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Further observations on the Mg-protoporphyrin IX monomethyl ester (oxidative) cyclase system.

ABSTRACT: The Mg-protoporphyrin IX monomethyl ester (oxidative) cyclase was strongly inhibited by CN- and N3- in a reconstituted system, but was inhibited slightly or not at all by the same reagents in intact developing chloroplasts. Known inhibitors of cytochrome P-450 processes showed no consistent effect. Benzoquinone and quinol, which can give rise to the same semiquinone by one-electron redox events, were strong inhibitors of the cyclase. It was previously shown that O2 and a source of electrons are required in the cyclization process. The substrates for the dehydrogenases of the pentose phosphate pathway (glucose 6-phosphate and 6-phosphogluconate) were effective reductants in the reconstituted system with supernatant that had been dialysed or passed through Sephadex G-50, in the absence of added NADP+. However, inhibitor studies suggested that the electrons from these sugar phosphates reached the cyclase system via NADPH. Therefore we infer the presence of protein-bound NADP+ that can be reduced by glucose 6-phosphate and 6-phosphogluconate and donate reducing equivalents to the cyclase system. This bound NADPH pool may be particularly effective in the cyclization process, owing to channeling. These findings are discussed in relation to the results of a companion paper [Whyte and Castelfranco (1993) Biochem. J. 290, 361-367] on the breakdown of chloroplast pigments in the same reconstituted system.

SUBMITTER: Whyte BJ

PROVIDER: S-EPMC1132280 | biostudies-other | 1993 Mar

REPOSITORIES: biostudies-other

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Mutation in Mg-Protoporphyrin IX Monomethyl Ester Cyclase Decreases Photosynthesis Capacity in Rice.

Project description:In photosynthesis, the pigments chlorophyll a/b absorb light energy to convert to chemical energy in chloroplasts. Though most enzymes of chlorophyll biosynthesis from glutamyl-tRNA to chlorophyll a/b have been identified, the exact composition and regulation of the multimeric enzyme Mg-protoporphyrin IX monomethyl ester cyclase (MPEC) is largely unknown. In this study, we isolated a rice pale-green leaf mutant m167 with yellow-green leaf phenotype across the whole lifespan. Chlorophyll content decreases 43-51% and the granal stacks of chloroplasts becomes thinner in m167. Chlorophyll fluorescence parameters, including Fv/Fm (the maximum quantum efficiency of PSII) and quantum yield of PSII (Y(II)), were lower in m167 than those in wild type plants (WT), and photosynthesis rate decreases 40% in leaves of m167 mutant compared with WT plants, which lead to yield reduction in m167. Genetic analysis revealed that yellow-green leaf phenotype of m167 is controlled by a single recessive genetic locus. By positional cloning, a single mutated locus, G286A (Alanine 96 to Threonine in protein), was found in the coding sequence of LOC_Os01g17170 (Rice Copper Response Defect 1, OsCRD1), encoding a putative subunit of MPEC. Expression profile analysis demonstrated that OsCRD1 is mainly expressed in green tissues of rice. Sequence alignment analysis of CRD1 indicated that Alanine 96 is very conserved in all green plants and photosynthetic bacteria. OsCRD1 protein mainly locates in chloroplast and the point mutation A96T in OsCRD1 does not change its location. Therefore, Alanine96 of OsCRD1 might be fundamental for MPEC activity, mutation of which leads to deficiency in chlorophyll biosynthesis and chloroplast development and decreases photosynthetic capacity in rice.

| S-EPMC5271374 | biostudies-literature

Synthesis of divinyl protochlorophyllide. Enzymological properties of the Mg-protoporphyrin IX monomethyl ester oxidative cyclase system.

Project description:The resolution and reconstitution of the Mg-protoporphyrin IX monomethyl ester oxidative cyclase system into a supernatant and a pellet fraction was accomplished by a procedure involving salt treatment followed by osmotic shock. Recombination of pellet and supernatant fractions was required for cyclase activity. This restoration effect could be demonstrated using either Mg-protoporphyrin IX or Mg-protoporphyrin IX monomethyl ester as the cyclase substrate in the presence or absence of S-adenosylmethionine. Pretreatment of the pellet fraction with either 8-hydroxyquinoline or desferal mesylate inhibited cyclase activity, indicating that there is a heavy-metal-ion requirement in this fraction. The cyclase supernatant protein(s) was not internalized by Sephadex G-50 and did not bind to Blue Sepharose, suggesting that it has a molecular mass of over 30 kDa and that it does not bind the cofactor NADPH. The cyclase supernatant protein did bind to MgProtoMe2-bound Sepharose and could be eluted by raising the pH to 9.7 in the presence of 4 mM-n-octyl glucoside. The pH optimum of the cyclase was 9.0. About a 40-fold purification of the cyclase supernatant protein was achieved by a combination of (NH4)2SO4 fractionation and phenyl-Sepharose chromatography.

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Xantha-l encodes a membrane subunit of the aerobic Mg-protoporphyrin IX monomethyl ester cyclase involved in chlorophyll biosynthesis.

Project description:Chlorophyll biosynthesis is a process involving approximately 20 different enzymatic steps. Half of these steps are common to the biosynthesis of other tetrapyrroles, such as heme. One of the least understood enzymatic steps is formation of the isocyclic ring, which is a characteristic feature of all (bacterio)chlorophyll molecules. In chloroplasts, formation of the isocyclic ring is an aerobic reaction catalyzed by Mg-protoporphyrin IX monomethyl ester cyclase. An in vitro assay for the aerobic cyclase reaction required membrane-bound and soluble components from the chloroplasts. Extracts from barley (Hordeum vulgare L.) mutants at the Xantha-l and Viridis-k loci showed no cyclase activity. Fractionation of isolated plastids by Percoll gradient centrifugation showed that xantha-l and viridis-k mutants are defective in components associated with chloroplast membranes. The Xantha-l gene, corresponding to Arabidopsis thaliana CHL27, Rubrivivax gelatinosus acsF, Chlamydomonas reinhardtii CRD1, and CTH1 and situated at the short arm of barley chromosome 3 (3H), was cloned, and the mutations in xantha-l(35), xantha-l(81), and xantha-l(82) were characterized. This finding connected biochemical and genetic data because it demonstrated that Xantha-l encodes a membrane-bound cyclase subunit. The evidence suggests that the aerobic cyclase requires at least one soluble and two membrane-bound components.

| S-EPMC556314 | biostudies-literature

Yellow-Leaf 1 encodes a magnesium-protoporphyrin IX monomethyl ester cyclase, involved in chlorophyll biosynthesis in rice (Oryza sativa L.)

Project description:We performed a transcriptomics analysis in the wild type and the mutant, and the expression levels of photosynthesis and chloroplast development genes were affected in yl-1 mutant.

2017-06-29 | GSE96073 | GEO

How the O<sub>2</sub>-dependent Mg-protoporphyrin monomethyl ester cyclase forms the fifth ring of chlorophylls.

Project description:Mg-protoporphyrin IX monomethyl ester (MgPME) cyclase catalyses the formation of the isocyclic ring, producing protochlorophyllide a and contributing substantially to the absorption properties of chlorophylls and bacteriochlorophylls. The O2-dependent cyclase is found in both oxygenic phototrophs and some purple bacteria. We overproduced the simplest form of the cyclase, AcsF, from Rubrivivax gelatinosus, in Escherichia coli. In biochemical assays the di-iron cluster within AcsF is reduced by ferredoxin furnished by NADPH and ferredoxin:NADP+ reductase, or by direct coupling to Photosystem I photochemistry, linking cyclase to the photosynthetic electron transport chain. Kinetic analyses yielded a turnover number of 0.9 min-1, a Michaelis-Menten constant of 7.0 µM for MgPME and a dissociation constant for MgPME of 0.16 µM. Mass spectrometry identified 131-hydroxy-MgPME and 131-keto-MgPME as cyclase reaction intermediates, revealing the steps that form the isocyclic ring and completing the work originated by Sam Granick in 1950.

| S-EPMC7610348 | biostudies-literature

Yellow-Leaf 1 encodes a magnesium-protoporphyrin IX monomethyl ester cyclase, involved in chlorophyll biosynthesis in rice (Oryza sativa L.).

Project description:Magnesium-protoporphyrin IX monomethyl ester cyclase (MPEC) catalyzes the conversion of MPME to divinyl protochlorophyllide (DVpchlide). This is an essential enzyme during chlorophyll (Chl) biosynthesis but details of its function in rice are still lacking. Here, we identified a novel rice mutant yellow-leaf 1 (yl-1), which showed decreased Chl accumulation, abnormal chloroplast ultrastructure and attenuated photosynthetic activity. Map-based cloning and over-expression analysis suggested that YL-1 encodes a subunit of MPEC. The YL-1 protein localizes in chloroplasts, and it is mainly expressed in green tissues, with greatest abundance in leaves and young panicles. Results of qRT-PCR showed that Chl biosynthesis upstream genes were highly expressed in the yl-1 mutant, while downstream genes were compromised, indicating that YL-1 plays a pivotal role in the Chl biosynthesis. Furthermore, the expression levels of photosynthesis and chloroplast development genes were also affected. RNA-seq results futher proved that numerous membrane-associated genes, including many plastid membrane-associated genes, have altered expression pattern in the yl-1 mutant, implying that YL-1 is required for plastid membrane stability. Thus, our study confirms a putative MPME cyclase as a novel key enzyme essential for Chl biosynthesis and chloroplast membrane stability in rice.

| S-EPMC5448749 | biostudies-literature

Identification of a Mg-protoporphyrin IX monomethyl ester cyclase homologue, EaZIP, differentially expressed in variegated Epipremnum aureum 'Golden Pothos' is achieved through a unique method of comparative study using tissue regenerated plants.

Project description:Variegated plants provide a valuable tool for studying chloroplast biogenesis by allowing direct comparison between green and white/yellow sectors within the same leaf. While variegated plants are abundant in nature, the mechanism of leaf variegation remains largely unknown. Current studies are limited to a few mutants in model plant species, and are complicated by the potential for cross-contamination during dissection of leaf tissue into contrasting sectors. To overcome these obstacles, an alternative approach was explored using tissue-culture techniques to regenerate plantlets from unique sectors. Stable green and pale yellow plants were developed from a naturally variegated Epipremnum aureum 'Golden Pothos'. By comparing the gene expression between green and pale yellow plants using suppression subtractive hybridization in conjunction with homologous sequence search, nine down-regulated and 18 up-regulated genes were identified in pale yellow plants. Transcript abundance for EaZIP (Epipremnum aureum leucine zipper), a nuclear gene homologue of tobacco NTZIP and Arabidopsis CHL27, was reduced more than 4000-fold in qRT-PCR analysis. EaZIP encodes the Mg-protoporphyrin IX monomethyl ester cyclase, one of the key enzymes in the chlorophyll biosynthesis pathway. Examination of EaZIP expression in naturally variegated 'Golden Pothos' confirmed that EaZIP transcript levels were correlated with leaf chlorophyll contents, suggesting that this gene plays a major role in the loss of chlorophyll in the pale yellow sectors of E. aureum 'Golden Pothos'. This study further suggests that tissue-culture regeneration of plantlets from different coloured sectors of variegated leaves can be used to investigate the underlying mechanisms of variegation.

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Mg-Protoporphyrin IX Signals Enhance Plant's Tolerance to Cold Stress.

Project description:The relationship between Mg-protoporphyrin IX (Mg-Proto IX) signals and plant's tolerance to cold stress is investigated. Arabidopsis seedlings grown for 3 weeks were pretreated with 2 mM glutamate (Glu) and 2 mM MgCl2 for 48 h at room temperature to induce Mg-Proto IX accumulation. Then cold stress was performed at 4°C for additional 72 h. Glu + MgCl2 pre-treatments alleviated the subsequent cold stress significantly by rising the leaf temperature through inducing Mg-Proto IX signals. The protective role of Glu + MgCl2 treatment was greatly compromised in the mutants of Mg-Proto IX synthesis, Mg-Proto IX signaling, and cyanide-resistant respiration. And the enhancement of cold-responsive gene expression was greatly compromised in the mutants of Mg-Proto IX synthesis, Mg-Proto IX signaling and ABA signaling, but not in the mutant of cyanide-resistant respiration. Cold stress promoted cyanide-resistant respiration and leaf total respiration exponentially, which could be further induced by the Glu + MgCl2 treatment. Mg-Proto IX signals also activate antioxidant enzymes and increase non-enzymatic antioxidants [glutathione but not ascorbic acid (AsA)] to maintain redox equilibrium during the cold stress.

| S-EPMC5068135 | biostudies-literature

MicroRNA156 (miR156) Negatively Impacts Mg-Protoporphyrin IX (Mg-Proto IX) Biosynthesis and Its Plastid-Nucleus Retrograde Signaling in Apple.

Project description:Plastid-nucleus retrograde signaling (PNRS) play essential roles in regulating nuclear gene expression during plant growth and development. Excessive reactive oxygen species can trigger PNRS. We previously reported that in apple (Malus domestica Borkh.) seedlings, the expression of microRNA156 (miR156) was significantly low in the adult phase, which was accompanied by high levels of hydrogen peroxide (H2O2) accumulation in chloroplasts. However, it was unclear whether adult-phase-specific chloroplast H2O2 may induce PNRS and affect miR156 expression, or miR156 triggers adult phase PNRS during the ontogenesis. In this paper, we examined the relationship between miR156 levels and six PNRS components in juvenile and adult phase leaves from 'Zisai Pearl'×'Red Fuji' hybrids. We found that PNRS generated by singlet oxygen (1O2), the photosynthetic redox state, methylerythritol cyclodiphosphate (MEcPP), SAL1-3-phosphoadenosine 5-phosphate (PAP) and WHIRLY1 were not involved. The accumulation of Mg-protoporphyrin IX (Mg-Proto IX), the expression of the synthetic genes MdGUN5 and MdGUN6, and Mg-Proto IX PNRS related nuclear genes increased with ontogenesis. These changes were negatively correlated with miR156 expression. Manipulating Mg-Proto IX synthesis with 5-aminolevulinic acid (ALA) or gabaculine did not affect miR156 expression in vitro shoots. In contrast, modulating miR156 expression via MdGGT1 or MdMIR156a6 transgenesis led to changes in Mg-Proto IX contents and the corresponding gene expressions. It was concluded that the Mg-Proto IX PNRS was regulated downstream of miR156 regardless of adult-phase-specific plastid H2O2 accumulation. The findings may facilitate the understanding of the mechanism of ontogenesis in higher plants.

| S-EPMC7285031 | biostudies-literature

Protoporphyrin IX/Cobyrinate Derived Hybrids - Novel Activators of Soluble Guanylyl Cyclase.

Project description:A new cobyrinate/protoporphyrin IX molecular hybrids were prepared via CuAAC reaction. The synthesis involved selective preparation of cobyrinate and PpIX derived building blocks possessing respectively terminal alkyne and azide moieties followed by the CuOAc catalyzed cycloaddition reaction. Synthesized molecules activated soluble guanylyl cyclase showing strong linker length/activation dependence.

| S-EPMC3600653 | biostudies-literature

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