The formation of bacteriochlorophyll.protein complexes of the photosynthetic apparatus of Rhodopseudomonas capsulata during early stages of development

The Small RNA-Binding Protein CcaF1 Promotes Formation of Photosynthetic Complexes in Rhodobacter sphaeroides

In natural habitats, bacteria frequently need to adapt to changing environmental conditions. Regulation of transcription plays an important role in this process. However, riboregulation also contributes substantially to adaptation. Riboregulation often acts at the level of mRNA stability, which is determined by sRNAs, RNases, and RNA-binding proteins. We previously identified the small RNA-binding protein CcaF1, which is involved in sRNA maturation and RNA turnover in Rhodobacter sphaeroides. Rhodobacter is a facultative phototroph that can perform aerobic and anaerobic respiration, fermentation, and anoxygenic photosynthesis. Oxygen concentration and light conditions decide the pathway for ATP production. Here, we show that CcaF1 promotes the formation of photosynthetic complexes by increasing levels of mRNAs for pigment synthesis and for some pigment-binding proteins. Levels of mRNAs for transcriptional regulators of photosynthesis genes are not affected by CcaF1. RIP-Seq analysis compares the binding of CcaF1 to RNAs during microaerobic and photosynthetic growth. The stability of the pufBA mRNA for proteins of the light-harvesting I complex is increased by CcaF1 during phototrophic growth but decreased during microaerobic growth. This research underlines the importance of RNA-binding proteins in adaptation to different environments and demonstrates that an RNA-binding protein can differentially affect its binding partners in dependence upon growth conditions.

Gene expression of pigment-binding proteins of the bacterial photosynthetic apparatus: Transcription and assembly in the membrane of Rhodopseudomonas capsulata

Lowering of oxygen partial pressure in chemotrophic cultures or reduction of light intensity in phototrophic cultures of Rhodopseudomonas capsulata induced formation of the photosynthetic apparatus. A maximum of mRNA coding for the reaction center (RC) and the light-harvesting 1 B870 antenna complex polypeptides occurred 30 min after induction. Maximal expression of mRNA for B800-B850 antenna proteins appeared with a lag time of about 25 min after RC/B870 mRNA. Pigment-binding polypeptides were inserted into the membrane immediately after mRNA synthesis. It is concluded that the delayed formation of the B800-B850 complex compared to the RC and the B870 complex is caused by sequential expression of the corresponding genes. Biological activity of pigment-protein complexes increased after the incorporation of their polypeptides parallel to the maximum of bacteriochlorophyll synthesis. Studies on mutant strains defective in the formation of pigment-protein complexes suggested that pigment synthesis is of importance for assembly of stable complexes.

Small RNA-induced differential degradation of the polycistronic mRNA iscRSUA

Most polycistronic genes are expressed in a single transcript, in which each cistron produces a fixed amount of protein. In this report, we show the first example of differential degradation of a polycistronic gene induced by a small regulatory RNA (sRNA). Our data show that the iron-responsive sRNA, RyhB, binds to the second cistron of the polycistronic mRNA, iscRSUA, which encodes the necessary machinery for biosynthesis of Fe-S clusters, and promotes the cleavage of the downstream iscSUA transcript. This cleavage gives rise to the remaining 5'-section of the transcript encoding IscR, a transcriptional regulator responsible for activation and repression of several genes depending on the cellular Fe-S level. Our data indicate that the iscR transcript is stable and that translation is active. The stability of the iscR transcript depends on a 111-nucleotide long non-translated RNA section located between iscR and iscS, which forms a strong repetitive extragenic palindromic secondary structure and may protect against ribonucleases degradation. This novel regulation shows how sRNAs and mRNA structures can work together to modulate the transcriptional response to a specific stress.

Sequential assembly of photosynthetic units in Rhodobacter sphaeroides as revealed by fast repetition rate analysis of variable bacteriochlorophyll a fluorescence

The development of functional photosynthetic units in Rhodobacter sphaeroides was followed by near infra-red fast repetition rate (IRFRR) fluorescence measurements that were correlated to absorption spectroscopy, electron microscopy and pigment analyses. To induce the formation of intracytoplasmic membranes (ICM) (greening), cells grown aerobically both in batch culture and in a carbon-limited chemostat were transferred to semiaerobic conditions. In both aerobic cultures, a low level of photosynthetic complexes was observed, which were composed of the reaction center and the LH1 core antenna. Interestingly, in the batch cultures the reaction centers were essentially inactive in forward electron transfer and exhibited low photochemical yields F(V)/F(M), whereas the chemostat culture displayed functional reaction centers with a rather rapid (1-2 ms) electron transfer turnover, as well as a high F(V)/F(M) of approximately 0.8. In both cases, the transfer to semiaerobiosis resulted in rapid induction of bacteriochlorophyll a synthesis that was reflected by both an increase in the number of LH1-reaction center and peripheral LH2 antenna complexes. These studies establish that photosynthetic units are assembled in a sequential manner, where the appearance of the LH1-reaction center cores is followed by the activation of functional electron transfer, and finally by the accumulation of the LH2 complexes.

Forty-five years of developmental biology of photosynthetic bacteria

Developmental biology and cell differentiation of photosynthetic prokaryotes are less noticed fields than the showpieces of eukaryotes, e.g. Drosophila melanogaster. The large metabolic versatility of the facultative purple bacteria and their great capability to adapt to different ecological conditions, however, aroused the inquisitiveness to investigate the process of cell differentiation and to use these bacteria as model system to study structure, function and biosynthesis of the photosynthetic apparatus. The great progress in research in this field paved the way to study principal mechanisms of cellular organization and differentiation in these bacteria. In this article, the history of the research on membrane structure and development of anoxygenic photosynthetic prokaryotes during the last 45 years is described. A personal account of how I entered the field through research on the phototaxis of cyanobacteria is given. Intracytoplasmic membranes (ICM) were detected by electron microscopy in cyanobacteria and in purple non-sulfur bacteria. The formation of ICM by invagination of the cytoplasmic membrane in purple bacteria was observed for the first time. Investigations on the effect of changes in oxygen tension and light intensity on the formation of pigments and intracytoplasmic membranes followed. The isolation, purification, and analysis of light-harvesting complexes and of pigment-binding proteins was the next step of our research. Lipopolysaccharides and peptidoglycans were detected and analyzed in the outer membrane of photosynthetic bacteria. Functional membrane differentiation includes variations in the rates of photophosphorylation and electron transport. Molecular genetic approaches have initiated the investigation of transcriptional regulation and the analysis of correlation between pigment and protein synthesis. Molecular analysis of assembly of light-harvesting complexes and membrane differentiation are the present aspects of our research. Cell differentiation has been considered under evolutionary view.

Cloning of a new antenna gene cluster and expression analysis of the antenna gene family of Rhodopseudomonas palustris

The genome of Rhodopseudomonas palustris contains five antenna gene clusters, alpha beta a, alpha beta b, alpha beta c, alpha beta d and alpha beta e, which encode the light-harvesting peripheral antenna complex II polypeptides. The isolation and characterisation of the gene which encodes the alpha e and beta e polypeptides are reported. The primary structure of the beta e polypeptide is identical to that of beta b whilst the structure of alpha e is different from the other alpha subunits so far characterised. All five of the gene clusters were transcribed under high-light conditions while under low-light conditions only three were transcribed (alpha beta b, alpha beta d and alpha beta e). Furthermore, Northern-blot analysis showed that the gene clusters encode RNA transcripts of either 500 or 650 nucleotides. Individual members of the gene family showed a differential response in terms of the regulation of abundance of mRNA upon growth under either high-light or low-light intensities. Possible promoter sequences and operator sites upstream of the alpha beta b, alpha beta d and alpha beta e genes were located. Furthermore using puc-lacZ fusions in trans in R. palustris, we were able to examine the positions of the promoter of the gene clusters. The significance of these observations with respect to the regulation, organization and role of the peripheral antenna is discussed.

Organization of the genes coding for the reaction-centre L and M subunits and B870 antenna polypeptides alpha and beta from the aerobic photosynthetic bacterium Erythrobacter species OCH114

In the aerobic photosynthetic bacterium Erythrobacter species OCH114 the structural genes coding for the light-harvesting (LH) complex B870 and the reaction-centre (RC) polypeptides (the gene products of the pufB, pufA, pufL and pufM genes) are mapped on a 2.728 kbp EcoRI fragment. Sequencing of this fragment revealed that the deduced amino acid sequences contain 50 (B870 beta), 52 (B850 alpha), 283 (RCL) and 331 (RCM) residues with the corresponding molecular weights of 5592, 5814, 31364, and 37671, respectively. In the corresponding mRNA a 'hairpin' structure (delta G degrees = -26.6 kcal) is predicted to be located immediately downstream of pufA. The RC and LH polypeptides are highly homologous to those of the purple photosynthetic bacteria Rhodobacter capsulatus, Rhodobacter sphaeroides and Rhodopseudomonas viridis. Directly downstream of pufM there is an open reading frame (ORF) of unknown size. Partial sequencing indicates that this ORF is highly homologous to the cytochrome subunit of the photosynthetic reaction centre from R. viridis. In the puf operon no pufQ or pufX genes could be found, but the bchA gene is located upstream of that operon. Plasmid pESS8.9 containing the 2.728 kbp EcoRI fragment reconstituted a photoinactive mutant of Erythrobacter species OCH114. Comparative analysis of the DNA region upstream of the puf operon and of bacteriochlorophyll (Bchl) synthesis indicated that Bchl synthesis and puf gene expression are regulated differently in Erythrobacter and purple bacteria, respectively.

Overlapping mRNA transcripts of photosynthesis gene operons in Rhodobacter capsulatus

The crtEF, bchCA, and puf operons of the facultative phototrophic bacterium Rhodobacter capsulatus encode gene products that are necessary for the formation of various components of the photosynthetic apparatus. The crtEF operon encodes two enzymes involved in the biosynthesis of carotenoids, the bchCA operon codes for two enzymes of the bacteriochlorophyll biosynthetic pathway, and the puf operon encodes four pigment-binding polypeptides as well as two polypeptides with less well understood functions. These three operons are adjacent to one another on the chromosome and are transcribed in the same direction. We present the results of RNA blotting and S1 nuclease protection end-mapping experiments which provide direct evidence that the mRNA transcripts of these three operons overlap. Therefore, it is likely that the crtEF, bchCA, and puf operons can be expressed as a single transcriptional unit, although RNA polymerase may initiate transcription at any of several promoters.

Use of the membrane-impermeable guanidinating reagent 2-S-[14C]thiuroniumethanesulfonate to demonstrate the orientation of light-harvesting proteins in Rhodobacter sphaeroides

The radiolabeled guanidinating reagent 2-S-[14C]thiuroniumethanesulfonate reacts with the epsilon-amino groups of accessible lysyl residues of membrane proteins under relatively mild labeling conditions, yielding labeled homoarginyl residues. Model studies have shown that the resulting homoarginyl residues do act as new cleavage sites for trypsin, but only at a very slow rate of hydrolysis. The reagent has been shown to be impermeable to the intracytoplasmic membranes of Rhodobacter sphaeroides: when cytoplasmic-side-out chromatophores were treated with the reagent, it reacted with all four of the light-harvesting proteins, all of which have one or more lysyl residues on the N-terminal sides of their hydrophobic regions. However, when periplasmic-side-out vesicles, prepared by cytochrome c affinity chromatography, were treated with the guanidinating reagent, three of the light-harvesting proteins (B850 alpha, B850 beta, and B870 beta) were not labeled. The only light-harvesting protein to be labeled (B870 alpha) was the only one of the four to have a lysyl residue on the C-terminal side of its hydrophobic region. Guanidinated B870 alpha polypeptides from both the cytoplasmic-side-out chromatophores and the periplasmic-side-out membrane vesicles were purified and digested with trypsin. The resulting peptide fragments were then separated by high-performance liquid chromatography and analyzed for radioactivity. The results have confirmed the asymmetric orientation of the light-harvesting proteins of R. sphaeroides, with their N-termini on the cytoplasmic side of the intracytoplasmic membrane. In the case of the B870 alpha subunit, the protein has been shown to be transmembrane with its C-terminus on the periplasmic side of the membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Complementation of a reaction center-deficient Rhodobacter sphaeroides pufLMX deletion strain in trans with pufBALM does not restore the photosynthesis-positive phenotype

The puf operon in Rhodobacter sphaeroides is composed of the genes for the photosynthetic reaction center L and M subunits, light-harvesting antenna complex I, and one other open reading frame termed pufX. Complementation of a reaction center-deficient, photosynthetically incompetent pufLMX deletion strain in trans with a fragment containing the entire puf operon, including pufX and an additional 1,100 base pairs of DNA downstream of pufX, restored the reaction center and the photosynthesis-positive phenotype. Complementation of the same strain with pufBALM restores the reaction center to the level seen with the entire puf operon but not the photosynthesis-positive phenotype. Northern (RNA) blot analysis revealed that oxygen regulated transcription was not blocked in the absence of pufX and the downstream region. Spectroscopic and protein analyses indicated that the pigment-binding protein complexes, including the reaction center, were expressed and showed normal absorption characteristics. A 20% reduction in the amount of light-harvesting antenna complex II and a corresponding increase in the amount of light-harvesting antenna complex I were observed in the deletion strain harboring the plasmid with the puf insert lacking the pufX gene and the downstream region compared with those complemented with the entire puf operon and an additional downstream 1,100 base pairs.

Genes downstream from pucB and pucA are essential for formation of the B800-850 complex of Rhodobacter capsulatus

The formation of the light-harvesting complex B800-850 (LH-II) of Rhodobacter capsulatus requires, in addition to the synthesis of the polypeptides alpha and beta (the gene products of pucA and pucB), the synthesis of bacteriochlorophyll and carotenoids and the expression of at least one gene localized downstream from the pucBA operon. This was concluded from the observation that a Tn5 insertion downstream from pucBA inhibited the formation of the LH-II complex and the formation of the pucBA mRNA. The Tn5 insertion point was mapped and found to be over 500 base pairs (bp) downstream from the end of the pucA gene, suggesting the presence of additional puc genes. A region of about 3,000 bp including the pucB and pucA genes and DNA downstream from pucA was sequenced and found to contain three open reading frames (ORFs C, D, and E). The polypeptide deduced from the first ORF (C) contains 403 amino acids with strongly hydrophobic stretches and one large and three small hydrophilic domains carrying many charged residues. The other two ORFs contain 113 (D) and 118 (E) codons. The amino acid sequences of the N terminus and two tryptic peptides of an alkaline-soluble Mr-14,000 subunit of the isolated LH-II complex were identical with the deduced amino acid sequence of ORF E.

Pleiotropic effects of localized Rhodobacter capsulatus puf operon deletions on production of light-absorbing pigment-protein complexes

The polycistronic puf operon of Rhodobacter capsulatus encodes protein components for the photosynthetic reaction center and one of the two antenna complexes involved in the capture of light energy. We report here that deletions within specific puf genes alter the synthesis and/or assembly in the photosynthetic membranes of pigment-protein complexes not affected genetically by the deletion. The pufX gene is required for normal ratios of antenna complexes, and its deletion results in an increase of membrane-bound light-harvesting I (LHI) complex-specific proteins. Expression of pufQ in strains deleted for the genes encoding the LHI and the photosynthetic reaction center (RC) yields a novel A868 peak that has not been associated with any of the pigment-protein complexes described previously. While deletions in the RC-coding region resulted in decreased LHI absorbance, no quantitative alteration in membrane-bound LHI protein was observed, suggesting that an intact RC complex is required for correct assembly of LHI in the membrane.

Roles of bacteriochlorophyll and carotenoid synthesis in formation of intracytoplasmic membrane systems and pigment-protein complexes in an aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh114

Synthesis of bacteriochlorophyll and carotenoids was inhibited in an aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh114, by alpha, alpha'-dipyridyl and diphenylamine. Formation of two pigment-protein complexes, reaction center-B870 (RC-B870) and B806, and development of the intracytoplasmic membranes of the cells were studied by spectral analysis and electron microscopy. Inhibition of bacteriochlorophyll synthesis by alpha, alpha'-dipyridyl, which was accompanied by a decrease in carotenoid synthesis, suppressed formation of intracytoplasmic membranes in the cells. Growth under illumination had a similar effect on formation of pigments and membranes. On the other hand, inhibition of carotenoid synthesis by diphenylamine did not suppress either development of the membrane system or bacteriochlorophyll synthesis. Formation of RC-B870 and B806 complexes, however, was differentially affected by blockage of carotenoid synthesis. In the presence of diphenylamine, the B806 complex was formed in a much smaller amount than the RC-B870 complex. These results suggest that, in Erythrobacter sp. strain OCh114, bacteriochlorophyll plays an essential role in intracytoplasmic membrane development, and carotenoids are important for assembly of pigment-protein complexes.

Effect of oxygen on levels of mRNA coding for reaction-centre and light-harvesting polypeptides of Rhodobacter sphaeroides

The relative levels of mRNA for the reaction-centre L and M subunits, B875 (LH1) alpha and beta polypeptides and B800-850 (LH2) alpha and beta polypeptides, have been measured during pigment induction of Rhodobacter sphaeroides. Over the 6 h of the experiment, bacteriochlorophyll levels increased by at least 100-fold. No transcripts for photosynthetic components were detectable at the start of induction; after 2 h the levels of transcripts from the puf operon (encoding reaction-centre and B875 subunits) had reached the maximum; these transcripts were 2.7 and 0.5 kb respectively. The transcript for the puc operon (B800-850 complex) was estimated to be 0.55 kb and reached a maximum level after 6 h. These results are consistent with the proposal that, during the assembly of the photosynthetic apparatus, the synthesis of B875 reaction-centre aggregates precedes that of the major antenna, B800-850.

Differential expression of photosynthesis genes in R. capsulata results from segmental differences in stability within the polycistronic rxcA transcript

We report that the light-harvesting and reaction center genes in the rxcA locus of R. capsulata are contained within a single operon and that their differential expression results predominantly from marked segmental differences in stability within the polycistronic rxcA transcript. The 3' portion of this transcript is rapidly degraded to give rise to either of two slowly decaying mRNA remnants, both of which encode only the light-harvesting polypeptides. The greater stability of these remnants accounts for nearly all of the difference between the concentrations of the light-harvesting and reaction center proteins. The unstable 3' portion of the transcript is delimited by two alternative stem-and-loop structures, which apparently act as barriers to 3' exoribonucleases and thereby protect the upstream RNA segment. When a DNA fragment containing the rxcA locus was fused to a plasmid promoter and transcribed in E. coli, the long precursor transcript was processed to two short messages of greater stability, as in R. capsulata.

Construction of a gene bank of Rhodopseudomonas capsulata using a broad host range DNA cloning system

A gene bank of the phototrophic bacterium Rhodopseudomonas capsulata was constructed using the binary plasmid system pRK290/pRK2013. Fragments of about 20 kb of chromosomal DNA of R. capsulata strain 37b4 were inserted into the cloning vector pRK290. The hybrid plasmids of the gene bank, maintained in Escherichia coli HB101 were transferred by conjugation to R. capsulata strains defective in the photosynthetic apparatus with frequencies of 5 X 10(-4) to 5 X 10(-2). Phototrophically growing transconjugants occurred with frequencies of 5 X 10(-7) to 5 X 10(-6). Recombination between the hybrid plasmids and the R. capsulata chromosome was shown. The hybrid plasmid pRCF1002, carrying a 25 kb insert of R. capsulata wild type DNA, was isolated from one E. coli clone of the gene bank. It reconstituted some bacteriochlorophyll- and photosynthetic negative mutants to phototrophic growth.

Induction of the photosynthetic membranes of Rhodopseudomonas sphaeroides: biochemical and morphological studies

Cells of Rhodopseudomonas sphaeroides grown in a 25% O2 atmosphere were rapidly subjected to total anaerobiosis in the presence of light to study the progression of events associated with the de novo synthesis of the inducible intracytoplasmic membrane (ICM). This abrupt change in physiological conditions resulted in the immediate cessation of cell growth and whole cell protein, DNA, and phospholipid accumulation. Detectable cell growth and whole cell protein accumulation resumed ca. 12 h later. Bulk phospholipid accumulation paralleled cell growth, but the synthesis of individual phospholipid species during the adaptation period suggested the existence of a specific regulatory site in phospholipid synthesis at the level of the phosphatidylethanolamine methyltransferase system. Freeze-fracture electron microscopy showed that aerobic cells contain small indentations within the cell membrane that appear to be converted into discrete ICM invaginations within 1 h after the imposition of anaerobiosis. Microscopic examination also revealed a series of morphological changes in ICM structure and organization during the lag period before the initiation of photosynthetic growth. Bacteriochlorophyll synthesis and the formation of the two light-harvesting bacteriochlorophyll-protein complexes of R. sphaeroides (B800-850 and B875) occurred coordinately within 2 h after the shift to anaerobic conditions. Using antibodies prepared against various ICM-specific polypeptides, the synthesis of reaction center proteins and the polypeptides associated with the B800-850 complex was monitored. The reaction center H polypeptide was immunochemically detected at low levels in the cell membrane of aerobic cells, which contained no detectable ICM or bacteriochlorophyll. The results are discussed in terms of the oxygen-dependent regulation of gene expression in R. sphaeroides and the possible role of the reaction center H polypeptide and the cell membrane indentations in the site-specific assembly of ICM pigment-protein complexes during the de novo synthesis of the ICM.

Nucleotide and deduced polypeptide sequences of the photosynthetic reaction-center, B870 antenna, and flanking polypeptides from R. capsulata

The complete nucleotide sequence (8867 bp) and the deduced polypeptide sequence are given for 11 proteins from the photosynthetic gene cluster of R. capsulata (46 kb), including the photosynthetic reaction-center L, M, and H subunits and the B870 alpha and B870 beta polypeptides (light-harvesting I). These polypeptides bind bacteriochlorophyll, bacteriopheophytin, carotenoids, and quinones that are involved in the primary light reactions of photosynthesis. Hydropathy plots indicate that the L and M subunits are transmembrane proteins that may cross the membrane five times, while the H subunit has only one hydrophobic section near the amino terminus, which may be transmembrane. The L and M subunits are homologous over their entire length and have a high degree of homology with the QB protein from photosystem II of higher plants. An additional six genes were identified that may have some unknown role in bioenergetics since only mutations that affect the differentiation of the photosynthetic apparatus are known to map to this gene cluster.

Molecular-organization and biosynthesis of pigment-protein complexes of Rhodopseudomonas capsulata

The photosynthetic apparatus of the facultative phototrophic bacterium Rhodopseudomonas capsulata contains three bacteriochlorophyll-carotenoid-protein complexes: the reaction center and the light-harvesting (LH) antenna complexes LHI (B870) and LHII (B800--850). In contrast to green anoxygenic phototrophic bacteria and the oxygenic cyanobacteria, the light-harvesting complexes of Rhodospirillaceae and Chromatiaceae are integral membrane particles. Variations in light fluxes induce membrane differentiation mainly expressed as variations in the size of the photosynthetic unit and in the area of intracytoplasmic membrane per cell. The B800--850 complex is the variable part of the photosynthetic apparatus. Synthesis of bacteriochlorophyll and of the polypeptides of the pigment complexes was found to be strongly coordinated. The synthesis of these polypeptides was followed immediately by the assembly of the complexes in the membrane. Bacteriochlorophyll or a signal substance triggered by bacteriochlorophyll synthesis regulated the synthesis of these polypeptides at the level of translation. The pigment-binding subunits of the B800--850 complex form oligomeric structures which interact with subunit H of the reaction center. A model of the topographical relationships of the pigment complexes is discussed.

The polypeptide components from light-harvesting pigment-protein complex II (B800-850) of Rhodopseudomonas capsulata. Solubilization, purification and sequence studies

A new procedure for isolation, purification and identification of the three polypeptides of the membrane-bound light-harvesting complex II (B800-850) of Rhodopseudomonas capsulata has been developed. The polypeptides were extracted from crude intracytoplasmic membranes with chloroform/methanol/ammonium acetate and separated by chromatography on Sephadex LH60. The peak fractions were transferred to solvents of different polarity and separated by gel filtration or ion-exchange chromatography. The three major polypeptides isolated by this two-step chromatography were found to be homogenous and identical with the three polypeptides of the light-harvesting complex II, as judged by amino acid analysis and N-terminal sequence determination. Contaminating minor polypeptides, of which the functions are unknown, were different from the polypeptides of the B800-850 complex studied by the same criteria.

Fluorescence emission by wild-type- and mutant-strains of Rhodopseudomonas capsulata

Absorption and fluorescence emission spectra of Rhodopseudomonas capsulata, strains 37b4 (wild type), A1a+ (blue-green mutant strain), Y5 (phototroph negative, having only B-800--850 bacteriochlorophyll-carotenoid-protein complex) at 4 K, 77 K and 300 K were measured. The fluorescence emission at 890 nm of the B-870 bacteriochlorophyll band dominates the emission of other spectral forms of the strains 37b4 and A1a+, while in strain Y5 a fluorescence emission band at 865 nm of the B-850 bacteriochlorophyll dominates. Very little fluorescence was observed at 805 nm. A linear relation between relative fluorescence intensity and the exciting light intensity was observed. The integrated fluorescence yield increased as the temperature was lowered from 300 K to 4 K. The results are discussed in the light of the arrangement of pigment molecules in the membrane and the process of energy migration within the photosynthetic apparatus.

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.

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.

Identification of the carotenoid present in the B-800-850 antenna complex from Rhodopseudomonas capsulata as that which responds electrochromically to transmembrane electric fields

Mild proteolysis of Rhodopseudomonas capsulata chromatophores results in a parallel loss of the 800 nm bacteriochlorophyll absorption band a blue shift in the carotenoid absorption bands associated with the B-800-850 light-harvesting complex. Both the light-induced and the salt-induced electrochromic carotenoid band shift disappear in parallel to the loss of the 800 nm bacteriochlorphyll absorption upon pronase treatment of chromatophores. During the time required for the loss of the 800 nm bacteriochlorophyll absorption and the loss of the electrochromic cartenoid band shift photochemistry is not inhibited and the ionic conductance of the membrane remains very low. We conclude that the carotenoid associated with the B-800-850 light-harvesting complex is the one that responds electrochromically to the transmembrane electric field. Analysis of the pigment content of Rps. capsulata chromatophores indicates that all of the carotenoid may be accounted for in the well defined pigment-protein complexes.

Correlation of membrane-potential-sensing carotenoid to pigment-protein complex II in Rhodopseudomonas sphaeroides

The changes in carotenoid absorbance induced by illumination or by a diffusion potential were larger in chromatophores from cells cultured under low light intensity than those in chromatophores from high-light culture in a photosynthetic bacterium, Rhodopseudomonas sphaeroides. The carotenoid molecules which are associated with the pigment-protein complex (with the infrared bacteriochlorophyll peaks at 800 and 850 nm) (complex II) probably respond to the electrical field changes in the chromatophore membrane.

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.

Membranes of Rhodopseudomonas sphaeroides. VI. Isolation of a fraction enriched in newly synthesized bacteriochlorophyll alpha-protein complexes

Radioactivity eventually destined for the chromatophore membrane of Rhodopseudomonas sphaeroides was shown in pulse-chase studies to appear first in a distinct pigmented fraction. The material formed an upper pigmented band which sedimented more slowly than chromatophores when cell-free extracts were subjected directly to rate-zone sedimentation on sucrose density gradients. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the purified fraction contained polypeptide bands of the same mobility as light-harvesting bacteriochlorophyll alpha and reaction center-associated protein components of chromatophores; these were superimposed upon cytoplasmic membrane polypeptides. The pulse-chase relation was confined mainly to the polypeptide components of these pigment-protein complexes. It is suggested that the isolated fraction may be derived from sites at which new membrane invagination is initiated.

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.