Some Factors Influencing the Shape of the Near-infrared Absorption Spectrum of Chromatium, Strain D

During a considerable period of time, several investigators have been engaged in the problem of the multi-peak character of the absorption spectra of purple bacteria. In Athiorhodaceae mainly two, and in Thiorhodaceae mainly three absorption maxima exist (1, 2). Different suggestions were made to explain the existence of several peaks in the in vivo spectra of purple bacteria, since only one bacteriochlorophyll maximum was found in organic extracts. Pigments, active in light absorption in photosynthesis all seem to be closely related to proteins (3, 4). Some reasons to believe in this relation may be mentioned, viz., 1. Suspensions, containing the chlorophyll or bacteriochlorophyll pigments may be obtained artificially, e.g., by ultrasonic disintegration of cells, by thorough grinding of cells and subsequent aqueous extraction or with the aid of detergents. In aqueous suspensions, amphoteric motion in an electric field has been observed (1). 2. Purple bacteria (probably dead cells) sometimes show spontaneous extrusion of a bacteriochlorophyll and carotenoids containing pigment complex similar to that obtained by grinding the cells. 3. Practically all pigments known to play a part in photosynthesis show a shift of their absorption bands by extraction. As already remarked, in several strains of purple bacteria, bacteriochlorophyll in vivo has a complicated absorption spectrum in the near-infrared which differs with the species (1, 2). In organic solvents, however, bacteriochlorophyll, regardless of the species from which it has been extracted, shows only one absorption peak, the two or three original maxima have all shifted to the same