Effects of hydrogen bonding and structure of the accessory bacteriochlorophylls on charge separation in Rb. capsulatus reaction centers

Histidine residues have been introduced into Rb. capsulatus reaction centers at M-polypeptide position 201 and at L-polypeptide position 174 to engender hydrogen bonds to the ring-V keto groups of the accessory bacteriochlorophyll cofactors B _A and B _B, respectively. Resonance Raman studies indicate that both mutations result in hydrogen-bonding interactions, as well as significant perturbations to the structure of the bacteriochlorophyll macrocycles. Nonetheless, ultrafast transient absorption measurements show that the structural/energetic effects of the mutations cause only minor changes in the primary photochemistry.