Energy Transfer and Cytochrome Function in a New Type of Photosynthetic Bacterium*

The excitation spectrum for bacteriochlorophyll b fluorescence at 1027 mp in Rhodopseudomas sp. NHTC 133 indicates that the efficiency of energy transfer from carotenoid to bacteriochlorophyll b is between 27 and 28 per cent. Light‐induced absorbancy changes in anaerobic whole cells indicated the oxidation of three c‐type cytochromes (C‐550.5, C‐553, C‐558) and one b‐type cytochrome or cytochromoid C (C‐560). At low light intensities C‐553 is the main cytochrome oxidized, while at high light intensities mainly C‐558 is oxidized in addition to C‐553. The light responses of the heme proteins appear to be similar to those observed previously in purple and green photosyn‐thetic bacteria. No light‐induced shifts in carotenoid absorption bands were detected. In bacterial extracts C‐553 and C‐558 are bound to the chromatophores, while C‐550.5 is soluble.