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An antenna fraction designated B800/1020 according to its near-infrared absorption maxima has been isolated from the bacteriochlorophyll b -containing photosynthetic bacterium, Ectothiorhodospira halochloris . It contains five polypeptides (approx. 4.5, 6.0, 6.5, 15.5 and 35 kDa), at least five strongly interacting BChl b chromophores and no carotenoids. Energy is transferred from the chromophores absorbing around 800 nm to the ones absorbing at 1020 nm. The B800/1020 fraction as well as chromatophores, sphaeroplasts or whole bacteria are reversibly transformed with acid to form B800/960 with a p K value of approx. 6.3. Circular dichroism and low-temperature fluorescence data of the ‘low-pH form’ indicate only little structural rearrangement of the chromophores and a retention of the energy transfer.

Rhodospirillum rubrum and Rhodopseudomonas spheroides, grown under various degrees of illumination, aeration, and iron deprivation, have been assayed for their content of cytochrome c, RHP, catalase, total iron, bacteriochlorophyll, and carotenoids.