Spin-density distribution, conformation, and hydrogen bonding of the redox-active tyrosine Y{sub z} in photosystem II from multiple electron magnetic-resonance spectroscopies: Implications for photosynthetic oxygen evolution
Journal Article
·
· Journal of the American Chemical Society
- Stockholm Univ. (Sweden)
- E. I. Du Pont deNemours and Co., Wilmington, DE (United States)
- Michigan State Univ., East Lansing, MI (United States)
The oxidized form of the redox-active Y{sub Z} tyrosyl residue involved in photosynthetic oxygen evolution has been generated and trapped in Mn-depleted Photosystem II core complexes from a D2-Y160F mutant strain of Synechocystis 6803. This system eliminates interference from P{sub 700}{sup +} and Y{sub D}D+{center_dot} and allowed characterization of Y{sub Z}{sup {center_dot}} by using a combination of specific {sup 2}H-labeling and electron magnetic-resonance techniques that included CW-EPR, frequency-modulated and transient detected ENDOR, and {sup 2}H-ESEEM. Using these complementary techniques, we have carried out a detailed evaluation of the hyperfine structure of Y{sub Z}{sup {center_dot}} and obtained the dipolar interactions to weakly coupled nuclei, the strongly anisotropic tensors of the ring-hydrogens, and the more isotropic interactions to the {Beta}-methylene site. We conclude that tyrosyl radicals are not tuned to specific function by large-scale modulations of their spin density through hydrogen-bonding effects. We suggest a hydrogen-atom transfer function for Y{sub Z} in water oxidation. Within this model, the (Mn){sub 4}/Y{sub Z} center forms the Oxygen-Evolving Complex of Photosystem II where the (Mn){sub 4} cluster binds substrate water and delocalizes oxidizing equivalents and Y{sub Z} acts by abstracting hydrogens from substrate water in either a concerted or sequential fashion. 71 refs., 8 figs., 2 tabs.
- OSTI ID:
- 136297
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 41 Vol. 117; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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