title: Probing the primary donor environment in the histidineM200-->leucine and histidineL173-->leucine heterodimer mutants of Rhodobacter capsulatus by light-induced Fourier transform infrared difference spectroscopy.
abstract: Light-induced P+QB-/PQB FTIR difference spectra of reaction centers (RCs) have been obtained from chromatophores lacking light-harvesting B800-850 antenna for Rhodobacter capsulatus wild type (WT) and for the two mutants HisM200-->Leu and HisL173-->Leu. The primary donor (P) in both mutants consists of a bacteriochlorophyll-bacteriopheophytin heterodimer. The most prominent difference between the WT and the mutant spectra is in the 1600-1200-cm-1 region. The WT spectrum displays large positive bands at approximately 1290, 1500-1430, and 1580-1530 cm-1. These three bands are either small or altogether absent in the heterodimer spectra. In addition, both heterodimer spectra compare well with the electrochemically generated BChla+/BChla spectrum [Mäntele, W.G., Wollenweber, A. M., Nabedryk, E., & Breton, J. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 8468-8472]. These observations indicate that the positive charge is localized on the monomeric BChl in the heterodimers. The overall shape of the ester and keto C = O signals in the BChla+/BChla spectrum is maintained in the in situ spectra although significant differences are observed in the frequency, width, and splitting of the bands. The shape of the signal at 1757/1744 cm-1 in HisL173-->Leu is comparable to the 1751/1737-cm-1 signal of BChla+/BChla in tetrahydrofuran, indicating a free 10a ester C = O of PM in HisL173-->Leu. The reduced amplitude of the negative 1740-cm-1 feature in both HisM200-->Leu and WT spectra suggests a hydrogen-bonded 10a ester C = O for PL.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Département de Biologie Cellulaire et Moléculaire, Centre d'Etudes Nucléaires de Saclay, Gif-sur-Yvette, France.
authors.forename: E
authors.initials: E
authors.lastname: Nabedryk
authors.forename: S J
authors.initials: SJ
authors.lastname: Robles
authors.forename: E
authors.initials: E
authors.lastname: Goldman
authors.forename: D C
authors.initials: DC
authors.lastname: Youvan
authors.forename: J
authors.initials: J
authors.lastname: Breton
mesh_terms: D001429:Bacteriochlorophylls / Q000737:chemistry; D004563:Electrochemistry; D006639:Histidine / Q000737:chemistry*; D007930:Leucine / Q000737:chemistry*; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D009154:Mutation; D010674:Pheophytins / Q000737:chemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics; D016354:Rhodobacter capsulatus / Q000737:chemistry* / Q000235:genetics; D013055:Spectrophotometry, Infrared
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; C006678:bacteriopheophytin; D006639:Histidine; D007930:Leucine