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 · Wed Oct 18 00:00:00 EDT 1995 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja00146a017· OSTI ID:136297

Tommos, C ^[1]; Tang, X S; Diner, B A ^[2]; Warncke, K; Hoganson, C W; McCracken, J; Babcock, G T ^[3]; Styring, S ^[1]

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1. Stockholm Univ. (Sweden)
2. E. I. Du Pont deNemours and Co., Wilmington, DE (United States)
3. 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, Vol. 117, Issue 41; Other Information: PBD: 18 Oct 1995
• Country of Publication: United States
• Language: English

Related Subjects

55 BIOLOGY AND MEDICINE
BASIC STUDIES
40 CHEMISTRY
66 PHYSICS
OXYGEN
PHOTOSYNTHESIS
TYROSINE
REDOX REACTIONS
ENERGY SPECTRA
COMPLEXES
HYDROGEN
PHOTOSYNTHETIC REACTION CENTERS
CHEMICAL BONDS
OXIDATION
ENDOR
ELECTRON SPIN RESONANCE
ELECTRONIC STRUCTURE