Intracellular location of enzymes in rhodopseudomonas spheroides

Adaptation of Rhodopseudomonas spheroides

The composition of Rhodopseudomonas spheroides grown under oxygen or under air in the dark, or semi-anaerobically in the light was studied. The amounts of various constituents were expressed per cell. Anaerobically grown cells were 20 % lighter than cells grown under oxygen but contained approximately 50 % more protein and 85 % more phospholipid. The differences in weight were largely due to greater amounts of reserve material (poly-B-hydroxybutyrate and carbohydrate) in oxygen-grown cells. The major increase in the protein was due to a doubling of the 4particulate5 protein, the ‘soluble’ protein increasing by only 20% . The values of certain constituents in cells grown in air were intermediate between those of oxygen-grown cells and semi-anaerobically grown cells. The changes in composition were followed during adaptation from growth under oxygen to semi-anaerobic conditions in the light. Particulate protein, phospholipid, and enzymes concerned in bacteriochlorophyll synthesis increased markedly before photopigments or chromatophores were formed. These results indicate the sequence of some of the steps concerned in the differentiation of the cytoplasmic membrane of pigment-free microorganisms into the fully formed photosynthetic apparatus.

Distribution and metabolism of ornithine in Rhodopseudomonas spheroides

Ornithine lipid was found in chromatophores, in poorly pigmented subcellular fractions from pigmented micro-organisms and in fragments from cells grown under oxygen which have no bacteriochlorophyll. Its quantitative distribution among these different subcellular fractions did not correlate with the distribution of diaminopimelic acid. It is concluded that ornithine lipid is a specific constituent of the cytoplasmic membrane as opposed to the cell wall. Calculations indicate that about 20% of the ornithine lipid in pigmented cells is not associated with chromatophores. The cytoplasmic membrane content of unpigmented cells, calculated on the basis of ornithine lipid as a marker, was 15 to 22% of the total cell protein. Radioactivity from DL-[5- 14 C] ornithine in trace amounts was rapidly incorporated into growing cells. Most of the counts were in proline, arginine and glutamic acid residues of the proteins. However, nearly all the radioactivity incorporated into lipid was still present as ornithine. [5- 14 C]Ornithine incorporated into lipid of oxygen-grown cells did not turn over when the organisms were allowed to adapt to photosynthetic conditions but the lipid from the chromatophores was radioactive. During this adaptation the content of ornithine lipid per cell doubled with respect to the phospholipid, which increased twofold. The time course of these changes was parallel to that of bacteriochlorophyll synthesis. The significance of all these results in relation to the nature and biogenesis of the chromato­phores is discussed. It is pointed out also that studies on the distribution of ornithine lipid in other bacterial species may be of taxonomic importance.

Metabolic turnover of the lipids of Rhodopseudomonas spheroides

Experiments with L-[Me- 14 C]methionine and inorganic 32 P indicate that the lipids of this micro-organism are metabolically stable. Lipids of unpigmented cells were incorporated into chromatophores when these cells were allowed to adapt to semi-anaerobic conditions in the light. The specific radioactivity of the phospholipid of the chromatophores was the same as that of the adapted cells; thus it appears that no distinction can be made between different parts of the cytoplasmic membrane system with respect to the labelling of the lipids. It is concluded that chromatophores originate from the cytoplasmic membrane and remain structurally a part of it.