Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.3.5.1 (succinate dehydrogenase)
8,177 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report a structural characterization by electron microscopy and image analysis of a supramolecular complex consisting of photosystem I and light-harvesting complex I from the unicellular green alga Chlamydomonas reinhardtii. The complex is a monomer, has longest dimensions of 21.3 and 18.2 nm in projection, and is significantly larger than the corresponding complex in spinach. Comparison with photosystem I complexes from other organisms suggests that the complex contains about 14 light-harvesting proteins, two or three of which bind at the side of the PSI-H subunit. We suggest that special light-harvesting I proteins play a role in the binding of phosphorylated light-harvesting complex II in state 2.
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PMID:Supramolecular organization of photosystem I and light-harvesting complex I in Chlamydomonas reinhardtii. 1216 73

Xanthophylls participate in light harvesting and are essential in protecting the chloroplast from photooxidative damage. To investigate the roles of xanthophylls in photoprotection, we isolated and characterized extragenic suppressors of the npq1 lor1 double mutant of Chlamydomonas reinhardtii, which lacks zeaxanthin and lutein and undergoes irreversible photooxidative bleaching and cell death at moderate to high light intensities. Here, we describe three suppressor strains that carry point mutations in the coding sequence of the zeaxanthin epoxidase gene, resulting in the constitutive accumulation of zeaxanthin in a range of concentrations. The presence of zeaxanthin in these strains was sufficient to prevent photooxidative damage in the npq1 lor1 background. The size of the light-harvesting antenna in the suppressors decreased in high light in a manner that was proportional to the relative content of zeaxanthin, with the strain having the most zeaxanthin showing a severe reduction in levels of the major light-harvesting complex II proteins in high light. We show that the effect of constitutive zeaxanthin on light harvesting is not the main cause of increased photoprotection, because in the absence of zeaxanthin, a strain with a smaller light-harvesting antenna showed only minor protection against photobleaching in high light. Furthermore, the zeaxanthin-accumulating suppressors were able to tolerate higher levels of exogenous reactive oxygen than their parental strain under conditions that did not affect light harvesting. Our results are consistent with an antioxidant role of zeaxanthin in the quenching of singlet oxygen and/or free radicals in the thylakoid membrane in vivo.
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PMID:Zeaxanthin accumulation in the absence of a functional xanthophyll cycle protects Chlamydomonas reinhardtii from photooxidative stress. 1267 Oct 93

Photosynthetic activities were analyzed in Chlamydomonas reinhardtii mitochondrial mutants affected in different complexes (I, III, IV, I + III, and I + IV) of the respiratory chain. Oxygen evolution curves showed a positive relationship between the apparent yield of photosynthetic linear electron transport and the number of active proton-pumping sites in mitochondria. Although no significant alterations of the quantitative relationships between major photosynthetic complexes were found in the mutants, 77 K fluorescence spectra showed a preferential excitation of photosystem I (PSI) compared with wild type, which was indicative of a shift toward state 2. This effect was correlated with high levels of phosphorylation of light-harvesting complex II polypeptides, indicating the preferential association of light-harvesting complex II with PSI. The transition to state 1 occurred in untreated wild-type cells exposed to PSI light or in 3-(3,4-dichlorophenyl)-1,1-dimethylureatreated cells exposed to white light. In mutants of the cytochrome pathway and in double mutants, this transition was only observed in white light in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. This suggests higher rates of nonphotochemical plastoquinone reduction through the chlororespiratory pathway, which was confirmed by measurements of the complementary area above the fluorescence induction curve in dark-adapted cells. Photo-acoustic measurements of energy storage by PSI showed a stimulation of PSI-driven cyclic electron flow in the most affected mutants. The present results demonstrate that in C. reinhardtii mutants, permanent defects in the mitochondrial electron transport chain stabilize state 2, which favors cyclic over linear electron transport in the chloroplast.
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PMID:Photosynthesis and state transitions in mitochondrial mutants of Chlamydomonas reinhardtii affected in respiration. 1463 Sep 58

Reversible phosphorylation of chl a/b protein complex II (LHCII), the mobile light-harvesting antenna, regulates its association and energy transfer/dissipation to photosystem (PS) II or I (state transition). Excitation of LHCII induces conformational changes affecting the exposure of the phosphorylation site at the N-terminal domain to protein kinase(s) [Zer, H., et al. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 8277-8282; Zer, H., et al. (2003) Biochemistry 42, 728-738]. Thus, it was of interest to examine whether the pigment composition of LHCII affects the light-induced modulation of LHCII phosphorylation and state transition. To this end, we have used thylakoids of wild-type Chlamydomonas reinhardtii and xanthophyll deficient mutants npq1, lor1, npq2, npq1 lor1, and npq2 lor1. Phosphorylated protein bands P11, P13, and P17 are considered components of the mobile C. reinhardtii LHCII complex. The protein composition of these bands has been analyzed by mass spectrometry using Qtof-2 with a nanospray attachment. P11 and P13 contain C. reinhardtii light-harvesting chlorophyll a/b binding protein LhcII type I. P17 contains C. reinhardtii LhcII types III and IV. Illumination of isolated thylakoids inhibits the redox-controlled phosphorylation of polypeptide bands P13 and P17 and to a lower extent that of P11. The light-induced inhibition of LHCII phosphorylation and the state transition process are not influenced by extensive differences in the xanthophyll composition of the mutants. Thus, LHCII can be visualized as possessing two functionally distinct, independent domains: (i) the pigment binding transmembrane domain regulating the extent of energy transfer/dissipation and (ii) the surface-exposed phosphorylation site regulating the association of LHCII with PSII or PSI.
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PMID:Light-modulated exposure of the light-harvesting complex II (LHCII) to protein kinase(s) and state transition in Chlamydomonas reinhardtii xanthophyll mutants. 1519 25

We have addressed the functional and structural roles of three domains of the chloroplast Rieske iron-sulfur protein; that is, the flexible hinge that connects the transmembrane helix to the soluble cluster-bearing domain, the N-terminal stromal protruding domain, and the transmembrane helix. To this aim mutants were generated in the green alga Chlamydomonas reinhardtii. Their capacities to assemble the cytochrome b6f complex, perform plastoquinol oxidation, and signal redox-induced activation of the light-harvesting complex II kinase during state transition were tested in vivo. Deletion of one residue and extensions of up to five residues in the flexible hinge had no significant effect on complex accumulation or electron transfer efficiency. Deletion of three residues (Delta3G) dramatically decreased reaction rates by a factor of approximately 10. These data indicate that the chloroplast iron-sulfur protein-linking domain is much more flexible than that of its counterpart in mitochondria. Despite greatly slowed catalysis in the Delta3G mutant, there was no apparent delay in light-harvesting complex II kinase activation or state transitions. This indicates that conformational changes occurring in the Rieske protein did not represent a limiting step for kinase activation within the time scale tested. No phenotype could be associated with mutations in the N-terminal stromal-exposed domain. In contrast, the N17V mutation in the Rieske protein transmembrane helix resulted in a large decrease in the cytochrome f synthesis rate. This reveals that the Rieske protein transmembrane helix plays an active role in assembly-mediated control of cytochrome f synthesis. We propose a structural model to interpret this phenomenon based on the C. reinhardtii cytochrome b6f structure.
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PMID:The chloroplast Rieske iron-sulfur protein. At the crossroad of electron transport and signal transduction. 1531 16

State transition in photosynthesis is a short-term balancing mechanism of energy distribution between photosystem I (PSI) and photosystem II (PSII). When PSII is preferentially excited (state 2), a pool of mobile light-harvesting complex II (LHCII) antenna proteins is thought to migrate from PSII to PSI, but biochemical evidence for a physical association between LHCII proteins and PSI in state 2 is weak. Here, using the green alga Chlamydomonas reinhardtii, which has a high capacity for state transitions, we report the isolation of PSI-light-harvesting complex I (LHCI) super-complexes from cells locked into state 1 and state 2. We solubilized the thylakoid membranes with a mild detergent, separated the proteins by sucrose density gradient centrifugation, and subjected gradient fractions to gel-filtration chromatography. Three LHCII polypeptides were associated with a PSI-LHCI supercomplex only in state 2; we identified them as two minor monomeric LHCII proteins (CP26 and CP29) and one previously unreported major LHCII protein type II, or LhcbM5. These three LHCII proteins, in addition to the major trimeric LHCII proteins, were phosphorylated upon transition to state 2. The corresponding phylogenetic tree indicates that among the LHCII proteins associated with PSII, these three LHCII proteins are the most similar to the LHC proteins for PSI (LHCI). Our results are important because CP26, CP29, and LhcbM5, which have been viewed as belonging solely to the PSII complex, are now postulated to shuttle between PSI and PSII during state transitions, thereby acting as docking sites for the trimeric LHCII proteins in both PSI and PSII.
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PMID:Identification of the mobile light-harvesting complex II polypeptides for state transitions in Chlamydomonas reinhardtii. 1640 70

Partially purified intact chloroplasts were prepared from batch cultures of both wild type (Wt) and a mutant strain of Chlamydomonas reinhardtii. Protoplasts were generated from log phase cultures of Wt (137c) and the phosphoribulokinase-deficient mutant F60 by incubation of the cells in autolysine. These protoplasts were suspended in an osmoticum, cooled, and then subjected to a 40 pounds per square inch pressure shock using a Yeda pressure bomb. The resulting preparation was fractionated on a Percoll step gradient which separated the intact chloroplasts from both broken chloroplasts and protoplasts.The chloroplast preparation was not significantly contaminated with the cytoplasmic enzyme activity phosphoenolpyruvate carboxylase (>5%), and contained (100%) stromal enzyme activity ribulose-1,5-bisphosphate carboxylase. The chloroplast preparation is significantly contaminated by mitochondria, as determined by succinate dehydrogenase activity. Chloroplasts prepared from Wt cells retained CO(2)-dependent O(2) photoevolution at rates in excess of 60 micromoles per milligram chlorophyll per hour, an activity which is severely inhibited by the addition of 10 millimolar KH(2)PO(4). The chloroplasts are osmotically sensitive as determined by ferricyanide-dependent O(2) photoevolution.
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PMID:Partial Purification of Intact Chloroplasts from Chlamydomonas reinhardtii. 1666 33

A method for isolating intact chloroplasts from Chlamydomonas reinhardtii F-60 was developed from the Klein, Chen, Gibbs, Platt-Aloia procedure ([1983] Plant Physiol 72: 481-487). Protoplasts, generated by treatment with autolysine, were lysed with a solution of digitonin and fractionated on Percoll step gradients. The chloroplasts were assessed to be 90% intact (ferricyanide assay) and free from cytoplasmic contamination (NADP isocitrate dehydrogenase activity) and to range from 2 to 5% in mitochondrial contamination (cytochrome c oxidase activity). About 25% of the cellular succinate dehydrogenase activity (21.6 micromoles per milligram chlorophyll per hour, as determined enzymically) was placed within the chloroplast. Chloroplastic succinate dehydrogenase had a K(m) for succinate of 0.55 millimolar and was associated with the thylakoidal material derived from the intact chloroplasts. This same thylakoidal material, with an enzymic assay of 21.6 micromoles per milligram chlorophyll per hour was able to initiate a light-dependent uptake of oxygen at a rate of 16.4 micromoles per milligram chlorophyll per hour when supplied with succinate and methyl viologen. Malonate was an apparent competitive inhibitor of this reaction. The succinate dehydrogenase activity present in the chloroplast was sufficient to account for the photoanaerobic rate of acetate dissimilation in H(2) adapted Chlamydomonas (M Gibbs, RP Gfeller, C Chen [1986] Plant Physiol 82: 160-166).
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PMID:Evidence for Chloroplastic Succinate Dehydrogenase Participating in the Chloroplastic Respiratory and Photosynthetic Electron Transport Chains of Chlamydomonas reinhardtii. 1666 55

The localization of a series of enzymes involved in the anaerobic photodissimilation of acetate in Chlamydomonas reinhardtii F-60 adapted to a hydrogen metabolism was determined through the enzymic analyses of the chloroplastic, cytoplasmic, and mitochondrial fractions obtained with a cellular fractionation procedure that incorporated cell wall removal by treatment with autolysine, digestion of the plasmalemma with the detergent digitonin, and fractionation by differential centrifugation on a Percoll step gradient. The sequence of events leading to the photoevolution of H(2) from acetate includes the conversion of acetate into succinate via the extraplastidic glyoxylate cycle, the oxidation of succinate to fumarate by chloroplastic succinate dehydrogenase, and the oxidation of malate to oxaloacetate in the chloroplast by NAD dependent malate dehydrogenase. The level of potential activity for the enzymes assayed were sufficient to accommodate the observed rate of the photoanaerobic dissimilation of acetate and the photoevolution of H(2).
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PMID:Localization of the Enzymes Involved in the Photoevolution of H(2) from Acetate in Chlamydomonas reinhardtii. 1666 78

Mutants with defects in the cytochrome (cyt) b6/f complex were analyzed for their effect on the expression of a subgroup of nuclear genes encoding plastid-localized enzymes participating in chlorophyll biosynthesis. Their defects ranged from complete loss of the cytb6/f complex to point mutations affecting specifically the quinone-binding QO site. In these seven mutants, light induction of the tetrapyrrole biosynthetic genes was either abolished or strongly reduced. In contrast, a normal induction of chlorophyll biosynthesis genes was observed in mutants with defects in photosystem II, photosystem I, or plastocyanin, or in wild-type cells treated with 3-(3'4'-dichlorophenyl)-1,1-dimethylurea or 2,5-dibromo-3-methyl-6-isopropyl benzoquinone. We conclude that the redox state of the plastoquinone pool does not control light induction of these chlorophyll biosynthetic genes. The signal that affects expression of the nuclear genes appears to solely depend on the integrity of the cytb6/f complex QO site. Since light induction of these genes in Chlamydomonas has recently been shown to involve the blue light receptor phototropin, the results suggest that cytb6/f activity regulates a plastid-derived factor required for their expression. This signaling pathway differs from that which regulates state transitions, since mutant stt7, lacking a protein kinase involved in phosphorylation of the light-harvesting complex II, was not altered in the expression of the chlorophyll biosynthetic genes.
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PMID:Defects in the cytochrome b6/f complex prevent light-induced expression of nuclear genes involved in chlorophyll biosynthesis. 1667 22


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