Identification of a hydrogen bond in the Phe M197 -> Tyr mutant reaction center of the photosynthetic purple bacterium Rhodobacter sphaeroides by X-ray crystallography and FTIR spectroscopy

In bacterial reaction centers the charge separation process across the phot osynthetic membrane is predominantly driven by the excited state of the bac teriochlorophyll dimer (D), An S-ray structure analysis of the Phe M197-->T yr mutant reaction center from Rhodobacter sphaeroides at 2.7 Angstrom reso lution suggests the formation of a hydrogen bond as postulated by Wachtveit l et al, Biochemistry 32, 12875-12886, 1993] between the Tyr M197 hydroxy g roup and one of the 2a-acetyl carbonyls of D, In combination with electroch emically induced FTIR difference spectra showing a split band of the pi-con jugated 9-keto carbonyl of D, there is clear evidence for the existence of such a hydrogen bond. (C) 1999 Federation of European Biochemical Societies .