Biosynthesis Of Photosynthetic Pigments Research Articles

Crystal structure of Pseudomonas fluorescens 4-hydroxyphenylpyruvate dioxygenase: an enzyme involved in the tyrosine degradation pathway.

In plants and photosynthetic bacteria, the tyrosine degradation pathway is crucial because homogentisate, a tyrosine degradation product, is a precursor for the biosynthesis of photosynthetic pigments, such as quinones or tocophenols. Homogentisate biosynthesis includes a decarboxylation step, a dioxygenation and a rearrangement of the pyruvate sidechain. This complex reaction is carried out by a single enzyme, the 4-hydroxyphenylpyruvate dioxygenase (HPPD), a non-heme iron dependent enzyme that is active as a homotetramer in bacteria and as a homodimer in plants. Moreover, in humans, a HPPD deficiency is found to be related to tyrosinemia, a rare hereditary disorder of tyrosine catabolism. We report here the crystal structure of Pseudomonas fluorescens HPPD refined to 2.4 A resolution (Rfree 27.6%; R factor 21.9%). The general topology of the protein comprises two barrel-shaped domains and is similar to the structures of Pseudomonas 2,3-dihydroxybiphenyl dioxygenase (DHBD) and Pseudomonas putida catechol 2,3-dioxygenase (MPC). Each structural domain contains two repeated betaalpha betabeta betaalpha modules. There is one non-heme iron atom per monomer liganded to the sidechains of His161, His240, Glu322 and one acetate molecule. The analysis of the HPPD structure and its superposition with the structures of DHBD and MPC highlight some important differences in the active sites of these enzymes. These comparisons also suggest that the pyruvate part of the HPPD substrate (4-hydroxyphenylpyruvate) and the O2 molecule would occupy the three free coordination sites of the catalytic iron atom. This substrate-enzyme model will aid the design of new inhibitors of the homogentisate biosynthesis reaction.

Inhibition by glucose of chlorophyll a and phycocyanobilin biosynthesis in the unicellular red alga Galdieria partita at the stage of coproporphyrinogen III formation

The repression effect of d-glucose on the pigment apparatus of photosynthesis in the unicellular acidophilic red alga Galdieria partita capable of heterotrophic growth was studied. The rate of cell growth under heterotrophic conditions was higher by more than one order of magnitude than that in the autotrophic ones, and the size of those cells was larger. The addition of 1% d-glucose to the growth medium caused an increase in the number of mitochondrion profiles in the cell and a decline of thylakoid number in the chloroplast of G. partita. The loss of thylakoid membranes is accompanied by a reduction of the contents of chlorophyll a. C-phycocyanin and allophycocyanin in the heterotrophic cells. Simultaneously, switching G. partita from autotrophic growth to heterotrophic nutrition led to the excretion of coproporphyrin(ogen) III into the growth medium. Thus, the presence of d-glucose caused a reduction of pigment contents in the cell, due to the inhibition of chlorophyll a and phycocyanobilin biosynthesis at the stage of the transformation of their universal precursor, coproporphyrinogen III, to protoporphyrinogen IX. In the mixotrophic culture of G. partita light induces both the biosynthesis of photosynthetic pigments and the excretion of coproporphyrin(ogen) III. It is supposed that light affects an earlier stage in the biosynthetic pathway of chlorophyll a and phycocyanobilin than does d-glucose.

Влияние экзогенных нативных и модифицированных нуклеиновых кислот на биосинтез фотосинтетических пигментов у Nicotiana tabacum L. 1. Содержание хлорофиллов и каротиноидов у растений первого поколения

Влияние экзогенных нативных и модифицированных нуклеиновых кислот на биосинтез фотосинтетических пигментов у Nicotiana tabacum L. 1. Содержание хлорофиллов и каротиноидов у растений первого поколения

The influence of exogenously supplied spermine on protochlorophyllide and chlorophyll biosynthesis

The pigment mutant C-2A′ of the unicellular green alga Scenedesmus obliquus synthesizes only protochlorophyllide and traces of chlorophyll in darkness. The reduction of protochlorophyllide to chlorophyllide and the synthesis of chlorophyll take place in the light. The tetramine spermine, contrary to the diamine putrescine and the triamine spermidine, regulates the amount of protochlorophyllide and chlorophyll in the dark and in the light. Low amounts of exogenous spermine induce chlorophyll biosynthesis (the optimum level is 0.32 mM SPM), while higher amounts inhibit chlorophyll biosynthesis. In the dark, spermine enhances the amount of accumulated protochlorophyllide, a fact that we attribute to inhibition of the light-independent protochlorophyllide oxidoreductase activity. Uptake measurements of spermine and its possible incorporation in prolamellar bodies/prothylakoids in comparison with the influence of spermine on chlorophyll biosynthesis allowed us to determine approximately and to discuss the likely role of spermine in the biosynthesis of photosynthetic pigments.

Mapping and sequencing of an actively transcribed Euglena gracilis chloroplast gene ( ccsA) homologous to the Arabidopsis thaliana nuclear gene cs(ch-42)

We mapped and sequenced a novel chloroplast gene encoding a protein (348 amino acids) which shows a high sequence identity with both the decoded nuclear cs(ch-42) gene product of Arabidopsis thaliana, and the C-terminal half of the decoded ‘ crtA’ gene product of Rhodobacter capsulatus. The chloroplast gene ( ccsA) is split (two exons) and transcribed into a stable mRNA of about 1200 nucleotides. The putative protein may be involved in the biosynthesis of photosynthetic pigments.

Transformation of glutamate to delta-aminolevulinic acid by soluble extracts of Synechocystis sp. PCC 6803 and other oxygenic prokaryotes.

delta-Aminolevulinic acid is the first committed precursor in the biosynthesis of hemes, phycobilins, and chlorophylls. Plants and algae synthesize delta-aminolevulinic acid from glutamate via an RNA-dependent 5-carbon pathway. Previous reports demonstrated that cyanobacteria form delta-aminolevulinic acid from glutamate in vivo. We now report the direct measurement of this activity in vitro. Three oxygenic prokaryotes were examined, the unicellular cyanobacteria Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 7002 (Agmenellum quadruplicatum PR-6) and the chlorophyll a- and b-containing filamentous prochlorophyte Prochlorothrix hollandica. delta-Aminolevulinic acid-forming activity was detected in soluble extracts of all three species. delta-Aminolevulinic acid formation by Synechocystis extracts was further characterized. Activity depended upon addition of reduced pyridine nucleotide, ATP, and Mg2+ to the incubation mixture. NADPH was a more effective pyridine nucleotide than NADH at low concentrations, but NADPH inhibited delta-amino-levulinic acid formation above 1 mM, whereas NADH did not. The pH optimum was about 7.6, and the ATP concentration optimum was 0.1 mM. Activity was stimulated by addition of RNA derived from Synechocystis or Chlorella, and abolished by preincubation with RNase A. After RNase inactivation, activity was restored by addition of RNasin to block further RNase action, followed by supplementation with Synechocystis RNA. Activity was inhibited by micromolar concentrations of hemin, as was previously found with plant and algal extracts. Complete dependence on added glutamate could not be achieved. Radioactivity was incorporated into delta-aminolevulinic acid when the incubation mixture contained 1-[14C]glutamate. Activity in the Synechocystis enzyme extract was stimulated by the addition of a partially purified enzyme fraction from Chlorella. It thus appears that prokaryotic oxygenic organisms share with chloroplasts the capacity for biosynthesis of photosynthetic pigments from glutamate via the RNA-dependent 5-carbon pathway.

Ferrochelatase activity in the photosynthetic alga Cyanidium caldarium. Development of the enzyme during biosynthesis of photosynthetic pigments.

Dark-grown cells of the photosynthetic alga Cyanidium caldarium were shown to contain ferrochelatase activity, which increased markedly when the cells were induced to form pigments by exposure to light. Km values for the crude enzyme preparation were 14.8 microM and 6.5 microM for binding of Co2+ and deuteroporphyrin IX respectively.

Effect of the Herbicide San 6706 on Biosynthesis of Photosynthetic Pigments and Prenylquinones in Raphanus and in Hordeum Seedlings

The pyridazinone herbicide San 6706 blocks chlorophyll and carotenoid formation simultaneously in a correlated way in both Raphanus and Hordeum seedlings. With decreasing carotenoid content the carotenoid precursor phytoene appears in San 6706-treated plants. The accumulation of the chloroplast prenylquinones (plastoquinone-9, α-tocopherol, α-tocoquinone and vitamin K1) is much less affected. This indicates that the biosynthesis of C20- and C45-prenyl chains (geranyl-geraniol, phytol and solanesol) which are incorporated in prenylquinones is not blocked by San 6706. It is assumed that the block of chlorophyll and carotenoid formation is due to one basic inhibition mechanism. The possibility that San 6706 may interfere with chloroplast ribosome formation, is discussed.

O-Methylthreonine, a new bleaching agent for Euglena gracilis.

SUMMARY: O-Methylthreonine (OM) inhibits multiplication and photosynthetic pigment synthesis in Euglena gracilis and Ochromonas danica; it does not inhibit Chlamydomonas reinhardi or Rhodopseudomonas palustris. Inhibition of multiplication and pigment synthesis may be prevented by l-isoleucine. OM also causes the permanent loss of chlorophyll and appreciable loss of carotenoids in E. gracilis and this may be prevented by l-isoleucine, α-aminobutyric acid, α-ketobutyric acid, l-threonine, l-homoserine, or l-methionine. α-Ketobutyric acid is most effective on a molar basis and is therefore postulated to be the target of OM inhibition. Isoleucine plays a role in the biosynthesis of photosynthetic pigments and lipids in Euglena gracilis, for the incorporation of 14C-l-isoleucine radioactivity into both the pigments and lipids is markedly diminished by bleaching agents which prevent pigment synthesis without affecting multiplication, i.e. O-methylthreonine or streptomycin. When pigment synthesis is blocked amino acids accumulate in the culture supernate.