Site-directed mutations affecting the spectroscopic characteristics and midpoint potential of the primary donor in photosystem I

The effects of the helix X domain of the PsaB heterodimeric protein complex in the coordination of the reaction centers (RC) of the P700 chlorophyll a dimer were analyzed in genetically engineered H656 mutants of PsaB. The oxidation midpoint potential of P700/P700 + was increased to 40 microVolts in mutant His-656 PsaB RC proteins. The midpoint potential of P700 photosystem I was affected by hydrogen bond that was formed between the His-656 of PsaB RC protein and the carbonyl group of chlorophyll a in P700.