Intracellular location of enzymes in Rhodopseudomonas spheroides

Abstract

By differential centrifugation of extracts of pigmented R. spheroides, a number of constituents, phospholipid and lipid ornithine, and enzymes, zinc protoporphyrin chelatase, succinic dehydrogenase and S-adenosylmethionine-magnesium protoporphyrin methyltransferase, were found to be associated both with chromatophores and 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-were only 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. The cytoplasmic membrane, apart from lacking the photosynthetic pigments, has a composition similar to that of chromatophores. Electron microscopic studies indicate that chromatophores are probably derived by invagination of the cytoplasmic membrane.