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PubMed1980

The protochlorophyllide holochrome of barley (Hordeum vulgare L.). Isolation and characterization of the NADPH:protochlorophyllide oxidoreductase.

The NADPH:protochlorophyllide oxidoreductase of barley has been solubilized from etioplast membranes and purified to apparent homogeneity. The highest specific activity measured for the purified enzyme was 1.6 nmol chlorophyllide formed (mg protein-1) per flash. Electrophoretic analysis of the purified enzyme on sodium dodecylsulfate/polyacrylamide gels revealed only one polypeptide of Mr 36000. Durig glycerol gradient centrifugation the enzyme migrates as a low-molecular-weight component. It is proposed that each enzyme molecule contains only one polypeptide chain. Assuming a molecular weight of 36000 for the enzyme, it was calculated that two or three protochlorophyllide molecules are bound to each enzyme molecule.

Chlorophyll↗
PubMed1986

The implication of a plastid-derived factor in the transcriptional control of nuclear genes encoding the light-harvesting chlorophyll a/b protein.

In carotenoid-deficient albina mutants of barley and in barley plants treated with the herbicide Norflurazon the light-dependent accumulation of the mRNA for the light-harvesting chlorophyll a/b protein (LHCP) is blocked. Thus, the elimination of a functional chloroplast, either as a result of mutation or as a result of herbicide treatment, can lead to the specific suppression of the expression of a nuclear gene encoding a plastid-localized protein. These results confirm and extend earlier observations on maize [Mayfield and Taylor (1984) Eur. J. Biochem. 144, 79-84]. The inhibition of mRNA accumulation appears to be specific for the LHCP; the mRNAs encoding the small subunit of ribulose-1,5-bisphosphate carboxylase and the NADPH: protochlorophyllide oxidoreductase are relatively unaffected. The failure of the albina mutants and of Norflurazon-treated plants to accumulate the LHCP mRNA is not exclusively caused by an instability of the transcript but rather by the inability of the plants to enhance the rate of transcription of the LHCP genes during illumination. Several chlorophyll-deficient xantha mutants of barley, which are blocked after protoporphyrin IX or Mg-protoporphyrin, and the chlorophyll-b-less mutant chlorina f2 accumulate the LHCP mRNA to almost normal levels during illumination. Thus, if any of the reactions leading to chlorophyll formation is involved in the control of LHCP mRNA accumulation it should be one between the formation of protochlorophyllide and the esterification of chlorophyllide a. While the nature of the regulatory factor(s) has not been identified our results suggest that, in addition to phytochrome (Pfr), plastid-dependent factors are required for a continuous light-dependent transcription of nuclear genes encoding the LHCP.

Carotenoids↗
PubMed1995

Photoreduction of zinc protopheophorbide b with NADPH-protochlorophyllide oxidoreductase from etiolated wheat (Triticum aestivum L.).

A preparation of prolamellar bodies from wheat etioplasts was used as a source for NADPH-protochlorophyllide oxidoreductase (pchlide reductase). The enzyme was solubilized with Triton X-100 after reduction of the endogenous photoconvertible protochlorophyllide a to chlorophyllide a by saturating illumination. Protochlorophylls a and b, protochlorophyllide a and zinc protopheophorbide b were added to the soluble enzyme preparation to determine if they were reduced in the dark or in the light. None of the compounds were reduced (with NADPH) in the dark; however, light-dependent reduction was demonstrated with protochlorophyllide a and zinc protopheophorbide b. The yield was approximately 50% for both substrates. Photoreduction did not occur with the esterified protochlorophylls a and b. Photoreduction of zinc protopheophorbide b, the zinc analogue of protochlorophyllide b, is the first demonstration of the reduction of a chlorophyll-b-related compound by pchlide reductase.

Chlorophyll↗
PubMed2005

Mg-protoporphyrin IX and heme control HEMA, the gene encoding the first specific step of tetrapyrrole biosynthesis, in Chlamydomonas reinhardtii.

HEMA encodes glutamyl-tRNA reductase (GluTR), which catalyzes the first step specific for tetrapyrrole biosynthesis in plants, archaea, and most eubacteria. In higher plants, GluTR is feedback inhibited by heme and intermediates of chlorophyll biosynthesis. It plays a key role in controlling flux through the tetrapyrrole biosynthetic pathway. This enzyme, which in Chlamydomonas reinhardtii is encoded by a single gene (HEMA), exhibits homology to GluTRs of higher plants and cyanobacteria. HEMA mRNA accumulation was inducible not only by light but also by treatment of dark-adapted cells with Mg-protoporphyrin IX (MgProto) or hemin. The specificity of these tetrapyrroles as inducers was demonstrated by the absence of induction observed upon the feeding of protoporphyrin IX, the precursor of both heme and MgProto, or chlorophyllide. The HEMA mRNA accumulation following treatment of cells with light and hemin was accompanied by increased amounts of GluTR. However, the feeding of MgProto did not suggest a role for Mg-tetrapyrroles in posttranscriptional regulation. The induction by light but not that by the tetrapyrroles was prevented by inhibition of cytoplasmic protein synthesis. Since MgProto is synthesized exclusively in plastids and heme is synthesized in plastids and mitochondria, the data suggest a role of these compounds as organellar signals that control expression of the nuclear HEMA gene.

Aldehyde Oxidoreductases↗
PubMed1987

Inhibition of bacteriochlorophyll synthesis in Rhodobacter sphaeroides subsp. denitrificans grown in light under denitrifying conditions.

The inclusion of nitrate or nitrite in cultures of Rhodobacter spaeroides subsp. denitrificans grown heterotrophically in light depressed the formation of bacteriochlorophyll a. The pigment biosynthesis was inhibited at the stage of the reduction of chlorophyllide (chlorin) to bacteriochlorophyllide (tetrahydroporphyrin) since 3-hydroxyethylchlorophyllide a accumulated in the culture medium. The addition of exogenous 5-aminolevulinic acid to these cultures resulted in a complete restoration of bacteriochlorophyll synthesis accompanied by the accumulation of 3-vinylbacteriopheophorbide. This indicates that under these conditions bacteriochlorophyll was formed via an alternative route, in which the reduction of chlorins to tetrahydroporphyrins precedes modifications of the C-3 side chain. The multiple forms of 5-aminolevulinic acid synthase were purified from cells grown with and without nitrate. Antibodies against these proteins were raised in rabbits and used in enzyme-linked immunosorbent assays for various forms of 5-aminolevulinic acid synthase. In denitrifying cells, the amount and activity of fraction I of the enzyme was reduced by approximately 40 and 30%, respectively. Partly active enzymes from both types of cells were activated by cystine trisulfide.

5-Aminolevulinate Synthetase↗
PubMed1990

Rhodobacter capsulatus genes involved in early steps of the bacteriochlorophyll biosynthetic pathway.

Three open reading frames in the Rhodobacter capsulatus photosynthesis gene cluster, designated F0, F108, and F1025, were disrupted by site-directed mutagenesis. Mutants bearing insertions in these reading frames were defective in converting protoporphyrin IX to magnesium-protoporphyrin monomethyl ester, protochlorophyllide to chlorophyllide a, and magnesium-protoporphyrin monomethyl ester to protochlorophyllide, respectively. These results demonstrate that the genes examined most likely encode enzyme subunits that catalyze steps common to plant and bacterial tetrapyrrole photopigment biosynthetic pathways. The open reading frames were found to be part of a large 11-kilobase operon that encodes numerous genes involved in early steps of the bacteriochlorophyll a biosynthetic pathway.

Amino Acid Sequence↗
PubMed2000

NADPH:Protochlorophyllide oxidoreductase uses the general import route into chloroplasts.

Chloroplast differentiation in angiosperm plants depends on the light-dependent conversion of protochlorophyllide to chlorophyllide by NADPH:protochlorophyllide oxidoreductase (PORA; EC 1.6.99.1), a nuclearly encoded protein. The protein import of the precursor form of PORA into plastids was shown previously to strictly depend on the presence of its substrate protochlorophyllide. PORA seemed to follow a novel, posttranslationally regulated import route. Here we demonstrate that the precursor of PORA from barley is imported into isolated barley plastids independently of protochlorophyllide. PORA as well as PORB import is competed for by the precursor of the small subunit of Rubisco. The data demonstrate that the PORA precursor uses the general import pathway into plastids. Furthermore, en route into chloroplasts the pea POR precursor can be cross-linked to the protein import channel in the outer envelope Toc75 from pea.

Aminolevulinic Acid↗
PubMedDate not supplied

Effects of enhanced UV-B on pigment-based phytoplankton biomass and composition of mesocosm-enclosed natural marine communities from three latitudes.

A series of three outdoor mesocosm experiments was undertaken in Rimouski (Canada), Ubatuba (Brazil) and Ushuaia (southern Argentina) to examine the effects of lamp-enhanced UV-B (280-320 nm) on phytoplankton communities isolated from seawater at each site. Detailed pigment composition was used to identify these communities. Each experiment compared three replicated UV-B treatments, consisting of natural sunlight conditions (NUVB), low-level UV-B enhancement corresponding to local 30% ozone depletion (LUVB) and high-level enhancement corresponding to 60% ozone depletion (HUVB). Each mesocosm (ca 2 m deep) was mixed continuously (turnover time, ca 1.3 h) and samples were obtained daily over 7-10 days. In Rimouski a large diatom bloom occurred during the first week. Repeated-measures analysis of variance (RM-ANOVA), with time as the repeated factor, showed slight but statistically significant increases in the chlorophyll (Chl) a level with the HUVB treatment, which were especially obvious over the last 3 days of the experiment. A large decrease in grazers (ciliates) that was observed concurrently with this treatment is the most likely explanation for the increase in Chl a level. The lack of negative effect on algal biomass by enhanced UV-B is attributed to the mixing inside the mesocosms and to the relatively low UV-B penetration. In Ubatuba levels of most pigments decreased over time, particularly fucoxanthin, Chl c3 and alloxanthin. The RM-ANOVA showed no effect of the UV-B treatments, except for Chl c3, which had significantly lower concentrations under natural UVB conditions, indicating that enhanced UV-B directly or indirectly favored Chl c3 algae (likely prymnesiophytes). Although particulate organic carbon concentration was significantly larger during HUVB treatment than during the other treatments, Chl a was unaffected, suggesting that enhanced UV-B favored heterotrophs. Lack of algal growth during this experiment was attributed to low nutrient concentrations (which were the lowest of the three sites), high irradiances (which were the highest noon incident photosynthetically available radiation and UV of the three sites) and UV-B penetration down to the bottom of the mesocosms. In Ushuaia a small bloom took place over the first 5 days. The RM-ANOVA showed no overall effect of the UV-B treatments for any of the pigments examined but on the last 3 days of the experiment several green algae-type pigments, such as Chl b and siphonein, showed increased concentrations under the HUVB treatment. UV-B enhancement hence favored green algae, as seen from the stronger increase over time in the ratio of Chl b to Chl a associated with the HUVB treatment. UV-B enhancement also seemed to cause a slight decrease in physiological condition, because the relative concentration of chlorophyllide a and some pheophorbides that may be the product of dying algae increased during the HUVB treatments in Ubatuba and particularly in Ushuaia (where UV-B also penetrated to the bottom of mesocosms). For all three sites changes in phytoplankton biomass due to the UV-B treatments were minor, even though UV-B enhancement was important. This study indicates that effects of enhanced UV-B on the community structure of both phytoplankton and their grazers are potentially more important than effects on overall algal biomass.

Biomass↗
PubMed2004

Effects of acid and alkali on the light absorption, energy transfer and protein secondary structures of core antenna subunits CP43 and CP47 of photosystem II.

The effects of acid and alkali treatment on the light absorption, energy transfer and protein secondary structure of the photosystem II core antenna CP43 and CP47 of spinach were investigated by the absorption spectra, fluorescence emission spectra and circular dichroism spectra. It has been found that acid treatment caused the appearance of absorption characteristic of pheophytin a (Pheo a), whereas alkali treatment induced a new absorption peak at 642 nm. The energy transfer between beta-carotene and chlorophyll a (Chl a) in CP43 was easily disturbed by alkali, whereas in CP47 was readily affected by acid. As to the effects on the secondary structure of proteins in CP43 and CP47, effects of acid were far less than those of alkali. Both acid and alkali disturbed the microenvironment of Chl a and interfered exciton interaction between Chl a molecules. It was suggested that acid and alkali affect the light absorption, energy transfer and protein secondary structure of CP43 and CP47 in a different way. H+ can permeate into the internal space of alpha-helix, change Chl a into Pheo a and disturb the microenvironment of pigments without damaging the secondary structure of protein, whereas OH- can induce the protein unfolding at first, then saponify Chl a to chlorophyllide and disturb the microenvironment of pigments.

Acids↗
PubMed1998

Secreted, glycosylated arginase from Xanthoria parietina thallus induces loss of cytoplasmic material from Xanthoria photobionts.

A secreted, glycosylated arginase (lectin) from Xanthoria parietina thallus binds to the cell wall of Xanthoria photobiont when cell wall urease has previously been induced. The uptake of this secreted arginase by the algal cell without cell wall ligand for the lectin increases the concentration of algal putrescine and it is followed by an apparent loss of chlorophyll. However, neither chlorophyllase activity has been detected nor chlorophyllide concentration increases after loading the cells with putrescine. The loss of chlorophyll can be explained by the loss of algal protoplast resulting from the action of a putrescine-activated glucanase and the split of their membrane in an hypoosmotic medium. The loss and split of protoplasts have been shown by light and transmission electron microscopy.

Arginase↗
PubMedDate not supplied

[Relationship between chlorophyll concentration and the energy reaction between protochlorophyll and chlorophyll in mixed associations].

In the paper results are presented of investigation of protochlorophyll (PChl) and chlorophyll (Chl) mixed associations and of interaction between them within the polymer molecular complex, which forms in mixture of water-dioxane (1 : 4). The initial PChl concentration in all solutions was constant (CPChl = 1 . 10(-5) m/l), and Chl concentration varied from 1.10(-8) m/l up to 2.10(-5) m/l. It is shown that with the rise of Chl proportion in the mixed aggregate the rearrangement of both donor (PChl) and acceptor (Chl) components of complex takes place. The luminescence quenching of PChl and the sensitization of Chl emission in mixed pigment associates were investigated of different Chl levels and the evaluation of efficiency of intracomplex electronic excitation energy transfer, determined from quenching and sensibilization, was performed. Similar dependence of energy transfer effectiveness on Chl concentration, determined by the two above-mentioned methods shows that the excitation migration in an associate takes place without losses. An analysis of results permits to conclude that a small trapping efficiency of PChl excitation by the acceptor part of the complex may be connected with the existence of the prerelaxation reverse energy transfer from Chl to PChl in mixed pigment associates. On the basis of the obtained data a mechanism of energy transfer from protochlorophyllide to chlorophyllide in etiolated leaves and homogenates is discussed.

Binding Sites↗
PubMed1984

[Free stamp-graft autodermoplasty in the treatment of granulating wounds and ulcers].

A new stamp--graft method of free autodermoplasty was used in 36 out of 70 patients operated upon with using stamps only and their combination with pedicled graft or partly put secondary sutures. It proved to be as effective as all other modifications of stamps with different methods and gave better final results as compared with the known publications concerning possible healing of dermatome split grafts known to have wider prospects in the treatment of mainly great burn wounds. Stamps and grafts were found to be more resistant to harmful effects of bad granulation medium, more reliable in adaptation and healing and to be good stimulators of the natural reparative regeneration. The optimum conditions were created by local oxybarotherapy, hemotransfusion by heparin--treated blood or direct transfusions and by preventing a purulent reaction by the administration of chlorophyllid, sulfomylon and enzymes.

Anti-Infective Agents, Local↗
PubMedDate not supplied

[Molecular arrangement of protochlorophyll aggregated forms in solid films].

The conditions were found for the successive self-assembly of two protochlorophyll aggregated forms in solid films with absorption maxima at 647 (+/-1) nm (PChl 647) and 651 (+/-1) nm (PChl 651) and fluorescence maxima at 653-655 nm and 654-657 nm, respectively. These forms model the native photochemically active form of the precursor of chlorophyll (chlorophyllide) in plants (P650). The investigation of infrared spectra (in the region 1800-1600 cm-1), CD-spectra and fluorescence, carried out in this study, permitted in between the indicated forms to distinguish the type of the molecular arrangement of aggregated structures, PChl 647 is supposed to consist of unstable dimers formed without the participation of keto groups of the cyclopentanone rings, while the structure of PChl 651 includes the dimers to bind more firmly by the intermolecular bonds formed at the expense of keto groups and a central magnesium atom.

Chlorophyll↗
PubMed1982

Some properties of purified fractions from bean etioplast membranes.

Distribution of proteins, protochlorophyllide and photoactivity was studied in fractions obtained from bean etioplast membranes purified by linear or discontinuous sucrose density gradient centrifugation. The polypeptide pattern of two selected membrane fractions was examined by means of polyacrylamide gel electrophoresis. Both fractions contained the doublet of molecular weights 34.000-35.000 characteristic of NADPH-Protochlorophyllide oxido-reductase but differed by accompanying proteins. When both fractions were illuminated, protochlorophyllide was photoreduced in chlorophyllide fluorescing at 688 nm. During a subsequent 30 min. dark period, the emission peak shifted rapidly up to 678 nm in one of the fractions while it moved slowly to 683 nm in the other one. The possible occurrence of two phototransformable protochlorophyllide-complexes is discussed. Delta-aminolevulinic acid pretreatment of etiolated leaves led to an increase in the amount of proteins in the etioplast membranes.

Cell Fractionation↗
PubMed1982

Evidence for a light-independent protochlorophyllide reductase in green barley leaves.

Evidence is presented that normal light-grown barley plants continue to synthesise chlorophyll when transferred to total darkness. This implies the existence of a light-independent protochlorophyllide reductase in barley as well as the light-dependent enzyme (NADPH protochlorophyllide oxido-reductase) involved in the phototransformation of protochlorophyllide to chlorophyllide. This finding is consistent with an earlier observation by Popov and Dilova (1969) that dark grown barley develops the ability to synthesise chlorophyll in the dark, after several hours exposure to light. Popov and Dilova's findings with etiolated barley are confirmed.

Darkness↗
PubMed1981

[Isolation and properties of the pigment-protein complex (protochlorophyllide - holochrome) from etiolated leaves of corn sprouts].

A pigment -- protein complex was isolated from etiolated leaves of corn sprouts using treatment by the detergent Triton X-100, ultracentrifugation and gel-filtration. The complex has a molecular weight of 50000 and upon illumination can convert protochlorophyllide (Pchld) into chlorophyllide (Chld). The low temperature fluorescence spectra of dark preparations reveal maxima of Pchld 632 (photo-inactive form) and Pchld 653 (photo-active form). Upon illumination Pchld 653 is converted into Chld 685. The kinetics of the precursor photoconversion into Chld are coincident with those for photoconversion in native etiolated corn leaves. The complex is completely inactivated at a decrease of pH down to 6.5 or during incubation at high temperature (30 degrees).

Bacterial Proteins↗
PubMedDate not supplied

[Energy migration in a pigmented protochlorophyllide complex].

Data are analysed concerning energy migration between protochlorophyllide and chlorophyllide formed in etiolated leaves. It is found that phototransformation of the precursor proceeds in the pigment complexes similar to the multicentric photosynthetic unit. The complexes comprise no more than 26 molecules of the active form of protochlorophyllide P650 and two molecules of minor forms of P628 and P639 on the average with mean intermolecular distances 3 nm.

Chlorophyll↗