Control of composition and activity of the photosynthetic apparatus of Rhodopseudomonas capsulata grown in ammonium-limited continuous culture

Comparative studies of two membrane fractions isolated from chemotrophically and phototrophically grown cells of Rhodopseudomonas capsulata

Light and heavy membrane fractions have been isolated by equilibrium sucrose density centrifugation from Rhodopseudomonas capsulata 938 GCM grown aerobically in the dark (chemotrophically) and anaerobically in the light (phototrophically). The densities of the light and heavy fractions from phototrophic cells were 1.1004 to 1.1006 and 1.1478, respectively, and the densities of the light and heavy fractions from chemotrophic cells were 1.0957 to 1.0958 and 1.1315, respectively. Both fractions were active in photochemical and respiratory functions and in electron transport-coupled phosphorylation. The light membrane fraction isolated from chemotrophic cells contained the reaction center and the light-harvesting pigment-protein complex B 870, but not the variable light-harvesting complex B 800-850. A small amount of the complex B 800-850 was present in the light fraction isolated from phototrophically grown cells, but it was not energetically coupled to the photosynthetic apparatus. From inhibitor studies, difference spectroscopy, and measurement of enzyme activities it was tentatively concluded that the light membrane fraction contains only the reduced nicotinamide adenine dinucleotide-oxidizing electron transport chain having a KCN-insensitive, low-potential cytochrome c oxidase, whereas the heavy fraction contains additionally the succinate dehydrogenase and a high-potential cytochrome b terminal oxidase sensitive to KCN. The light membrane fraction was more labile than the heavy fraction in terms of phosphorylating activity.

Isolation and characterization of the polypeptide components from light-harvesting pigment-protein complex B800--850 of Rhodopseudomonas capsulata

The light-harvesting bacteriochlorophyll-carotenoid-protein complex B800--850 has been isolated from membranes of the phototroph-negative mutant strain Y5 of Rhodopseudomonas capsulata. The three polypeptides of the complex have been found to be soluble in chloroform-methanol (1:1, v/v) in the presence of 0.1 M ammonium acetate. They were extracted from the complex and separated by gel filtration on Sephadex LH-60 in the same solvent mixture. Minimum molecular weights based on amino acid composition are 12 000, 9300, and 5100. Values previously determined by sodium dodecyl sulfate/polyacrylamide gel electrophoresis are 14 000, 10 000 and 8000. The two smaller polypeptides (polarities 31% and 39%) are completely soluble in chloroform/methanol/ammonium acetate while the largest and most polar (41%) polypeptide is only partially soluble. The largest polypeptide contains no tryptophan. The middle polypeptide contains no cysteine and arginine, while the small polypeptide lacks cysteine. Methionine is shown to be the amino terminus for the small and middle polypeptides by two independent methods (Edman degradation and dansylation). Both methods also indicated that the N terminus of the 14 000 polypeptide seems to be blocked. Partial N-terminal amino acid sequences were obtained for the two smaller polypeptides. No homology between the two proteins was observed.

Effects of light intensity on membrane differentiation in Rhodopseudomonas capsulata

Cells of Rhodopseudomonas capsulata, strain 37b4, leu-, precultivated anaerobically under low light intensity, were exposed to high light intensity (2000 W.m-2). The cells grew with a mass doubling time of 3 h. The synthesis of bacteriochlorophyll (BChl) began after two doublings of cell mass. Reaction center and light-harvesting BChl I (B-875) were the main constituents of the photosynthetic apparatus incorporated into the membrane. The size of the photosynthetic unit (total BChl/reaction center) decreased and light-harvesting BChl I became the dominating BChl species. Concomitant with the appearance of the different spectral forms of BChl the respective proteins were incorporated into the membrane, i.e. the three reaction center polypeptides, the polypeptide associated with light-harvesting BChl I, the two polypeptides associated with BChl II. A polypeptide of an apparent molecular weight of 45 000 was also incorporated. A lowering of the light intensity to 7 W.m-2 resulted in a lag phase of growth for 6 h. Afterwards, the time for doubling of cell mass was 11 h. The concentration of all three BChl complexes (reaction center, light-harvesting BChl I and II complexes)/cell and per membrane protein increased immediately. Also the size of the photosynthetic unit and the amount of intracytoplasmic membranes/cell increased. The activities of photophosphorylation, succinate dehydrogenase, NADH dehydrogenase and NADH oxidation (respiratory chain)/membrane protein are higher in membrane preparations isolated from cells grown at high light intensities than in such preparations from cells grown at low light intensities.

Response of Rhodopseudomonas capsulata to illumination and growth rate in a light-limited continuous culture

Rhodopseudomonas capsulata was grown under anaerobic, photosynthetic conditions in a continuous culture device. Under light limitation, at a constant dilution rate, it was shown that cell composition, including photopigment (bacteriochlorophyll and carotenoids) and ribonucleic acid content, was not affected by incident light intensity; however, steady state culture density varied directly and linearly with light intensity. On the other hand, photopigment and ribonucleic acid levels were affected by growth rate regardless of light intensity. Additional experiments indicated a high apparent Ks for growth of R. capsulata with respect to light. These results were interpreted to mean that near the maximum growth rate (D = 0.45 h-1) some internal metabolic process became the limiting factor for growth, rather than the imposed energy limitation. A mathematical expression for the relation between steady-state culture density and dilution rate was derived and was found to adequately describe the data. A strong correlation was found between continuous cultures limited either by light or by a chemical energy source.

Isolation and characterization of light harvesting bacteriochlorophyll.protein complexes from Rhodopseudomonas capsulata

The isolation of two native light harvesting bacteriochlorophyl.protein complexes from Rhodopseudomonas capsulata is described. The light harvesting bacteriochlorophyll I (B 875) has been isolated from the blue-green mutant A1a+ lacking both carotenoids and light harvesting bacteriochlorophyll II. Light harvesting bacteriochlorophyll I is associated with a protein (light harvesting band 2) of 12 000 molecular weight. Light harvesting bacteriochlorophyll II complex has been isolated from the mutant Y5 lacking a reaction center and light harvesting bacteriochlorophyll I. Light harvesting bacteriochlorphyll II (B 800 + 850) together with carotenoids is associated with two polypeptides (light harvesting bands 3 and 4) having molecular weights of about 8000 and 10 000 (sodium dodecyl sulfate polyacrylamide gel electrophoresis). A third protein (light harvesting band 1) is in the purified light harvesting II fraction (mol. wt. approx. 14 000), but not associated with bacteriochlorophyll or carotenoids. The amino acid composition of the 3 antenna pigment II proteins is given. The polarity of these proteins was found to be 48%. From the amino acid composition the following molecular weights were calculated band 1: 17 350, band 3: 13 350 and band 4: 10 500.

Differentiation of the intracytoplasmic membrane of Rhodopseudomonas palustris induced by variations of oxygen partial pressure or light intensity

The photosynthetic apparatus of Rhodopseudomonas palustris contains, in addition to reaction center bacteriochlorophyll (Bchl) two spectral forms of light harvesting (LH) Bchl, i.e. LH Bchl I, characterized by an infrared absorption maximum at 880 nm (890 nm at 77 degrees K) and LH Bchl II absorbing at 805 and 855 nm (805 and 870 nm at 77 degrees K). LH Bchl I seems to be associated with a single protein species of an apparent mol. wt. of 13 000 whereas LH Bchl II is apparently associated with two proteins of mol. wts. of 9000 and 11 000. Cells in anaerobic cultures adapt to changes of light intensity 1. by variation of the size of the photosynthetic unit, i.e. the molar ratio of LH Bchl II to reaction center Bchl, 2. by variation of the number of photosynthetic units per unit of membrane area, 3. by regulation of the size of the intracytoplasmic membrane system. During adaptation of changes of oxygen partial pressure cells are able to synthesize reaction center Bchl, LH Bchl and intracytoplasmic membranes at different rates. The synthesis of reaction center Bchl and LH Bchl I are, however, coordinated with each other, while the synthesis of LH Bchl II and reaction center Bchl proceed independently.