C-13 MAGIC ANGLE SPINNING NMR EVIDENCE FOR A 15,15'-Z CONFIGURATION OF THE SPHEROIDENE CHROMOPHORE IN THE RHODOBACTER-SPHAEROIDES REACTION CENTER - SYNTHESIS OF C-13-LABELED AND H-2-LABELED SPHEROIDENES

The synthesis of the isotope-labelled spectroscopic probes [14'-C-13]-, [15'-C-13]-, [14'-H-2], [15'-H-2]-, [15-H-2]- and [14-H-2]-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) C-13 NMR spectroscopy on R-26 reaction centers reconstituted with [14'-C-13]-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 gamma-effect at C14, and provides evidence for a 15,15'-Z configuration of the chromophore in the active site.