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PubMedDate not supplied

Structure and function of photoreaction-centre chlorophyll.

Evidence from electron paramagnetic resonance (e.p.r.) studies suggests that the unpaired spin in oxidized P700+. or P865+. is shared by two special chlorophyll a (Chl a) or bacteriochlorophyll a (Bchl a) molecules respectively. Three classes of models have been proposed for special pair reaction centre chlorophyll: asymmetric, in which one Chl a (or Bchl a) acts as electron donor to a second acting as acceptor; models with translational symmetry only; and models with C2 symmetry. Models with C2 symmetry have been synthesized in vitro with two chlorophyll macrocycles tied together by a covalent link. The singlet and triplet states of the in vitro models have been characterized by e.p.r., nuclear magnetic resonance, and optical studies involving absorption, emission, and lasting behaviour. The fact that lasting occurs only from the folded configuration of the linked dimers suggests the availability of a highly effective nonradiative decay path from the S1 state of the excited open dimer. A radical-pair mechanism that accounts for the unusual spin polarization of the special pair triplet is proposed for the primary photochemistry in the reaction centre.

Bacteria↗
PubMed1989

Chlorophyll precursors in the plasma membrane of a cyanobacterium, Anacystis nidulans. Characterization of protochlorophyllide and chlorophyllide by spectrophotometry, spectrofluorimetry, solvent partition, and high performance liquid chromatography.

Plasma membranes were isolated and separated from thylakoid membranes by discontinuous sucrose density gradient centrifugation of crude membranes prepared by French pressure cell extrusion of lysozyme-treated Anacystis nidulans. Two distinct populations of chlorophyll-free plasma membrane vesicles were obtained exhibiting buoyant densities of 1.087 and 1.100 g/cm3 as opposed to a uniform density of 1.192 g/cm3 for thylakoid membranes. Plasma and thylakoid membranes were characteristically different also with respect to fatty acid and protein composition, cytochrome oxidase activity, and pigment content as analyzed by spectrophotometry, spectrofluorimetry, and high performance liquid chromatography. Apart from carotenoids, chlorophyll a was the only major photosynthetic pigment detected in thylakoid membranes while plasma membranes contained virtually no chlorophyll a but (besides large amounts of carotenoids) protochlorophyllide a and chlorophyllide a as revealed by solvent partition (between n-hexane and acetone or methanol), room and low temperature fluorescence emission and excitation spectra, and analytical separation and identification by high performance liquid chromatography and comparison with authentic standards. The protochlorophyllide in the plasma membrane could be transformed into chlorophyllide in the dark in vitro by incubating the membrane preparation with NADPH; NADP+ effected the reverse transition.

Cell Membrane↗
PubMed1986

Identification and analysis of the maize P700 chlorophyll a apoproteins PSI-A1 and PSI-A2 by high pressure liquid chromatography analysis and partial sequence determination.

We recently described a pair of partially homologous maize chloroplast genes, one of which was shown to code for an apoprotein of the P700 chlorophyll a complex of photosystem I (Fish, L.E., Kück, U., and Bogorad, L. (1985) J. Biol. Chem. 260, 1413-1421). Two chlorophyll-free apoprotein bands from maize chlorophyll-protein complex I (CPI) can be resolved on lithium dodecyl sulfate (LDS)-urea polyacrylamide gels. Proteins in both bands react with antibodies prepared against CPI, but antibodies prepared against two synthetic peptides corresponding to predicted sequences of PSI-A1 react only with the upper band. The presence of products of the two genes, ps1A1 and ps1A2, in CPI was verified by analysis of cyanogen bromide (CNBr) fragments of the lower apoprotein band obtained from LDS-urea polyacrylamide gels by reverse-phase high pressure liquid chromatography. Amino-terminal sequencing of five CNBr fragments indicates that the lower band contains a product of the ps1A2 gene. The possibility of extensive processing was investigated because the apparent molecular masses of the maize CPI proteins are about 58-70 kDa on LDS-polyacrylamide gels rather than the predicted sizes of about 83 kDa. Antibodies against a synthetic peptide corresponding to a predicted sequence in PSI-A1 were used to determine that the amino-terminal end of PSI-A1 is intact beyond about position 52. The amino-terminal CNBr fragment of PSI-A2 was identified by sequencing, indicating that the amino-terminal end of PSI-A2 is not processed. The carboxyl-terminal CNBr fragment of PSI-A2 was also identified by sequencing. These results indicate that the PSI-A1 and PSI-A2 polypeptides are not extensively processed, although some processing at the carboxyl-terminal end has not been ruled out.

Amino Acid Sequence↗
PubMed1987

Circadian oscillations in chlorophyll fluorescence in a triazine-resistant chronomutant of Brassica napus.

The objectives of this study were to determine if there was variation in atrazine tolerance, measured by intensity of leaf-disc chlorophyll fluorescence, in triazine-resistant and -susceptible Brassica napus in terms of age of leaf on the plant, time of day, and time of assay after leaf disc removal and immersion in atrazine. In a growth room and field experiment, triazine-susceptible B. napus cv. "Tower" and triazine-resistant B. napus cv. "OAC Triton" were used. Chlorophyll fluorescence intensity measurements were made 15-30 min after disc removal. In both environments, two periods of reduced photosynthetic efficiency occurred in the circadian phase. The times that these periods occurred during the diurnal phase differed between biotypes. A phase shift in leaf chlorophyll fluorescence (LCF) maxima between resistant and susceptible biotypes resulted in two periods, early and late in the light phase, of increased LCF in resistant tissue. This differential pattern in LCF is support for the hypothesis that triazine-resistance chloroplast alterations imply an alteration in the temporal organization of chloroplast physiological function. Atrazine reduced the photosynthetic efficiency of resistant tissue in some instances. This could indicate that triazine resistance is not complete and that some metabolic role may be involved. The results reported here indicate that the most accurate estimation of the physiological state will be obtained from LCF measurements taken soon after leaf disc removal from the plant.

Atrazine↗
PubMed1985

Chloroplast biogenesis. Molecular structure of chlorophyll b (E489 F666).

Nuclear magnetic resonance analysis established the presence of two vinyl groups/macrocycle of chlorophyll b (E489 F666). The latter is the only chlorophyll b that accumulates in a corn mutant (ON 8147). On the other hand the presence of only one vinyl group/macrocycle of authentic monovinyl chlorophyll b (E475 F660) was confirmed.

Chlorophyll↗
PubMedDate not supplied

[Chlorophyll-photosensitized reduction of methyl red in detergent solutions].

Chlorophyll-photosensitized reduction of methylene red with ascorbic acid was studied in micellar solutions of triton X-100. The maximum value of photosensitization was observed in the region 0.1% of triton, approximating the critical concentration of micelleformation. The rate of photoreduction of methylene red was strongly influenced by the medium pH, the optimal pH value being 4.8. The specific activity of chlorophyll in the course of photosensitization was shown to depend on its concentration. Specific activity of the monomeric form of chlorophylls a and b (5.3 and 3.2 s-1 respectively) was estimated.

Ascorbic Acid↗
PubMed1983

Nucleotide sequences of two pea cDNA clones encoding the small subunit of ribulose 1,5-bisphosphate carboxylase and the major chlorophyll a/b-binding thylakoid polypeptide.

Two major chloroplast proteins are encoded by nuclear genes and synthesized on free cytoplasmic ribosomes: the small subunit of ribulose 1,5-bisphosphate carboxylase and the apoprotein components of the chlorophyll a/b light harvesting complex. We have recently reported the isolation of two cDNA clones from pea which encode both the small subunit of ribulose 1,5-bisphosphate carboxylase (pSS15) and the polypeptide 15 (pAB96), the major chlorophyll a/b binding protein (Broglie, R., Bellemare, G., Bartlett, S., Chua, N.-H., and Cashmore, A. R. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 7304-7308). To further characterize these clones, we determined their nucleotide sequence. Clone pSS15 contains a 691-base pair cDNA insert which encodes the entire 123 amino acids of the mature small subunit protein. In addition, this clone also encodes 33 amino acids of the NH2-terminal transit peptide extension and 148 nucleotides of the 3' noncoding region preceding the poly(A)tail. A second cDNA clone (pAB96) contains an 833-nucleotide insert which encodes most of polypeptide 15. The DNA sequence of this cloned cDNA was used to deduce the previously undetermined amino acid sequence of this integral thylakoid membrane protein. The nucleotide sequence of the cDNA clone, pSS15, should provide information concerning the role of the transit sequence in the transport of cytoplasmically synthesized chloroplast proteins. Similarly, the deduced amino acid sequence of polypeptide 15 will provide information for predicting its orientation in thylakoid membranes as well as its role in binding chlorophyll.

Amino Acid Sequence↗
PubMedDate not supplied

[Quenching of chlorophyll and pheophytin fluorescence with fucoxanthin].

Quenching of chlorophyll a and pheophytin a fluorescence with fucoxanthin in acetone and n-hexanole at room temperature was investigated. The relationship between fluorescence yield and concentration of the quencher is subject to Stern--Folmer relation. The velocity constants were calculated and the efficiency of fluorescence quenching was determined. The energetic estimation has shown that the fluorescence quenching mechanism when the excited chlorophyll a molecule collides with fucoxanthin molecule may involve electron transfer from chlorophyll to fucoxanthin. In case of pheophytin a transfer of the electron from fucoxanthin to pheophytin is likely to take place.

Carotenoids↗
PubMedDate not supplied

[Quenching of singlet oxygen with chlorophylls and porphyrins].

The rate constants (kox) of irreversible oxidation of chlorophylls and porphyrins by 1 delta g state of oxygen (1O2) have been determined. It has been shown that kox values are 1-5 orders of magnitude lower than the values of rate constants of quenching 1O2 (kq) with the same pigments. The correlation between kox and kq has been found. Its analysis allowed to conclude that oxidation proceeds via intermediate formation of a charge transfer complex between the pigments and 1O2. A kinetic scheme of the processes leading to physical and chemical quenching 1O2 with chlorophylls and porphyrins is proposed, its mathematical analysis is carried out. The results of this analysis can be used for a search of substances capable of effective quenching 1O2 without destruction of the quenchers. It is concluded that chlorophylls protect photosynthetic membranes from the destruction by 1O2, and some synthetic metal-porphyrins can be used as good protectors of different systems against photooxidation.

Chlorophyll↗
PubMed1980

[Photophosphorylation involving chlorophyll adsorbate, separation of light and dark stages].

Upon illumination of the system containing chlorophyll a+b adsorbed on a SiO2 sorbent, ADP and Pi in an aqueous solution, pH 7.6, the formation of ATP has been demonstrated, using 32P-phosphate. This process is inhibited in the absence of oxygen or in the presence of ascorbate. Under similar conditions without ADP pyrophosphate is formed; substitution of ADP for arginine results in a formation of arginine phosphate. Phosphorylation with a reduced yield has also been found upon illumination of chlorophyll adsorbate without other additives and an addition of ADP+Pi solution in the dark to the preilluminated adsorbate fast enough to prevent the decay of the light-induced product. A model according to which the chlorophyll-sensitized oxidation of orthophosphate ion the primary event in the reaction sequence, and the decomposition of orthophosphate radical anion into methaphosphate and hydroxyl species is the secondary step, has been proposed. A possible significance of the results obtained is discussed in terms of the concepts on the prebiotic evolution of energy metabolism.

Adenosine Diphosphate↗
PubMedDate not supplied

[Study of the effect of specific translation inhibitors on formation of native forms of chlorophyll in pigment-protein-lipid complexes of pea chloroplasts].

The effect of specific inhibitors of translation in chloroplasts (chloramphenicol) and in cytoplasm (cycloheximide) on the formation of pigment-protein-lipid complexes of photosynthetic membranes, on the chlorophyll state in chloroplasts and isolated membrane complexes had been studied. It is proved that the inhibition of translation blocks chlorophyll incorporation only into the complexes of reaction centres of photosystems without any change of the light-harvesting complex. The action of inhibitors leads to the disappearance of long-wave native forms of pigment in the complexes of reaction centres, which are characteristic for them. But the action of inhibitors does not effect the formation of non-specific short-wave forms which are present in all types of membrane complexes. Chloramphenicol proved to be more active in such processes than cycloheximide. On the basis of the data on localization of biosynthesis of polypeptide components of plastid membranes we suppose that during biogenesis of the photosynthetic apparatus the conditions for self-assembly of non-specific native forms of chlorophyll in light-harvesting complexes are made as the result of polymerazation of the main membrane polypeptides which are synthesized in the cytoplasms. Minor polypeptides of plastid (photosystems 1 and 2) and cytoplasmic (photosystem 1) orgin are necessary for self-assembly of the dense units of pigment in reaction centre complexes.

Chloramphenicol↗
PubMed1979

The light-harvesting chlorophyll a/b-protein complex from barley thylakoid membranes. Polypeptide composition and characterization of an oligomer.

Electrophoretic analysis by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis showed that the light-harvesting chlorophyll a/b-protein complex of barley thylakoids contains only one polypeptide of apparent molecular weight 26 000. The barley mutant, deficient in chlorophyll b and this light-harvesting complex, lacks this polypeptide. The addition of a nonionic detergent, Triton X-100, to the sodium dodecyl solubilization buffer prior to SDS polyacrylamide tube gel electrophoresis, allowed separation of a relatively stable complex, characterized as an oligomeric form of the light-harvesting complex. The oligomer also contained a polypeptide with an apparent molecular weight of 26 000. The absorption and fluorescence spectral properties of the oligomer are similar to those of the monomer. It is suggested that the oligomer of the light-harvesting chlorophyll a/b-protein is closer to the in vivo form rather than the monomer.

Cell Membrane↗
PubMed1976

Reconstitution of biological molecular generators of electric current. Bacteriochlorophyll and plant chlorophyll complexes.

1. Electric generation by bacteriochlorophyll reaction center complexes from Rhodospirillum rubrum and by photosystem I complexes from pea chloroplasts has been studied. 2. The methods for the proteoliposome reconstitution from azolectin and bacteriochlorophyll- or plant chlorophyll-containing protein complexes have been elaborated. Light-dependent electric responses of the proteoliposomes were detected using (a) phenyldicarbaundecarborane anion (PCB-) probe and (b) direct measurement by a voltmeter in the proteoliposome-planar phospholipid membrane system. 3. Both PCB- and direct measurements demonstrated that bacteriochlorophyll proteoliposomes are competent in light-dependent electric generation (plus outside proteoliposomes). The photoelectric effect was shown to increase on addition of tetramethyl-p-phenylenediamine (TMPD), CoQ6, and vitamin K3, and to decrease on addition of ferricyanide, o-phenanthroline and a protonophorous uncoupler. Estimation of the photoelectromotive force of the bacteriochlorophyll proteoliposome-planar membrane system gave a value of about 0.2 V. The action spectrum of the photoelectric effect was similar to the absorption spectrum of the bacteriochlorophyll complex. 4. Reconstitution of proteoliposomes containing bacteriochlorophyll centers and bacteriorhodopsin resulted in the system generating an electric field whose direction can be changed by varying the spectral composition of the light: the red light, exciting bacteriochlorophyll, induces negative, and the green light, exciting bacteriorhodopsin, induces positive charging of the proteoliposome interior. 5. Association of isolated R. rubrum chromatophores with planar phospholipid membrane was found to give a system demonstrating light-induced electric generation as high as 215 mV in the presence of napthoquinone, TMPD (or phenazine methosulfate, PMS), and ascorbate. Under the same conditions, addition of inorganic pyrophosphate or ATP results in formation of an electric field of the same direction as that induced by light. 6. Proteoliposomes with plant chlorophyll complexes of photosystem I demonstrated light-induced PCB- responses indicating formation of the electric field with plus inside vesicles. The effect required PMS addition. A protonophorous uncoupler and o-phenanthroline were inhibitory. Electric responses in the chlorophyll proteoliposome-planar membrane system were very small (not higher than 10 mV).

Bacterial Chromatophores↗
PubMed1977

Catalase and peroxidase activities, chlorophyll and proteins during storage of pea plants of chilling temperatures.

The effect of chilling temperatures on the catalase and peroxidase activities, soluble proteins and chlorophyll contents of excised organs of Pisum sativum plants has been studied. In leaf and stem tissues, storage at 0 degrees C did not bring about any statistically significant variation in the levels of heme enzymes, proteins and chlorophyll during four days. On the contrary, in root tissues catalase activity experimented a statistically significant depression after the onset of cold storage and during the whole treatment, whereas the other parameters remained nearly constant. Results obtained showed the suitability of storing plant material at 0 degrees C for the stabilization of catalase, peroxidase and chlorophyll in leaves and stems, as well as of peroxidase activity in roots.

Catalase↗
PubMed1983

Localization of the genes for the two chlorophyll a-conjugated polypeptides (mol. wt. 51 and 44 kd) of the photosystem II reaction center on the spinach plastid chromosome.

A core particle of the water-oxidizing photosystem II reaction center has been prepared from stacked spinach thylakoid membranes by a procedure involving extraction with the non-ionic detergent dodecyl-beta-D-maltoside and centrifugation in sucrose gradients. The protein-pigment complex consists of at least four polypeptide species: two components with mol. wts. of 51 and 44 kd which are conjugated with chlorophyll a and beta-carotene, the herbicide-binding protein of mol. wt. 32 kd and cytochrome b 559 (11 kd). The genes for the 51-and 44-kd polypeptides have been located on the circular 150-kbp spinach plastid chromosome. They were identified by hybrid-selection mapping, in vitro transcription-translation of recombinant DNAs and specific antisera which were used to characterize the translation products. The plastid chromosome carries one uninterrupted copy for each of these genes in its large single-copy region. The gene for the 51-kd protein (which probably bears the P(680) reaction center chlorophyll a) is located in close proximity to the gene for cytochrome b6, and some 70 kbp away from the gene for the ;32-kd' herbicide-binding protein of the reducing side of photosystem II. The gene for the 44-kd protein is situated halfway between these two genes adjacent to the gene for the P(700) chlorophyll a apoprotein of the photosystem I reaction center. Both photosystem II genes are transcribed into discrete RNA species in the same direction but from the opposite strand as the gene for the ;32-kd' protein.

Journal Article↗
PubMed1995

Nucleotide sequence of two cDNAs encoding fucoxanthin chlorophyll a/c proteins in the diatom Odontella sinensis.

Two cDNA clones encoding fucoxanthin chlorophyll a/c-binding proteins (FCP) in the diatom Odontella sinensis have been cloned and sequenced. The derived amino acid sequences of both clones are identical, comparison of the corresponding nucleic acids reveals differences only in the third codon position, suggesting a recent gene duplication. The derived proteins are similar to the chlorophyll a/b-binding proteins of higher plants. The presequences for plastid import resemble signal sequences for cotranslational import rather than transit peptides of higher plants. They are very similar to the presequences of FCP proteins in the diatom Phaeodactylum, but different from the presequences of the gamma-subunit of CF0CF1 of Odontella and the peridinin chlorophyll a binding proteins (PCP) of the dinoflagellate Symbiodinium.

Amino Acid Sequence↗
PubMed1994

Structure and light-regulated expression of the gsa gene encoding the chlorophyll biosynthetic enzyme, glutamate 1-semialdehyde aminotransferase, in Chlamydomonas reinhardtii.

The gsa gene, which encodes glutamate 1-semialdehyde (GSA) aminotransferase (GSAT), an enzyme in the chlorophyll and heme biosynthetic pathway, has been cloned from Chlamydomonas reinhardtii by complementation of an Escherichia coli hemL mutant. The deduced C. reinhardtii GSAT amino acid sequence has a high degree of similarity to GSAT sequences from barley, tobacco, soybean and various prokaryotic sources. In vitro enzyme activity assays from E. coli transformed with the C. reinhardtii GSAT cDNA showed that higher levels of GSAT activity are associated with the expression of the cDNA insert. Analysis of changes in mRNA levels in light:dark synchronized C. reinhardtii cultures was done by northern blotting. The level of GSAT mRNA nearly doubled during the first 0.5 h in the light and increased over 26-fold after 2 h in the light. This increase is comparable to previously reported increases in GSAT activity in dark-grown cultures transferred to the light, and is the first report of induction by light of a gene encoding an ALA biosynthetic enzyme in plant or algal cells. The accumulation of GSAT mRNA follows the pattern of chlorophyll accumulation and the pattern of chlorophyll a/b-binding protein (cabII-1) mRNA accumulation in these cells, suggesting that the two genes may be regulated by light through a common mechanism. Additional evidence that the GSAT mRNA may be transcriptionally regulated by light is found in the genomic sequence of the gsa gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

The gene family encoding the fucoxanthin chlorophyll proteins from the brown alga Macrocystis pyrifera.

Six members of a multigene family encoding polypeptide constituents of the fucoxanthin, chlorophyll a/c protein complex from female gametophytes of the brown alga Macrocystis pyrifera have been cloned and characterized. The deduced amino acid sequences are very similar to those of fucoxanthin chlorophyll binding proteins (Fcp) from the diatom Phaeodactylum tricornutum and exhibit limited homology to chlorophyll a/b binding (Cab) polypeptides from higher plants. The primary translation products from the M. pyrifera fcp genes are synthesized as higher molecular weight precursors that are processed prior to their assembly into the Fcp complex. The presumed N-terminal 40-amino acid presequence of the Fcp precursor polypeptide has features resembling that of a signal sequence. This presequence may be required for the protein to transverse the endoplasmic reticulum that surrounds the plastid in brown algae. A subsequent targeting step would be required for the protein to cross the double membrane of the plastid envelope. M. pyrifera fcp transcripts are of two sizes, 1.2 and 1.6 kb. The size difference is accounted for by the length of the 3' untranslated region, which can be up to 1000 bases. Transcript abundance's of members of the fcp gene family are dependent on light quantity, light quality, or both. Transcript levels of one gene increased approximately five- to tenfold in thalli grown in low intensity relative to high intensity white or blue light. Transcripts from this gene also significantly increase in red light relative to blue light at equivalent light intensities.

Amino Acid Sequence↗