TRIPLET-STATES IN REACTION-CENTER, LIGHT-HARVESTING COMPLEX B875 AND ITS SPECTRAL FORM B840 FROM RUBRIVIVAX-GELATINOSUS INVESTIGATED BY ABSORBENCY-DETECTED ELECTRON-SPIN-RESONANCE IN ZERO MAGNETIC-FIELD (ADMR)

Absorbance-detected magnetic resonance (ADMR) spectroscopy was used fo r characterization of the triplet states in several pigment-protein co mplexes from Rubrivivax gelatinosus, namely the isolated reaction cent er, the core light-harvesting complex B875, and the B875 subunit form that absorbs in the infrared at 820 nm (B820), and, in the presence of glycerol, at about 840 nm (B840). The zero-field splitting parameters of the triplet states were determined and T - S spectra were recorded at 1.2 K. The absorbance and T - S spectra of the reaction center res emble closely those of Rhodobacter sphaeroides, except for slight shif ts in the band positions. For the isolated B875 complex, only the trip let state of carotenoid was observed, indicating that triplet-triplet transfer from bacteriochlorophyll a to the carotenoid proceeds as in t he native system. The near-infrared absorption spectrum of B840 at 1.2 K revealed several overlapping bands, which were deconvoluted in five Gaussian components corresponding to free BChl a (795 nm), B820 (826 nm), small population of B875 (888 nm) and two new spectral forms B846 and B868, The origin of these two latter spectral forms is proposed t o reflect inaccurate reassociation of B820. Probably, oligomers of var ious sizes are formed, with different strengths of pigment-pigment and pigment-protein interactions. The T - S spectrum of B840 is consisten t with that of a BChl a dimer containing a localized triplet state.