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:1.9.3.1 (cytochrome oxidase)
8,822 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The complete nucleotide sequence of the Chlamydomonas eugametos (Chlamydomonadales, Chlorophyceae, sensu Mattox and Stewart) mitochondrial genome has been determined (22,897 bp, 34.6% G + C). The genes identified in this circular-mapping genome include those for apocytochrome b, subunit 1 of the cytochrome oxidase complex, subunits 1, 2, 4, 5, and 6 of the NADH dehydrogenase complex, discontinuous large and small subunit ribosomal rRNAs and three tRNAs whose anticodons CAU, CCA and UUG are specific for methionine, tryptophan and glutamine, respectively. The C. eugametos mitochondrial DNA (mtDNA), therefore, shares almost the same reduced set of coding functions and similar unusual features of rRNA gene organization with the linear 15.8 kb mtDNA of Chlamydomonas reinhardtii, the only other completely sequenced chlamydomonadalean mtDNA. However, sequence analysis of the C. eugametos mtDNA has revealed the following distinguishing features relative to those of C. reinhardtii: (1) the absence of a reverse transcriptase-like gene homologue, (2) the presence of an additional gene for tRNA(met) that may be a pseudogene, (3) a completely different gene order, (4) transcription of all genes from the same mtDNA strand, (5) a lower G + C content, (6) less pronounced bias in codon usage, and (7) nine group I introns, several of which contain open reading frames coding for potential maturases/endonucleases and two have a nucleotide at the 5' or 3' splice site of the deduced precursor RNAs that deviates from highly conserved nucleotides reported in other group I introns. The features of mitochondrial genome organization and gene content shared by C. eugametos and C. reinhardtii contrast with those of other green algal mtDNAs that have been characterized in detail. The deep evolutionary divergence between these two Chlamydomonas taxa within the Chlamydomonadales suggests that their shared features of mitochondrial genome organization evolved prior to the origin of this group.
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PMID:Complete sequence of the mitochondrial DNA of Chlamydomonas eugametos. 948 40

The 22,704-bp circular mitochondrial DNA (mtDNA) of the chlamydomonad alga Chlorogonium elongatum was completely cloned and sequenced. The genome encodes seven proteins of the respiratory electron transport chain, subunit 1 of the cytochrome oxidase complex (cox1), apocytochrome b (cob), five subunits of the NADH dehydrogenase complex (nad1, nad2, nad4, nad5, and nad6), a set of three tRNAs (Q, W, M), and the large (LSU)- and small (SSU)-subunit ribosomal RNAs. Six group-I introns were found, two each in the cox1, cob, and nad5 genes. In each intron an open reading frame (ORF) related to maturases or endonucleases was identified. Both the LSU and the SSU rRNA genes are split into fragments intermingled with each other and with other genes. Although the average A + T content is 62.2%, GC-rich clusters were detected in intergenic regions, in variable domains of the rRNA genes, and in introns and intron-encoded ORFs. A comparison of the genome maps reveals that C. elongatum and Chlamydomonas eugametos mtDNAs are more closely related to one another than either is to Chlamydomonas reinhardtii mtDNA.
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PMID:The mitochondrial genome of Chlorogonium elongatum inferred from the complete sequence. 976 88

We have investigated a light-conditional mutant of Chlamydomonas reinhardtii (J12) that is unable to synthesize chlorophyll in the dark with the aim of characterizing the mitochondrial membrane polypeptides of this alga. A crude membrane fraction derived from etiolated cells was analyzed by gel electrophoresis, immunoblot analysis, and pulse-labeling in the presence of specific protein synthesis inhibitors. This fraction contained both mitochondrial and etioplast membranes, and the latter contained appreciable amounts of subunits of the cytochrome b6f complex. The mitochondria-encoded subunit 1 of cytochrome-c oxidase called COX1 was identified, and its synthesis was detected in this membrane fraction. The redox-difference spectra of mitochondrial cytochromes were studied in whole cells and membrane fractions, in both respiratory-competent and -deficient strains. Mitochondrial membranes could be further purified after sucrose gradient centrifugation. The use of etiolated cells and their membrane extracts, in association with appropriate methodologies, opens ways to study the molecular genetics of mitochondria in C. reinhardtii and allows us to address the question of the cooperation established between the three genetic compartments of a plant cell.
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PMID:Etiolated cells of Chlamydomonas reinhardtii: choice material for characterization of mitochondrial membrane polypeptides. 1160 85

Chlamydomonas reinhardtii cultures, deprived of inorganic sulfur, undergo dramatic changes during adaptation to the nutrient stress [Biotechnol. Bioeng. 78 (2002) 731]. When the capacity for Photosystem II (PSII) O(2) evolution decreases below that of respiration, the culture becomes anaerobic [Plant Physiol. 122 (2000) 127]. We demonstrate that (a) the photochemical activity of PSII, monitored by in situ fluorescence, also decreases slowly during the aerobic period; (b) at the exact time of anaerobiosis, the remaining PSII activity is rapidly down regulated; and (c) electron transfer from PSII to PSI abruptly decreases at that point. Shortly thereafter, the PSII photochemical activity is partially restored, and H(2) production starts. Hydrogen production, which lasts for 3-4 days, is catalyzed by an anaerobically induced, reversible hydrogenase. While most of the reductants used directly for H(2) gas photoproduction come from water, the remaining electrons must come from endogenous substrate degradation through the NAD(P)H plastoquinone (PQ) oxido-reductase pathway. We propose that the induced hydrogenase activity provides a sink for electrons in the absence of other alternative pathways, and its operation allows the partial oxidation of intermediate photosynthetic carriers, including the PQ pool, between PSII and PSI. We conclude that the reduced state of this pool, which controls PSII photochemical activity, is one of the main factors regulating H(2) production under sulfur-deprived conditions. Residual O(2) evolved under these conditions is probably consumed mostly by the aerobic oxidation of storage products linked to mitochondrial respiratory processes involving both the cytochrome oxidase and the alternative oxidase. These functions maintain the intracellular anaerobic conditions required to keep the hydrogenase enzyme in the active, induced form.
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PMID:The dependence of algal H2 production on Photosystem II and O2 consumption activities in sulfur-deprived Chlamydomonas reinhardtii cells. 1467 Jun 5

Compelling evidence exists that the colorless algae of the genus Polytomella arose from a green Chlamydomonas-like ancestor by losing its functional photosynthetic apparatus. Due to the close relationship between the colorless and the green chlorophyte, Polytomella sp. appeared as a useful indicative framework for structural studies of Chlamydomonas reinhardtii mitochondria. However, comparative studies reported here unexpectedly revealed significant differences between the mitochondrial respiratory systems of the two algae. Two-dimensional blue native/SDS-PAGE of isolated mitochondria indicated that cytochrome-containing respiratory complexes III and IV in the two chlorophytes contrast in size, subunit composition and relative abundance. Complex IV in Polytomella is smaller than its counterpart in C. reinhardtii and occurs in two forms that differ presumably in the presence of subunit COXIII. The cytochrome c and the iron-sulfur Rieske protein of both chlorophytes revealed structural differences on the amino acid sequence level. Under comparable culture conditions, the colorless alga exhibits lower levels of cytochrome c and complex IV but a higher respiratory activity than the green alga. Cytochrome c levels were also found to be differently regulated by the growth conditions in both algae. The divergence between the respiratory systems in the two related chlorophytes can be viewed as a consequence of the loss of photosynthetic activity and/or of the adaptation to the environment via the acquisition of a more flexible, heterotrophic metabolism. Our understanding of mitochondrial function and evolution is expected to be greatly enhanced via further parallel studies of photosynthetic/non-photosynthetic algae, for which this study forms an incentive.
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PMID:Divergence of the mitochondrial electron transport chains from the green alga Chlamydomonas reinhardtii and its colorless close relative Polytomella sp. 1594 81

The cleavable pre-sequences of imported chloroplast and mitochondrial proteins have several features in common. This structural similarity prompted us to test whether a chloroplast pre-sequence (;transit peptide') can also be decoded by the mitochondrial import machinery. In the green alga, Chlamydomonas reinhardtii, the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) (a chloroplast protein) is nuclear-encoded and synthesized in the cytosol with a transient pre-sequence of 45 residues. The 31 amino-terminal residues of this chloroplast pre-sequence were fused to mouse dihydrofolate reductase (a cytosolic protein) and to yeast cytochrome oxidase subunit IV (an imported mitochondrial protein) from which the authentic pre-sequence had been removed. The chloroplast pre-sequence transported both attached proteins into the yeast mitochondrial matrix or inner membrane, although it functioned less efficiently than an authentic mitochondrial pre-sequence. We conclude that mitochondrial and chloroplast pre-sequences perform their function by a similar mechanism.
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PMID:The cleavable pre-sequence of an imported chloroplast protein directs attached polypeptides into yeast mitochondria. 1645 86

The possibility that glycolate oxidation in unicellular green algae is linked to mitochondrial electron transport, rather than to peroxisomal metabolism as in higher plants and animals, was studied in a mutant of Chlamydomonas reinhardtii (dk97) deficient in cytochrome oxidase. This mutant had normal rates of dark respiration (40 +/- 15 mumol of O(2) uptake per hr per mg of chlorophyll) but had only 11% of wild-type levels of cytochrome oxidase activity. Salicylhydroxamic acid (SHAM) reduced the dark respiration rate of dk97 cells by 71%, but cyanide did not significantly inhibit this rate. During photosynthesis in the presence of SHAM, glycolate oxidation was blocked, resulting in glycolate accumulation and excretion by mutant cells but not by wild-type Chlamydomonas. D-Lactate, which accumulated after brief periods of anaerobiosis in Chlamydomonas, was reoxidized by air-grown cells only aerobically in the light, and reoxidation of D-lactate was blocked by SHAM in the dk97 cells. Thus, glycolate and D-lactate dehydrogenase activities are both linked to mitochondrial electron transport in Chlamydomonas. During photosynthetic (14)CO(2) fixation by dk97 cells in the presence of SHAM, (14)C-labeled tricarboxylic acid cycle intermediates accumulated, indicating that, in Chlamydomonas, mitochondrial respiration functions during photosynthesis.
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PMID:Inhibition of glycolate and D-lactate metabolism in a Chlamydomonas reinhardtii mutant deficient in mitochondrial respiration. 1657

Inhibitor titration curves and discrimination against (18)O(2) by mitochondrial respiration in three strains of green algae (Selenastrum minutum [Naeg.] Collins, and two strains of Chlamydomonas reinhardtii Dangeard) with differing respiratory capabilities were determined. Discrimination for cytochrome pathway respiration ranged from 19.89 to 20.43%. Discrimination for alternative pathway respiration by wild-type C. reinhardtii (measured in the presence of KCN) was 25.46%, while discrimination values for a cytochrome oxidase deficient mutant of C. reinhardtii ranged from 24.24 to 24.96%. In the absence of KCN, the alternative pathway was not engaged in wild-type C. reinhardtii, the only algal strain that possessed both cytochrome and alternative pathway capacities.
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PMID:Cytochrome and alternative pathway respiration in green algae : measurements using inhibitors and o(2) discrimination. 1666 62

Mass spectrometric analysis of gas exchange in light and dark by N-limited cells of Chlamydomonas reinhardtii indicated that ammonium assimilation was accompanied by an increase in respiratory carbon flow to provide carbon skeletons for amino acid synthesis. Tricarboxylic acid (TCA) cycle carbon flow was maintained by the oxidation of TCA cycle reductant via the mitochondrial electron transport chain. In wild-type cells, inhibitor studies and (18)O(2) discrimination experiments indicated that respiratory electron flow was mediated entirely via the cytochrome pathway in both the light and dark, despite a large capacity for the alternative pathway. In a cytochrome oxidase deficient mutant, or in wild-type cells in the presence of cyanide, the alternative pathway could support the increase in TCA cycle carbon flow. These different mechanisms of oxidation of TCA cycle reductant were reflected by the much greater SHAM sensitivity of ammonium assimilation by cytochrome oxidase-deficient cells as compared to wild type.
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PMID:Cytochrome and Alternative Pathway Respiration during Transient Ammonium Assimilation by N-Limited Chlamydomonas reinhardtii. 1666 7

Photosynthetic organisms are among the earliest life forms on earth and their biochemistry is strictly dependent on a wide range of inorganic nutrients owing to the use of metal cofactor-dependent enzymes in photosynthesis, respiration, inorganic nitrogen and sulfur assimilation. Chlamydomonas reinhardtii is a photosynthetic eukaryotic model organism for the study of trace metal homeostasis. Chlamydomonas spp. are widely distributed and can be found in soil, glaciers, acid mines and sewage ponds, suggesting that the genus has significant capacity for acclimation to micronutrient availability. Analysis of the draft genome indicates that metal homeostasis mechanisms in Chlamydomonas represent a blend of mechanisms operating in animals, plants and microbes. A combination of classical genetics, differential expression and genomic analysis has led to the identification of homologues of components known to operate in fungi and animals (e.g., Fox1, Ftr1, Fre1, Fer1, Ctr1/2) as well as novel molecules involved in copper and iron nutrition (Crr1, Fea1/2). Besides activating iron assimilation pathways, iron-deficient Chlamydomonas cells re-adjust metabolism by reducing light delivery to photosystem I (to avoid photo-oxidative damage resulting from compromised FeS clusters) and by modifying the ferredoxin profile (perhaps to accommodate preferential allocation of reducing equivalents). Up-regulation of a MnSOD isoform may compensate for loss of FeSOD. Ferritin could function to buffer the iron released from programmed degradation of iron-containing enzymes in the chloroplast. Some metabolic adjustments are made in anticipation of deficiency while others occur only with sustained or severe deficiency. Copper-deficient Chlamydomonas cells induce a copper assimilation pathway consisting of a cell surface reductase and a Cu(+) transporter (presumed CTR homologue). There are metabolic adaptations in addition: the synthesis of "back-up" enzymes for plastocyanin in photosynthesis and the ferroxidase in iron assimilation plus activation of alternative oxidase to handle the electron "overflow" resulting from reduced cytochrome oxidase function. Oxygen-dependent enzymes in the tetrapyrrole pathway (coproporphyrinogen oxidase and aerobic oxidative cyclase) are also increased in expression and activity by as much as 10-fold but the connection between copper nutrition and tetrapyrroles is not understood. The copper-deficiency responses are mediated by copper response elements that are defined by a GTAC core sequence and a novel metalloregulator, Crr1, which uses a zinc-dependent SBP domain to bind to the CuRE. The Chlamydomonas model is ideal for future investigation of nutritional manganese deficiency and selenoenzyme function. It is also suited for studies of trace nutrient interactions, nutrition-dependent metabolic changes, the relationship between photo-oxidative stress and metal homeostasis, and the important questions of differential allocation of limiting metal nutrients (e.g., to respiration vs. photosynthesis).
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PMID:Between a rock and a hard place: trace element nutrition in Chlamydomonas. 1676 55


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