Spectroscopical studies on the light-harvesting pigment-protein complex II from dark-aerobic and light-anaerobic grown cells of Rhodobacter sulfidophilus

The photosynthetic bacterium Rhodobacter sulfidophilus can grow and synthesize photosynthetic pigments under dark-aerobic as well as light-anaerobic growth conditions. Under both growth conditions intracytoplasmic membrane vesicles (diameter about 35 nm) are formed. The light-harvesting (LH) pigment-protein complex II, isolated from dark-aerobic and light-anaerobic grown cells, consists of two small polypeptides (< 5 kDa) and the pigments bacteriochlorophyll and carotenoids. The carotenoid composition of the LHII complex, as shown by absorption spectroscopy in the 450 to 550 nm region, changed when the cells were transferred from aerobic-dark to anaerobic-light conditions. The absorption maxima in the near infrared regions varied reversibly depending on such factors as salt concentration and detergent. These shifts of absorption bands either reflect a change of tertiary structure of the polypeptides, which then modify pigment-pigment and/or reflect a direct influence of the ions onto the conjugated system of the pigments.