Disease relevance of Plastoquinone

• Chlorophyll fluorescence analysis shows that in vivo the Ndh complex catalyses the post-illumination reduction of the plastoquinone pool and in the light optimizes the induction of photosynthesis under conditions of water stress [1].
• Highly divergent methyltransferases catalyze a conserved reaction in tocopherol and plastoquinone synthesis in cyanobacteria and photosynthetic eukaryotes [2].
• Obligate photoheterotrophic mutants of the cyanobacterium Synechocystis sp. PCC 6803 that carry deletions of conserved residues in the plastoquinone-binding niche of the D1 protein were used to select for spontaneous mutations that restore photoautotrophic growth [3].
• Recruitment of a foreign quinone into the A1 site of photosystem I. Characterization of a menB rubA double deletion mutant in Synechococcus sp. PCC 7002 devoid of FX, FA, and FB and containing plastoquinone or exchanged 9,10-anthraquinone [4].
• The chloroplast Ndh complex mediates the dark reduction of the plastoquinone pool in response to heat stress in tobacco leaves [5].

High impact information on Plastoquinone

• It is hypothesized that this heme, exposed to the cavity and a neighboring plastoquinone and close to the positive surface potential of the complex, can function in cyclic electron transport via anionic ferredoxin [6].
• PGR5 encodes a novel thylakoid membrane protein that is involved in the transfer of electrons from ferredoxin to plastoquinone [7].
• The inactive LHC II-kinase system could not be reactivated in vitro either by light or by reduction of the plastoquinone pool following addition of reduced duroquinone (TMQH2) [8].
• The presence of the photosystem II centers is then not required for the occurrence of the plastoquinone-mediated phosphorylation of light-harvesting complex polypeptides [9].
• Measurements of photosynthetic parameters and the use of electron transport inhibitors indicated that a novel signal transduction pathway was initiated at plastoquinone and regulated, at least in part, by the redox status of the plastoquinone pool [10].

Chemical compound and disease context of Plastoquinone

• Our results indicate that in Synechocystis in contrast to the situation in higher plants the 4-hydroxyphenylpyruvate dioxygenase is not required for the synthesis of plastoquinone [11].
• For the Synechococcus enzyme, competition between norflurazon and NADP, as well as plastoquinone, could be demonstrated [12].

Biological context of Plastoquinone

• Changes in binding of herbicides and QB to D1 as a result of the mutations revealed specific interactions between amino acid residues in D1 and the plastoquinone and distinguished between the binding sites of QB and herbicides [13].
• On the basis of these experimental results, we propose a model for a light intensity signaling system where cab gene expression is reversibly repressed by a phosphorylated factor coupled to the redox status of plastoquinone through a chloroplast protein kinase [14].
• Flash-induced kinetics of the redox changes of Cyt b and of the formation of a transmembrane potential have been measured in Chlorella sorokiniana cells incubated in reducing conditions that induce a full reduction of the plastoquinone pool [15].
• Three pseudorevertants isolated from the delta YNIV246-9 mutant contained a duplication (7-15 codons) of the DNA sequence immediately downstream of the deletion; the protein region encoded by this DNA may include part of the putative de helix, an important constituent of the plastoquinone-binding niche [3].
• The apg1 plants lacked plastoquinone (PQ), suggesting that the APG1 protein is involved in the methylation step of PQ biosynthesis, which is localized at the envelope membrane [16].

Anatomical context of Plastoquinone

• Biosynthesis of ubiquinone and plastoquinone in the endoplasmic reticulum-Golgi membranes of spinach leaves [17].
• Polypeptides encoded by plastid ndh genes form a complex (Ndh) which could reduce plastoquinone with NADH [18].
• The Ndh complex is a homologue of complex I of mitochondria and eubacteria and is considered to be a plastoquinone reductase [19].
• Studies using various inhibitors indicate that the HL response is not mediated by the redox state of plastoquinone pool or reactive oxygen species, but required de novo protein synthesis in the cytosol [20].
• The measurements of diphenylhexatriene (DPH) and trimethylammonium diphenylhexatriene (TMA-DPH) fluorescence anisotropy in egg yolk lecithin (EYL) and of DPH anisotropy in dipalmitoylphosphatidylcholine (DPPC) liposomes containing different concentrations of oxidized and reduced ubiquinone (UQ) and plastoquinone (PQ) homologues have been performed [21].

Associations of Plastoquinone with other chemical compounds

• We propose a model for carotenoid synthesis in photosynthetic tissue whereby plastoquinone acts as an intermediate electron carrier between carotenoid desaturases and the photosynthetic electron transport chain [22].
• The permanent structural coupling between plastoglobules and thylakoid membranes suggests that the lipid molecules contained in the plastoglobule cores (carotenoids, plastoquinone, and tocopherol [vitamin E]) are in a dynamic equilibrium with those located in the thylakoid membranes [23].
• The activation of the kinase after incubation of dark-adapted thylakoids at pH 4.3 coincides with an increase in the plastoquinol: plastoquinone ratio up to 0.25 [24].
• Detailed characterization of the preparation demonstrated a fully active electron transport chain from the manganese cluster to plastoquinone in the Q(B) binding site [25].
• A detergent-containing system was reconstructed with thylakoid Ndh complex and peroxidase which oxidized NADH with H(2)O(2) in a plastoquinone-dependent process [18].

Gene context of Plastoquinone

• Mutation of the PDS1 locus disrupts the activity of p-hydroxyphenylpyruvate dioxygenase (HPPDase), the first committed step in the synthesis of both plastoquinone and tocopherols in plants [26].
• The thylakoid membranes of most photosynthetic organisms contain a terminal oxidase (PTOX, the product of the Arabidopsis IMMUTANS gene) that functions in the oxidation of the plastoquinone pool [27].
• These data indicate that NR is activated by the oxidized state of an electron transport component located after the plastoquinone pool [28].
• In addition, disruption of Synechocystis sp. PCC 6803 HPT function causes an absence of tocopherols without affecting plastoquinone-9 levels, indicating that separate polyprenyltransferases exist for tocopherol and plastoquinone synthesis in Synechocystis sp. PCC 6803 [29].
• The methyltransferase encoded by the gene sll0418 is not essential either for tocopherol or plastoquinone synthesis [30].

Analytical, diagnostic and therapeutic context of Plastoquinone

• Genetic dissection of carotenoid synthesis in arabidopsis defines plastoquinone as an essential component of phytoene desaturation [22].
• A time-resolved FTIR difference study of the plastoquinone QA and redox-active tyrosine YZ interactions in photosystem II [31].
• The plastoquinone content of photosystem II complexes isolated from spinach photosystem II-enriched membranes subjected to strong photoinhibitory illumination under anaerobic conditions was determined by HPLC [32].
• Using redox titrations, it is shown here that the optimal activity lies in the range of the midpoint potential of the plastoquinone/plastohydroquinone redox couple [33].

References