Investigation of Rhodobacter Sphaeroides Reaction Center Mutants with Changed Ligands to the Primary Donor

The interaction of the primary donor (P), a dimer of bacteriochlorophylls (BChls), denoted PL and PM, with the protein environment in reaction centers (RCs) of Rhodobacter (Rb.) sphaeroides is studied in a series of mutants, in which His M202 is exchanged to either Glu, Asn, Ser, as well as in HL(M202) [1] and HG(M202) [2]. Mutant RCs were isolated and investigated by optical spectroscopy, redox titrations of P and EPR/ENDOR spectroscopy of the light-induced radical cation P*+. The aim of this study is to assess the ability of different amino acid residues to serve as axial ligand to PM and to influence the pigment composition of the RCs.