single crystals of cyanobacterial photosystem II. Asako Kawamori¹, Jian-Ren Shen², Hiroyuki Mino^*,3, Kou Furukawa⁴, ¹ Kwansei Gakuin University, School of Science, Sanda, Hyogo, Japan² Okayama University Department of Biology, PRESTO JST Saitama, Okayama, Japan³ Nagoya University, Department of Physics, Nagoya, Aichi, Japan⁴ Institute of Molecular Science, Okazaki, Aichi, Japan

ABSTRACT- Mn EPR multiline signal of the S₂-state of single crystals of Thermosynechococcus vulcanus photosystem II (PSII) was observed at 6K by a W-band(94GHz) EPR spectrometer. The signal seemed to consist 21 lines, suggesting the contribution from four manganese atoms. The hyperfine splitting varied slightly depending on the crystal orientation relative to the magnetic field, while the intensities and positions of hyperfine lines changed significantly with different crystal orientations. No multiline signal was observed in the same PSII of frozen solution. The results were compared with the calculated values by assuming g-anisotropy derived by Peloquin et al. [1] for a model in which a trimer manganese was weakly coupled with fourth manganese atom. The orientations of g-tensors were determined, as shown in Table 1. Calculations for the direction cosine of hyper fine interaction (hfs) tensors are now underway. Similar spectra were observed in the S₀-state obtained by reduction of the crystal with hydroxyl amine. Further experimental evidence of the S₀-state will be achieved with flash induced and/or formate induced S₀ state, which should increase the population of the S₀state. The anisotropy obtained from high frequency EPR will provide the valence states of each manganese for each S-state by comparison with the crystal structure data.
Table 1 The values of g-components and their direction cosines
g_x = 1.9691, g_y = 1.9713, g_z = 1.9865

	x	y	z
a	0.2815	0.9590	0.0341
b	0.5577	-0.1924	0.8074
c	-0.7809	0.2083	0.5890

[1] Peloquin et al. (2000) J. Am. Chem. Soc. 122, 10926-10942

KEY WORDS: S2-state, g-anisotropy, Mn-cluster, W-band EPR