Absorption and structure of an LM unit isolated with sodium dodecyl sulfate from reaction centers of Rhodopseudomonas sphaeroides

Low-temperature absorption, circular dichroism and resonance Raman spectra of the LM units isolated with sodium dodecyl sulfate from wild-type Rhodopseudomonas sphaeroides reaction centers (Agalidis, I. and Reiss-Husson, F. (1983) Biochim. Biophys. Acta 724, 340–351) are described in comparison with those of intact reaction centers. In LM unit, the Q_y absorption band of P-870 at 77 K shifted from 890 nm (in reaction center) to 870 nm and was broadened by about 30%. In contrast, the 800 nm bacteriochlorophyll absorption band including the 810 species remained unmodified. It was concluded that the 810 nm transition is not the higher excitonic component of P-870. The Q_x band of P-870 shifted from 602 nm (in reaction center) to 598 nm in LM, whereas the Q_x band of the other bacteriochlorophylls was the same in reaction center and LM and had two components at about 605 and 598 nm. The Q_xII band of bacteriopheophytin was upshifted to 538 nm and a slight blue shift of the Q_y band of bacteriopheophytin was observed. Resonance Raman spectra of spheroidene in LM showed that its native cis-conformation was preserved. Resonance Raman spectroscopy also demonstrated that in LM the molecular interactions assumed by the conjugated carbonyls of bacteriochlorophyll molecules were altered, but not those assumed by the bacteriopheophytins carbonyls. In particular at least one Keto group of bacteriochlorophyll free in reaction center, becomes intermolecularly bounded in LM (possibly with extraneous water). This group may belong to the primary donor molecules.