13C Magic angle spinning nmr evidence for a 15,15’ -z configuration of the spheroidene chromophore in the rhodobacter sphaeroides reaction center; synthesis of 13c- and 2h-labelled spheroidenes

Abstract

The synthesis of the isotope-labelled spectroscopic probes [14’-13C]-, [15’-13C]-, [14’-2H], [15’-2H]-, [15-2H]- and [14-2H]-spheroidene, all with more than 98% enrichment, is described. In addition, the structure of the carotenoid in the photosynthetic reaction reaction center of Rhodobacter sphaeroides has been studied with solid state magic angle spinning (MAS) 13C NMR spectroscopy on R-26 reaction centers reconstituted with [14’-13C]-spheroidene. The isotope-label is found to resonate at 125.3 ppm, which is 6.6 ppm upfield from the resonance in all-E spheroidene. This indicates the presence of a y-effect at C14. and provides evidence for a 15,15’-Z configuration of the chromophore in the active site. © 1991 IUPAC