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PubMed1978

Spectral properties of chlorophyll a monolayers in the presence of an exogenous electron donor and acceptor.

Chlorophyll a monolayers are studied at a nitrogen-water interface in the presence of a reducing or oxidizing agent: sodium ascorbate and benzyl viologen, respectively. Absorption spectra of the films are measured directly on the aqueous surface. With the aid of a computer, fourth derivative and difference spectra are determined. In the presence of ascorbate, a bathochromic shift of the absorption maximum to 693 nm can be induced as compared to 683 nm for a chlorophyll monolayer without any additives. In the presence of ascorbate, chlorophyll species at 676, 712 and 750 nm (present in a pure chlorophyll monolayer) are decreased or diminished. Illumination causes no change in the position of these absorption maxima; however, there is an increase of the absorbance of the main red absorption band. In the presence of benzyl viologen there is a hypsochromic shift of the red absorption maximum to 679 nm. Chlorophyll species at 670, 694, 712 and 740 nm (present in pure chlorophyll monolayers) are decreased or diminished upon addition of benzyl viologen. Upon illumination, there is a decrease in absorbance at 686 nm. It appears that the redox reagents induce the formation of specific chlorophyll aggregates, in the interfacial system, which might be analogous to the various chlorophyll species observed in green plant photosynthesis.

Ascorbic Acid↗
PubMed1978

The plastid membranes of barley (Hordeum vulgare). Light-induced appearance of mRNA coding for the apoprotein of the light-harvesting chlorophyll a/b protein.

Illumination of dark-grown barley plants induces a massive insertion of the light-harvesting chlorophyll a/b protein into the developing thylakoid membrane. In addition to the onset of chlorophyll synthesis, light induces specifically the appearance of a prominent mRNA species which codes for a polypeptide of Mr 29500. This component was identified as a precursor of the apoprotein of the light-harvesting chlorophyll a/b protein. The precursor has an Mr larger than the authentic protein by approximately 4000. Studies of the chlorophyll-b-less mutant chlorina f2 of barley offer the first clue to the mechanism which controls the light-dependent mRNA formation. The induction of the mRNA coding for the aproprotein of the light-harvesting chlorophyll a/b protein does not seem to be linked directly to the assembly process of the light-harvesting structure and does not require chlorophyll b. It is proposed that light exerts its influence on the mRNA formation by a reaction which is different from the phototransformation of protochlorophyll(ide) to chlorophyll(ide).

Cell Membrane↗
PubMedDate not supplied

[ESR of adsorbed chlorophyll a].

Oxygen and water vapour effect on the dark ESR signal of chlorophyll a adsorbed on silica in vacuum has been studied. It has been determined that when O2 and H2O are absent chlorophyll a adsorption is accompanied by an increase of the paramagnetic states portion (PSP) of the pigment. The PSP is increasing when oxygen is admitted. Water vapour does not increase the PSP of the adsorbed chlorophyll a. It has been supposed that the ESR signal of chlorophyll a in solution belongs to the chlorophyll-oxygen complex and that any strengthening of the pi-pi-interactions results in intensification of the ESR signal. It has been concluded that the ESR signal of adsorbed chlorophyll a belongs to the charge transfer complex of the molecular oxygen and the chlorophyll aggregate with strong pi-pi-interactions.

Adsorption↗
PubMedDate not supplied

Properties of chlorophyll on plasticized polyethylene particles.

There are several reasons for suspecting that there is a specific interaction between chlorophyll and galactolipids in the chloroplast. The model system described is intended to detect association of chlorophyll with polar lipids and other surfactants at a hydrocarbon-water interface. It consists of chlorophyll and other lipids or surfactants absorbed to the surface of polyethylene particles, which have been swelled with undecane to allow the lipophilic parts of these molecules to be anchored firmly in the hydrocarbon substrate. The absorption spectrum of adsorbed chlorophyll is usually modified by the presence of surfactant, and usually in the direction of decreased order of aggregation. Spectra in the presence of glycolipids in particular seem peculiar to the surfactant. The particles are strongly fluorescent, at room temperature as well as at 77K, and emission bands from aggregated chlorophyll species are observed along with fluorescence of monomeric chlorophyll.

Chlorophyll↗
PubMed1978

Functional and structural organization of chlorophyll in the developing photosynthetic membranes of Euglena gracilis Z. II. Formation of system II photosynthetic units during greening under optimal light intensity.

The relationships between light-harvesting chlorophyll and reaction centers in Photosystem II were analyzed during the chloroplast development of dark-grown, non-dividing Euglena gracilis Z. Comparative measurements included light saturation of photosynthesis, oxygen evolution under flashing-light and fluorescence induction. The results obtained can be summarized as follows: (1) Photosystem II photocenters are formed in parallel with chlorophyll synthesis, but after a long lag phase. (2) As a consequence, the chlorophyll reaction center ratio (Emerson's type photosynthetic unit) decreases during greening. (3) This decrease is accompanied by considerable changes in the energy transfer and trapping properties of Photosystem II. Most of the initially synthesized chlorophylls are inactive in the transfer of excitations to active photochemical centers and are shared among newly formed Photosystem II photocenters; as a consequence, the number of chlorophylls functionally connected to each Photosystem II photocenter decreases and cooperatively between these centers appears. Results are discussed in terms of chlorophyll organization in developing photosynthetic membranes with reference to the lake or puddle models of photosynthetic unit organization.

Chlorophyll↗
PubMed1978

Use of immobilized light-harvesting chlorophyll a/b protein to study the stoichiometry of its self-association.

D. J. Davis & E. L. Gross (1976) Biochim. Biophys. Acta 449, 554-564 previously observed that the light-harvesting chlorophyll a/b protein or chlorophyll protein complex II self-associated as determined by ultracentrifugation. We have determined the stoichiometry of complex formation by immobilizing the monomer on ethylenediamine-Sepharose 4B and determing the ability of immobilized protein to bind the free protein. The amount of soluble protein bound to the immobilized protein increased as the concentration of soluble protein increased. The binding was maximal between pH 7 and 8. The maximum binding was three molecules bound per one molecule of protein immobilized. These results indicate that a tetramer is the intrinsic structural unit of the light-harvesting chlorophyll a/b protein in the chloroplast membrane. Upon complex formation, the chlorophyll fluorescence was decreased without any spectral change. The maximum binding was approximately doubled upon addition of 0.5 mM CaCl2 whereas 5 mM NaCl had no effect. Addition of CaCl2 had no effect on the fluorescence of the monomer. The light-harvesting chlorophyll a/b protein can be isolated from a sodium lauryl sulfate extract of chloroplasts by affinity chromatography using the immobilized light-harvesting chlorophyll a/b protein.

Cations↗
PubMedDate not supplied

Enzymic capacities for chlorophyll biosynthesis. Activation and de novo synthesis of enzymes.

A previously published working model for the regulation of chlorophyll formation has been tested studying early steps of chlorophyll and porphyrin biosynthesis in developing cotyledons of Helianthus annuus. The activities of delta-aminolevulinate synthetase (ALAS), delta-aminolevulinate dehydratase (ALAD), and the porphobilinogenase complex (PBGase) at any given time have been found to be strongly associated with endogenous developmental processes. Highest activities in darkness have been observed at times when maximum chlorophyll formation would have occurred had the plants been exposed to light. Only in the case of ALAS was the maximum activity in light much greater than that observed in the dark. Density labeling experiments and other data suggest that enzyme synthesis is mediated both by development and by illumination. Moreover, ALAS activity appears to be subject to inhibition, presumably by products of the porphyrin biosynthesis, as indicated by halflife experiments. Rapid enzyme degradation in the absence of light seems to be less probable. Slight ALAS activity in darkness is present as long as the plastids are not fully developed. In contrast to findings with cell cultures of tobacco, in Helianthus cotyledons ALAS certainly plays the main role in the regulation of chlorophyll biosynthesis. Nevertheless, increasing activities of the succeeding enzymes, located in the plastids, ensure that increased concentrations of delta-aminolevulinate (ALA) are drawn into the chlorophyll biosynthetic pathway. The experiments corroborate the suggestion that chlorophyll biosynthesis is controlled by different but interdependent mechanisms. The dominant regulatory mechanism is dependent on the stage of development.

5-Aminolevulinate Synthetase↗
PubMedDate not supplied

[Absorption spectra of chlorophyll a adsorbed on aerosil].

The adsorption spectra of chlorophyll a adsorbed on aerosil surface have been studied. It has been supposed that the spectral properties of adsorbed chlorophyll a layers are mainly due to the interactions between the pigment molecules. The derivative absorption spectra of adsorbed chlorophyll a have been obtained. It has been determined that descrete absorption maxima of adsorbed chlorophyll a aggregates are characteristic of the native chlorophyll a. It has been supposed that the fundamental spectral forms of chlorophyll a in vivo are reproduced in adsorbed layers of the pigment.

Adsorption↗
PubMedDate not supplied

Resonance Raman spectroscopy of chlorophyll-protein complexes.

Resonance Raman spectra of chlorophyll a (Chl a) and of Chl b were selectively obtained, at low temperature, from chlorophyll-protein complexes prepared from green and blue-green algae and from higher plants. Antenna Chl a in the Chl a-P700-protein complexes (CP I) and in the light-harvesting Chl a/b-protein complexes (CP ii gives resonance Raman spectra extremely close in all their features to those previously obtained from intact cells and chloroplasts. In particular, the same multiplicity of binding sites for the ketone carbonyl groups of Chl a is observed in both CP I and CP II as in intact membranes. These bindings sites are probably the same types as those observed in the intact membranes and are not the magnesium atoms of other chlorophylls. The magnesium atoms of most Chl a molecules in both CP I and CP II bind a single external ligand. Resonance Raman spectra of Chl b in CP II preparations, although very similar to those from intact membranes, show partial rearrangement of one of the two environmental subspecies of Chl b previously found in intact membranes. These results provide evidence that chlorophyll-protein complexes closely represent the state of the bulk of antenna chlorophyll in vivo.

Binding Sites↗
PubMed1977

Possible role of cyclic AMP in the synthesis of chlorophyll in Chlorella fusca.

The intracellular concentration of cAMP in the green alga Chlorella fusca was in the range of 2.10(-9) to 10(-8) moles/g dry weight and was strongly dependent on the growth conditions. The cAMP level was high with high light intensity, low nitrate or glucose concentration. Intracellular cAMP increased only by factor of 2 when high amounts (up to 10(-3) M) of cAMP were added to the medium. Most of the given cAMP was converted to 5'-AMP. Addition of cAMP had little effect on the chlorophyll content of the cells, only at 10(-6) M some enhancement in photoautotrophic cultures was observed. On the other hand high amounts of cAMP in the medium increased the growth rate. DBcAMP* showed a positive effect on chlorophyll synthesis and growth rate at much lower concentrations compared to cAMP. Stimulation effects of exogenous cAMP on the synthesis of chlorophyll were also observed in mixotrophic cultures with a high glucose/nitrate ratio, conditions where chlorophyll synthesis is repressed. Similar to autotrophic conditions DBcAMP was more effective than cAMP. These data indicate that cAMP may act in a system controlling the chlorophyll content of the cells in response to nutrients or light.

Chlorella↗
PubMed1977

Intramembranous particles and chlorophyll complexes in chloroplasts.

The size and population density of large and small particles from freeze-fractured chloroplasts of three wild-type algae and of normal spinach were determined. Computer analyses of low-temperature absorption spectra of chloroplast preparations from these species were performed, and a possible correlation between the occurrence of seven chlorophyll complexes and the aforementioned properties of the intramembranous particles was studies. It was found that only single-sized particles occur in a species containing neither chlorophyll b nor chlorophyll a-685 complexes. The three remaining species carry particles of two sizes, termed large and small particles. However, from quantitative considerations it is concluded that the chlorophyll content of none of the various pigment complexes is related to the size and the population density of the studied particles. If such a relationship exists, it seems likely to be due to the carrier moiety of the chorophyll b-chlorophyll a-685 complex.

Chlorophyll↗
PubMed1978

Polypeptide profiles of chlorophyll . protein complexes and thylakoid membranes of spinach chloroplasts.

In addition to the major chlorophyll . protein complexes I and II, two minor chlorophyll proteins have been observed in sodium dodecyl sulfate (SDS))-polyacrylamide gels of spinach chloroplast membranes. These minor pigmented zones appeared to be derived from the light-harvesting chlorophyll a/b . protein and from the reaction centre complex of Photosystem II. Data are presented on the polypeptide profiles of purified digitonin-subschloroplast particles, with special regard to the effect of solubilization temperature and extraction of lipids. The results are compared with the SDS-polypeptide pattern of spinach thylakoids obtained under exactly the same conditions with respect to electrophoresis technique, solubilization method and presence of lipid. In addition, the effects of temperature and lipid extraction on the distinct chlorophyll . protein complexes appearing in SDS gel electrophoretograms of chloroplast membranes were studied by slicing the chlorophyll-containing regions and subjecting them to a second run with or without heating or extraction with acetone. By supplementing these data with an examination of the polypeptide composition of cytochrome f and coupling factor, it has been possible to identify most of the major chloroplast membrane polypeptides.

Cell Membrane↗
PubMed1979

The electrophoretic isolation and partial characterization of three chlorophyll-protein complexes from blue-green algae.

Three chlorophyll-protein complexes have been resolved from blue-green algae using an improved procedure for membrane solubilization and electrophoretic fractionation. One complex has a red absorbance maximum of 676 nm and a molecular weight equivalency of 255 000 +/- 15 000. A second complex has an absorbance maximum of 676 nm, a molecular weight equivalency of 118 000 +/- 8000, and resembles the previously described P-700-chlorophyll a-protein (CPI) of higher plants and algae. The third chlorophyll-protein has a red absorbance maximum of 671 nm and a molecular weight equivalency of 58 000 +/- 5000. Blue-green algal membrane fractions enriched in Photosystem I and heterocyst cells do not contain this third chlorophyll-protein, whereas Photosystem II-enriched membrane fractions and vegetative cells do. A component of the same spectral characteristics and molecular weight equivalency was also observed in chlorophyll b-deficient mutants of barley and maize. It is hypothesized that this third complex is involved in some manner with Photosystem II.

Chlorophyll↗
PubMed1977

The oxidation-reduction potential of the reaction-centre chlorophyll (P700) in Photosystem I. Evidence for multiple components in electron-paramagnetic-resonance signal 1 at low temperature.

The oxidation-reduction potential of the reaction-centre chlorophyll of Photosystem I (P700) in spinach chloroplasts was determined by using the ability of the reaction centre to photoreduce the bound ferredoxin and to photo-oxidize P700 on illumination at 20K as an indicator of the oxidation state of P700. This procedure shows that P700 is oxidized with Em (pH8.0)(mid-point redox potential at pH8.0)congruent to +375mV. Further oxidation of the chloroplast preparations by high concentrations of K3Fe(CN)6(10mM) in the presence of mediating dyes leads to the appearance of a large radical signal with an apparent Em congruent to +470mVA second, light-inducible, radical also appears over the same potential range. We propose that these signals are due to bulk chlorophyll oxidation and not, as was previously thought [Knaff & Malkin (1973) Arch. Biochem. Biophys. 159, 555-562], to reaction-centre oxidation. A number of optical techniques were used to determine Em of P700. Dual-wavelength spectroscopy (697-720nm) indicates Em congruent to +460-+480mV. The spectrum of the sample during the titration showed a large contribution to the signal by bulk chlorophyll oxidation, in agreement with the electron-paramagnetic-resonance results and those of Ke, Sugahara & Shaw [(1975) Biochim. Biophys. Acta 408, 12-25]. The light-induced absorbance change at 435 nm, usually attributed to P700, showed a potential dependence similar to that of bulk chlorophyll oxidation. Determination of Em of P700 on the basis of the appearance of the P700 signal in oxidized-versus-reduced difference spectra showed Em (pH8.0) congruent to +360mV. Measurements of the effect of potential on the irreversible photo-oxidation of P700 at 77K showed that P700 became oxidized in this potential range. We conclude that the reaction-centre chlorophyll of Photosystem I has Em (pH8.0) congruent to +375mV.

Chlorophyll↗
PubMed2025

Effects of light on chloroplast translation in Marchantia polymorpha are similar to those in angiosperms and are not influenced by light-independent chlorophyll synthesis.

Translation of the chloroplast psbA mRNA in angiosperms is activated by photodamage of its gene product, the D1 subunit of photosystem II (PSII), providing nascent D1 for PSII repair. The involvement of chlorophyll in the regulatory mechanism has been suggested due to the regulatory roles of proteins proposed to mediate chlorophyll/D1 transactions and the fact that chlorophyll is synthesized only in the light in angiosperms. We used ribosome profiling and RNA-seq to address whether the effects of light on chloroplast translation are conserved in the liverwort Marchantia (Marchantia polymorpha), which synthesizes chlorophyll in both the dark and the light. As in angiosperms, ribosome occupancy on psbA mRNA decreased rapidly upon shifting plants to the dark and was rapidly restored upon a transfer back to the light, whereas ribosome occupancy on other chloroplast mRNAs changed very little. The results were similar in a Marchantia mutant unable to synthesize chlorophyll in the dark. Those results, in conjunction with pulse-labeling data, suggest that light elicits a plastome-wide activation of translation elongation and a specific increase in psbA translation initiation in Marchantia, as in angiosperms. These findings show that light regulates chloroplast translation similarly in vascular and non-vascular plants, and that constitutive chlorophyll synthesis does not affect light-regulated psbA translation initiation. Additionally, the translational outputs of chloroplast genes are similar in Marchantia and angiosperms but result from differing contributions of mRNA abundance and translational efficiencies. This adds to the evidence that chloroplast mRNA abundance and translational efficiencies co-evolve under selection to maintain protein outputs.

Chloroplasts↗
PubMedDate not supplied

[Spectral forms of the chlorophyll of mutants of Chlamydomonas with inactive photosystems].

Investigations of non-photosinthesizing mutants of Chlamydomonas reinhardii with damaged activity of both or one of the photosystems have shown that the chlorophyll a form with the absorption maximum at 685 nm and low temperature fluorescence band at 696 nm is a part of the pigment-protein complex of PS-2. Chlorophyll a forms with absorption maxima at 689, 698 and 703 nm belong to the pigment-protein complex of PS-1. They seem to be responsible for the long-wave band of chlorophyll fluorescence with the maximum at 707--718 nm. Chlorophyll a forms with absorption at 661, 667 and 678 nm and a short-wave fluorescence band at 685--690 nm rank among the pigments of the light-converging complex, as well as chlorophyll b with the absorption maximum at 644 and 649 nm.

Chemical Phenomena↗
PubMedDate not supplied

[Studies of sorption and interaction of chlorophyll and chlorophyllase on methylaerosil].

The article deals with the possibility of chlorophyll and chlorophyllase immobilization on methylaerosil and also with the effect of this carrier on the enzyme-substrate interaction. Chlorophyll and chlorophyllase are shown to be able to hydrophorbic interaction. It is established that the ultimate saturation of methylaerosil with chlorophyll is 16.1 mg per 100 mg of the carrier. The chlorophyllase reaction is the most active under conditions when the enzyme and substrate are in soluble states. The hydropholic binding of chlorophyll with methylaerosil decreases the intensity of its hydrolysis for the period of reaction and the preliminary immobilization of chlorophyllase on methylaerosil inhibits the reaction to a still greater extent. This evidences for the significance of the reaction system organization for interaction of chlorophyllase with chlorophyll.

Carboxylic Ester Hydrolases↗
PubMedDate not supplied

Fluorescence of light-harvesting chlorophyll a/b-protein complexes: implications for the photosynthetic unit.

To the extent that extracted light-harvesting chlorophyll proteins (LHCPs) retain the chlorophyll configuration which they had in vivo, information on the optical properties of LHCPs is useful for an assessment of the transfer process of the primary excitation energy in photosynthesis. Within this context we report and discuss the implication of three kinds of data on spinach chloroplast LHCP. First, an analysis of the spectroscopic dependence of absorption, polarization and circular dichroism (reported recently by R.L.V.) suggests a model affording the possibility of easy chlorophyll a intercomplex transfer with chlorophyll b groups acting as local antitraps. Second, the ratio of LHCP emission and absorption probabilities obeys the Stepanov relation over a relatively wide range, an observation which suggests rapid Chl b-Chl a excitation equilibration. Finally, an LHCP absolute fluorescence yield as great as 10% has been measured, which provides a possible upper limit for the yield of the antenna fluorescence.

Chlorophyll↗