Intracellular location of enzymes in Rhodopseudomonas spheroides

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Abstract
By differential centrifugation of extracts of pigmented Rhodopseudomonas spheroides a number of constituents, phospholipid and lipid ornithine, and enzymes, zinc protoporphyrin chelatase, succinic dehydrogenase and S-adenosylmethionine-magnesium protoporphyrin methyltransferase, have been found to be associated both with chromatophores and with non-pigmented particulate material. These components are present in both types of material at about the same level. In extracts of non-pigmented organisms the particulate material contains some of the above components, but others are only present in low amounts. The subcellular structures present in the particulate material—ribosomes, cell wall and cytoplasmic membrane—have only been partially separated but, by comparing the distribution of the components listed above with those of known components of ribosomes and cell wall, it is probable that they are associated with cytoplasmic membrane. These studies suggest that the cytoplasmic membrane, apart from lacking the photosynthetic pigments, has a composition similar to that of chromatophores. The data are consistent with the conclusion drawn from electron microscopic studies that chromatophores are derived by invagination of the cytoplasmic membrane.