A High-Field EPR Study of P700+ in Wild-Type and Mutant Photosystem I from Chlamydomonas reinhard
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- 作者：Alexander Petrenko ; Anna Lisa Maniero ; Johan van Tol ; Fraser MacMillan ; Yajing Li ; Louis-Claude Brunel ; and Kevin Redding
- 刊名：Biochemistry
- 出版年：2004
- 出版时间：February 24, 2004
- 年：2004
- 卷：43
- 期：7
- 页码：1781 - 1786
- 全文大小：154K
- 年卷期：v.43,no.7(February 24, 2004)
- ISSN：1520-4995
文摘
High-frequency, high-field EPR at 330 GHz was used to study the photo-oxidized primarydonor of photosystem I (P700+
) in wild-type and mutant forms of photosystem I in the green algaChlamydomonas reinhardtii. The main focus was the substitution of the axial ligand of the chlorophylla and chlorophyll a' molecules that form the P700 heterodimer. Specifically, we examined PsaA-H676Q,in which the histidine axial ligand of the A-side chlorophyll a' (PA) is replaced with glutamine, andPsaB-H656Q, with a similar replacement of the axial ligand of the B-side chlorophyll a (PB), as well asthe double mutant (PsaA-H676Q/PsaB-H656Q), in which both axial ligands were replaced. We alsoexamined the PsaA-T739A mutant, which replaces a threonine residue hydrogen-bonded to the 131-ketogroup of PA with an alanine residue. The principal g-tensor components of the P700+ radical determinedin these mutants and in wild-type photosystem I were compared with each other, with the monomericchlorophyll cation radical (Chlz+) in photosystem II, and with recent theoretical calculations for differentmodel structures of the chlorophyll a+ cation radical. In mutants with a modified PB axial ligand, the gzzcomponent of P700+ was shifted down by up to 2 × 10-4, while mutations near PA had no significanteffect. We discuss the shift of the gzz component in terms of a model with a highly asymmetric distributionof unpaired electron spin in the P700+ radical cation, mostly localized on PB, and a deviation of the PBchlorophyll structure from planarity due to the axial ligand.
) in wild-type and mutant forms of photosystem I in the green algaChlamydomonas reinhardtii. The main focus was the substitution of the axial ligand of the chlorophylla and chlorophyll a' molecules that form the P700 heterodimer. Specifically, we examined PsaA-H676Q,in which the histidine axial ligand of the A-side chlorophyll a' (PA) is replaced with glutamine, andPsaB-H656Q, with a similar replacement of the axial ligand of the B-side chlorophyll a (PB), as well asthe double mutant (PsaA-H676Q/PsaB-H656Q), in which both axial ligands were replaced. We alsoexamined the PsaA-T739A mutant, which replaces a threonine residue hydrogen-bonded to the 131-ketogroup of PA with an alanine residue. The principal g-tensor components of the P700+ radical determinedin these mutants and in wild-type photosystem I were compared with each other, with the monomericchlorophyll cation radical (Chlz+) in photosystem II, and with recent theoretical calculations for differentmodel structures of the chlorophyll a+ cation radical. In mutants with a modified PB axial ligand, the gzzcomponent of P700+ was shifted down by up to 2 × 10-4, while mutations near PA had no significanteffect. We discuss the shift of the gzz component in terms of a model with a highly asymmetric distributionof unpaired electron spin in the P700+ radical cation, mostly localized on PB, and a deviation of the PBchlorophyll structure from planarity due to the axial ligand.