Directionality of electron transfer within Photosystem I complex
Date
2001
Authors
Tang, Huadong
Major Professor
Advisor
Chitnis, Parag R.
Committee Member
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Abstract
PS I complex contains two branches of electron transfer chains. The question of the directionality of the electron transfer pathway remains unclear due to the symmetry of the two branches of electron transfer cofactors and the different experimental evidences. In this work, we addressed this question by introducing spin-labels in the vicinity of the phylloquinone in the A1 sites in photosystem I. Six residues in the PsaA and PsaB proteins were mutated to cysteinyl residues. Biochemical and biophysical characterizations were performed with mutant membranes and PS I complexes. Labeling of these residues with maleimide mediated biotin indicated the accessibility of introduced cysteines to the spin labeling. Purified PS I complexes were labeled with methanethiosulfonate nitroxide that introduced a spin group at the chemically modified cysteinyl residue. X-band EPR studies showed that the spin group was attached to the cysteinyl residues. The transient EPR experiments are being carried out to study the dipolar interactions between the A1 radical and attached spin group.
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thesis