Function of membrane proteins coupled to bacteriochlorophyll synthesis. Studies with wild type and mutant strains of Rhodopseudomonas spheroides

The photoreaction center of Rhodospirillum rubrum mutant strain F24.1

Rhodospirillum rubrum strain F24.1 is a spontaneous revertant of nonphototrophic mutant F24 derived from wild-type strain S1. Strain F24 shows no detectable photochemical activity and contains, at most, traces of the photoreaction center polypeptides. Strain F24.1 has a phototrophic growth rate close to that of the wild-type strain (Picorel, R., del Valle-Tascón, S. and Ramírez, J.M. (1977) Arch. Biophys. Biochem. 181, 665-670) but shows little photochemical activity. Light-induced absorbance changes in the near-infrared, photoinduced EPR signals and ferricyanide-elicited absorbance changes indicate that strain F24.1 has a photoreaction center content of 7-8% as compared to strain S1. Polyacrylamide gel electrophoresis of isolated F24.1 chromatophores shows the photoreaction center polypeptides to be present in amounts compatible with this value. Photoreaction center was prepared from strain F24.1 and showed no detectable difference with that of strain S1. It is concluded that strain F24.1 photosynthesis is due entirely to its residual 7-8% of typical photoreaction center.

Localization of photosynthetic membrane components in Rhodopseudomonas sphaeroides by a radioactive labeling procedure

Reduction with [3H]KBH4 of Schiff's bases generated by reaction with pyridoxal 5'-phosphate (which cannot penetrate the intact cytoplasmic membrane) yields tritium-labeled derivatives of both proteins and lipids accessible on the periplasmic side of the cytoplasmic membrane. Application of this technique to phototrophically grown Rhodopseudomonas sphaeroides labeled both the cell envelope and chromatophore fractions. The technique was also applied to R. sphaeroides harvested at various times during an adaptation from heterotrophic to phototrophic growth conditions. The specific activity of the chromatophore fraction after 20 h of adaptation was 76% of that found at the beginning, indicating that the intracytoplasmic membranes and cytoplasmic membrane form a continuous membrane system, with the majority of the intracytoplasmic membranes accessible to the external medium throughout the adaptation. The identity of the proteins labeled by this technique was investigated in two fractions labeled after cell disruption: normal "inside-out" chromatophores and "right-side-out" membrane vesicles isolated by lysozyme--osmotic shock treatment of cells grown in high light intensity (15000 lx). The results after sodium dodecyl sulfate--polyacrylamide gel electrophoresis and fluorography indicated that the 28000-dalton subunit (and to a lesser extent the 21000-dalton subunit) of the reaction center complex and two polypeptides in the light-harvesting region of the gel were heavily labeled in the chromatophores and were thus accessible on the cytoplasmic side of the membrane. At least one of the latter two polypeptides was also labeled in the membrane vesicles and was thus also accessible on the periplasmic side of the membrane. None of the reaction center subunits was significantly labeled in a reaction center complex prepared from the membrane vesicle sample.

A comparison of the constituent polypeptides of the B-800--850 light-harvesting pigment-protein complex from Rhodopseudomonas sphaeroides

The polypeptide composition of the B-800-850 light-harvesting pigment-protein complex from Rhodopseudomonas sphaeroides has been determined. The complex consists of equimolar amounts of two small polypeptides. The two polypeptides have very similar molecular weights and amino acid composition but are clearly separable by eithr SDS polyacrylamide gradient gel electrophoresis or isoelectric focussing.

Modifiable chromatophore proteins in photosynthetic bacteria

The chromatophores of Chromatium vinosum, as well as six other photosynthetic bacteria, contained two or more proteins which were insoluble when heated in the presence of sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (beta-ME). When the chromatophores were dissolved at room temperature in SDS-beta-ME, these proteins were present in the SDS-polyacrylamide gel electrophoresis profiles, but when the samples were dissolved at 100 degrees C, they were absent or considerably diminished. When one-dimensional gels of chromatophores solubilized at room temperature were soaked in the SDS-beta-ME solution and heated to 100 degrees C and the gels were run in a second dimension, the proteins became immobilized in the original first-dimension gel, where they could be detected by staining. The two major proteins so affected in C. vinosum had apparent molecular weights of 28,000 and 21,000. The chromatophores of several other photosynthetic bacteria also contained predominant proteins between 30,000 and 19,000 molecular weight, which became insoluble when heated in the presence of SDS and beta-ME. In at least two of the species examined, these appeared to be reaction center proteins. The conditions causing the proteins to become insoluble were complex and involved temperature, SDS concentration, and the presence of sulfhydryl reagents. The chromatophores of four of the Chromatiaceae species and two strains of one of the Rhodospirillaceae species examined had a protein-pigment complex that was visible in SDS-polyacrylamide gel profiles of samples dissolved at room temperature but was absent in samples dissolved at 100 degrees C.

Effect of heat and 2-mercaptoethanol on intracytoplasmic membrane polypeptides of Rhodopseudomonas sphaeroides

Solubilization at 75 degrees C of Rhodopseudomonas sphaeroides chromatophores in the presence of sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (beta-ME) resulted in the selective absence of reaction center B and C polypeptides from SDS-polyacrylamide gel electrophoresis profiles. A newly identified, chromatophore-specific polypeptide, with a mass of 35.2 kdaltons, was also missing under these conditions of chromatophore solubilization. Solubilization at 27 degrees C in the presence of SDS and beta-ME also resulted in the disappearance of these three polypeptides, but at much slower rates. Disappearance of either endogenous or exogenously supplied reaction center polypeptides B and C during SDS solubilization of whole chromatophores at either 27 or 75 degrees C was shown to be entirely dependent upon the presence of beta-ME. After chromatophore solubilization in the presence of beta-ME and subsequent SDS-polyacrylamide gel electrophoresis, exogenously added reaction centers B and C could be localized in a complex of no less than 100 to 200 kdaltons. However, the precise size of the complex was influenced by the stoichiometry of the reacting components. The disappearance of the 35.2-kdalton polypeptide was neither dependent upon the presence of beta-ME nor dependent upon the presence of any additional chromatophore polypeptides. The 35.2-kdalton polypeptide underwent a heat-induced oligomerization to yield several high-molecular-weight species.

The use of the fluorescent probe alpha-parinaric acid to determine the physical state of the intracytoplasmic membranes of the photosynthetic bacterium, Rhodopseudomonas sphaeroides

alpha-Parinaric acid has been used to determine the degree of ordering of the hydrocarbon region of purified intracytoplasmic membranes of Rhodopseudomonas sphaeroides. The usefulness of alpha-parinaric acid as a probe of membrane fluidity was established by comparison of its fluorescent properties in phosphatidylcholine vesicles with those of the more commonly used fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene. Both fluorescent probes were shown to monitor similar environments in the phosphatidylcholine vesicles when the phospholipids were maintained at temperatures above their phase transition temperature. The rotational mobility of alpha-parinaric acid in the intracytoplasmic membranes was determined from 0 to 50 degrees C, a region where no phase transitions were detectable. The rotational mobility of alpha-parinaric acid dissolved in vesicles formed from total extracted intracytoplasmic membrane phospholipids, was 2--3-fold greater than that measured in the intact intracytoplasmic membranes; demonstrating that the presence of protein greatly reduces the mobility of the phospholipid acyl chains of the intracytoplasmic membranes. Due to the high protein content of these membranes, the perturbing effect of protein on acyl chain mobility may extend to virtually all the intracytoplasmic membrane phospholipid.

Membrane-bound, pyridine nucleotide-independent L-lactate dehydrogenase of Rhodopseudomonas sphaeroides

Rhodopseudomonas sphaeroides has a pyridine nucleotide-independent L-lactate dehydrogenase associated with the membrane fraction of cells grown either aerobically or phototrophically. The dehydrogenase is present in cells grown on a variety of carbon sources, but at levels less than 20% of that found in cells grown with DL-lactate. The dehydrogenase has been purified 45-fold from membranes of strain L-57, a non-photosynthetic mutant, by steps involving solubilization with lauryl dimethylamine oxide and three anion-exchange chromatography steps. The purified enzyme was specific for the L-isomer of lactate. The Km of the purified enzyme for L-lactate is 1.4 mM, whereas that of the membrane-associated enzyme is 0.5 mM. The enzyme activity was inhibited competitively by D-lactate and non-competitively by oxalate and oxamate. Quinacrine, a flavin analog, also inhibited the activity. The inducible enzyme may serve as a marker of membrane protein in studies of membrane development.

Effects of incident light levels on photosynthetic membrane polypeptide composition and assembly in Rhodopseudomonas sphaeroides

Cells of Rhodopseudomonas sphaeroides were grown anaerobically with incident light levels ranging between 4,500 and 400 footcandles (ca. 48,420 and 4,304 lux). Cells grown with the higher light levels had lower contents of total bacteriochlorophyll and incorporated L-[U-14C]leucine into membrane protein at higher rates than cells grown with lower light levels. The former cells also contained relatively lower amounts of light-harvesting membrane polypeptides as compared with the latter cells. In contrast, the relative amounts of reaction center membrane polypeptides were approximately the same with varying incident light levels. The relative amounts of these membrane polypeptides were correlated with differences in rates of synthesis and assembly of the polypeptides into membrane by measuring the rates of incorporation of L-[U-14C]leucine into the membrane-bound polypeptides. No significant differences in rates of turnover of these polypeptides were detected under the varying incident light levels as measured in pulse-chase radioactive labeling experiments.

Membranes of Rhodopseudomonas sphaeroides. IV. Assembly of chromatophores in low-aeration cell suspensions

Chromatophore membrane formation was induced in low-aeration suspensions of Rhodopseudomonas sphaeroides and highly purified chromatophore preparations were isolated at various intervals between 4 and 18 h. The levels of several functional components associated with the isolated strucures were investigated. B-875, the light-harvesting bacteriochlorophyll complex associated with the reaction center, was preferentially inserted into the chromatophore membrane during the early stages of induction, and thereafter its levels reached a steady state; b- and c-type cytochromes were also maintained at essentially constant levels. In contrast, the levels of B-850, the accessory light-harvesting bacteriochlorophyll, together with its associated protein, continued to increase throughout the induction process. Increases in the levels of the major carotenoid component followed a similar course. These findings are consistent with a stepwise assembly mechanism for associated bacteriochlorophyll and protein components and suggest that separate regulatory mechanisms control the levels of functionally essential and accessory components within the membrane.

Formation of reaction centers and light-harvesting bacteriochlorophyll-protein complexes in Rhodopseudomonas capsulata

Formation of the photosynthetic apparatus was induced in aerobically grown dark cultures of Rhodopseudomonas capsulata by lowering of the oxygen tension. Besides the wild type strain the carotenoid-less mutant strain A1a+ was investigated. Both strains exhibited initially a decrease of the molar ratio of total bacteriochlorophyll (Bchl) to reaction center (RC) Bchl, followed by an increase. Synthesis of RC-Bchl preceded the synthesis of light-harvesting (LH) Bchl. Activities of photophosphorylation in membrane preparations, isolated from cultures after different periods of incubation at low aeration, decreased on the basis of total Bchl from about 9 to 2 mumole ATP/mumole total Bchl-min, whereas the rate on the basis of RC-Bchl remained constant (about 500 mumole ATP/mumole RC-Bchl-min). Under the same conditions the membrane proteins were labelled with U-14C-protein hydrolysate. Corresponding to RC-Bchl the synthesis of RC-proteins dominated during the first 30 min of incubation at PO2 below 3 mm Hg. After 45-60 min of membrane formation at low aeration the synthesis of LH-complex proteins exceeded the synthesis of RC proteins. The correlations between protein and Bchl synthesis in the sequential formation of RC- and LH-complexes are discussed.