The isolation and characterization of subcellular fractions from pigmented and unpigmented cells of Rhodopseudomonas spheroides

Abstract

The nature and development of the chroma-tophores of photosynthetic bacteria are reviewed. A simple method of obtaining purified chromatophores by sucrose density gradient cen-trifuging of cell-free extracts of R. spheroides is described. Such preparations consist of about 60% protein, 20% phospholipid and 10% pigment, roost of which is bacteriochlorophyll. Small quantities of carbohydrate, but only traces of nucleic acid, are found. The material was fairly homogeneous on electron microscopy. The R. spheroides was also grown under pure O2 in the dark. A participate preparation from cells cultured under these conditions was similar to the chromatophores with respect to its high content of protein and phospholipid, much greater content of nucleic acid and no bacteriochlorophyll. It contained amino sugars and diaminopimelic acid not found in chromatophores. These differences in chemical composition were correlated with the electron microscope appearances of the different subcellular fractions. The particulate preparation from cells grown under O2 probably represents the cytoplasmic membrane, but it is heavily contaminated with fragments of the cell wall from which it cannot be readily separated.