Terminal Oxidase (terminal + oxidase)

Distribution by Scientific Domains


Selected Abstracts


Control of chloroplast redox by the IMMUTANS terminal oxidase

PHYSIOLOGIA PLANTARUM, Issue 1 2004
Maneesha R. Aluru
Variegation mutants offer excellent opportunities to study interactions between the nucleus-cytoplasm, the chloroplast, and the mitochondrion. Variegation in the immutans (im) mutant of Arabidopsis is induced by a nuclear recessive gene and the extent of variegation can be modulated by light and temperature. Whereas the green sectors have morphologically normal chloroplasts, the white sectors are devoid of pigments and accumulate a colourless carotenoid, phytoene. The green sectors are hypothesized to arise from cells that have avoided irreversible photooxidative damage whereas the white sectors originate from cells that are photooxidized. Cloning of the IMMUTANS (IM) gene has revealed that IMMUTANS (IM) is a plastid homologue of the mitochondrial alternative oxidase. This finding suggested a model in which IM functions as a redox component of the phytoene desaturation pathway, which requires phytoene desaturase activity. Consistent with this idea, IM has quinol oxidase activity in vitro. Recent studies have revealed that IM plays a more global role in plastid metabolism. For example, it appears to be the elusive terminal oxidase of chlororespiration and also functions as a light stress protein. [source]


Stimulation of chlororespiration by heat and high light intensity in oat plants

PLANT CELL & ENVIRONMENT, Issue 8 2006
MARÍA JOSÉ QUILES
ABSTRACT High irradiance and moderate heat inhibit the activity of the photosynthetic apparatus of oat (Avena sativa L.) leaves. The incubation of oat leaves under high light intensity in conjunction with high temperatures strongly decreased the maximal quantum yield of photosystem (PS) II, indicating the close synergistic effect of both stress factors on PS II inhibition and the subsequent irreversible damage to the photosynthetic apparatus. The PS I A/B protein levels remained similar to control values in leaves incubated under high light intensity or moderate heat, and decreased only when both stress factors were simultaneously applied. Immunoblot analysis of thylakoid membranes using specific antibodies raised against the NDH-K subunit of the thylakoidal NADH dehydrogenase complex (NADH DH) and against plastid terminal oxidase (PTOX) revealed an increase in the amount of both proteins in response to high light intensity and/or heat treatments. In addition, these stress treatments were seen to stimulate the activity of electron donation by NADPH and ferredoxin to plastoquinone, the PTOX activity in plastoquinone oxidation and the NADH DH activity in thylakoid membranes. Incubation with n -propyl gallate (an inhibitor of PTOX) inhibited the increase of NDH-K and PTOX levels under high light intensity and heat, and slightly stimulated the activity of electron donation by NADPH and ferredoxin to plastoquinone. Antimycin A (an inhibitor of cyclic electron flow) increased the NADH DH activity and preserved the levels of NDH-K and PTOX in thylakoid membranes from leaves incubated under high light intensity and heat. The up-regulation of the PTOX and the thylakoidal NADH DH complex under these stress conditions supports a role for chlororespiration in the protection against high irradiance and moderate heat. [source]


Alternative Oxidase (AOX) Genes of African Trypanosomes: Phylogeny and Evolution of AOX and Plastid Terminal Oxidase Families

THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 4 2005
TAKASHI SUZUKI
Abstract. To clarify evolution and phylogenetic relationships of trypanosome alternative oxidase (AOX) molecules, AOX genes (cDNAs) of the African trypanosomes, Trypanosoma congolense and Trypanosoma evansi, were cloned by PCR. Both AOXs possess conserved consensus motifs (-E-, -EXXH-). The putative amino acid sequence of the AOX of T. evansi was exactly the same as that of T. brucei. A protein phylogeny of trypanosome AOXs revealed that three genetically and pathogenically distinct strains of T. congolense are closely related to each other. When all known AOX sequences collected from current databases were analyzed, the common ancestor of these three Trypanosoma species shared a sister-group position to T. brucei/T. evansi. Monophyly of Trypanosoma spp. was clearly supported (100% bootstrap value) with Trypanosoma vivax placed at the most basal position of the Trypanosoma clade. Monophyly of other eukaryotic lineages, terrestrial plants + red algae, Metazoa, diatoms, Alveolata, oomycetes, green algae, and Fungi, was reconstructed in the best AOX tree obtained from maximum likelihood analysis, although some of these clades were not strongly supported. The terrestrial plants + red algae clade showed the closest affinity with an ,-proteobacterium, Novosphingobium aromaticivorans, and the common ancestor of these lineages, was separated from other eukaryotes. Although the root of the AOX subtree was not clearly determined, subsequent phylogenetic analysis of the composite tree for AOX and plastid terminal oxidase (PTOX) demonstrated that PTOX and related cyanobacterial sequences are of a monophyletic origin and their common ancestor is linked to AOX sequences. [source]


Trypanosome Alternative Oxidase is Regulated Post-transcriptionally at the Level of RNA Stability

THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 4 2002
MINU CHAUDHURI
ABSTRACT In the bloodstream form of African trypanosomes, trypanosome alternative oxidase (TAO), the non-cytochrome ubiquinol:oxidoreductase, is the only terminal oxidase of the mitochondrial electron transport system. TAO is developmentally regulated during mitochondrial biogenesis in this parasite. During in vitro differentiation of Trypanosoma bmcei from the bloodstream to the procyclic form, the overall rate of oxygen consumption decreased about 80%. The mode of respiration changed over a 2- to 3-wk period from a cyanide-insensitive, SHAM-sensitive pathway to a predominantly cyanide-sensitive pathway. The TAO protein level gradually decreased to the level present in the procyclic forms during this 3-wk period. However, within the first week of differentiation, the TAO transcript level decreased about 90% and then in the following weeks it reached the level present in the established procyclic form, that is about 20% of that in bloodstream forms. Like other trypanosomatid genes TAO transcript synthesis remains unaltered in fully differentiated bloodstream and procyclic trypanosomes. The half-life of the TAO mRNA was about 3.2 h in the procyclic trypanosomes, whereas the TAO transcript level remained unaltered even after 4 h of incubation with actinomycin D in bloodstream forms. Inhibition of protein synthesis resulted in about a four-fold accumulation of the TAO transcript in the procyclic trypanosomes, comparable to the level present in the bloodstream forms. Thus, TAO is regulated at the level of mRNA stability and de novo protein synthesis is required for the reduction of the TAO mRNA pool in the procyclic form. [source]


Crystallization and preliminary crystallographic analysis of cyanide-insensitive alternative oxidase from Trypanosoma brucei brucei

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2010
Yasutoshi Kido
Cyanide-insensitive alternative oxidase (AOX) is a mitochondrial membrane protein and a non-proton-pumping ubiquinol oxidase that catalyzes the four-electron reduction of dioxygen to water. In the African trypanosomes, trypanosome alternative oxidase (TAO) functions as a cytochrome-independent terminal oxidase that is essential for survival in the mammalian host; hence, the enzyme is considered to be a promising drug target for the treatment of trypanosomiasis. In the present study, recombinant TAO (rTAO) overexpressed in haem-deficient Escherichia coli was purified and crystallized at 293,K by the hanging-drop vapour-diffusion method using polyethylene glycol 400 as a precipitant. X-ray diffraction data were collected at 100,K and were processed to 2.9,Å resolution with 93.1% completeness and an overall Rmerge of 9.5%. The TAO crystals belonged to the orthorhombic space group I222 or I212121, with unit-cell parameters a = 63.11, b = 136.44, c = 223.06,Å. Assuming the presence of two rTAO molecules in the asymmetric unit (2 × 38,kDa), the calculated Matthews coefficient (VM) was 3.2,Å3,Da,1, which corresponds to a solvent content of 61.0%. This is the first report of a crystal of the membrane-bound diiron proteins, which include AOXs. [source]


Regulation of expression of terminal oxidases in Paracoccus denitrificans

FEBS JOURNAL, Issue 8 2001
Marijke F. Otten
In order to study the induction of terminal oxidases in Paracoccus denitrificans, their promoters were fused to the lacZ reporter gene and analysed in the wild-type strain, in an FnrP-negative mutant, in a cytochrome bc1 -negative mutant, and in six single or double oxidase-negative mutant strains. The strains were grown under aerobic, semi-aerobic, and denitrifying conditions. The oxygen-sensing transcriptional-regulatory protein FnrP negatively regulated the activity of the qox promoter, which controls expression of the ba3 -type quinol oxidase, while it positively regulated the activity of the cco promoter, which controls expression of the cbb3 -type cytochrome c oxidase. The ctaDII and ctaC promoters, which control the expression of the aa3 -type cytochrome c oxidase subunits I and II, respectively, were not regulated by FnrP. The activities of the latter two promoters, however, did decrease with decreasing oxygen concentrations in the growth medium, suggesting that an additional oxygen-sensing mechanism exists that regulates transcription of ctaDII and ctaC. Apparently, the intracellular oxygen concentration (as sensed by FnrP) was not the only signal to which the oxidase promoters responded. At given extracellular oxygen status, both the qox and the cco promoters responded to mutations in terminal oxidase genes, whereas the ctaDII and ctaC promoters did not. The change of electron distribution through the respiratory network, resulting from elimination of one or more oxidase genes, may have changed intracellular signals that affect the activities of the qox and cco promoters. On the other hand, the re-routing of electron distribution in the respiratory mutants hardly affected the oxygen consumption rate as compared to that of the wild-type. This suggests that the mutants adapted their respiratory network in such a way that they were able to consume oxygen at a rate similar to that of the wild-type strain. [source]


Kinetics of leaf oxygen uptake represent in planta activities of respiratory electron transport and terminal oxidases

PHYSIOLOGIA PLANTARUM, Issue 1 2007
Agu Laisk
We present, for the first time, the oxygen response kinetics of mitochondrial respiration measured in intact leaves (sunflower and aspen). Low O2 concentrations in N2 (9,1500 ppm) were preset in a flow-through gas exchange measurement system, and the decrease in O2 concentration and the increase in CO2 concentration as result of leaf respiration were measured by a zirconium cell O2 analyser and infrared-absorption CO2 analyser, respectively. The low O2 concentrations little influenced the rate of CO2 evolution during the 60-s exposure. The initial slope of the O2 uptake curve on the dissolved O2 concentration basis was relatively constant in leaves of a single species, 1.5 mm s,1 in sunflower and 1.8 mm s,1 in aspen. The apparent K0.5(O2) values ranged from 0.33 to 0.67 ,M in sunflower and from 0.33 to 1.1 ,M in aspen, mainly because of the variation of the maximum rate, Vmax (leaf temperature 22°C). The initial slope of the O2 response of respiration characterizes the catalytic efficiency of terminal oxidases, an important parameter of the respiratory machinery in leaves. The plateau of the response characterizes the activity of the mitochondrial electron transport chain and is subject to regulations in accordance with the necessity for ATP production. The relatively low oxygen conductivity of terminal oxidases means that in leaves, less than 10% of the photosynthetic oxygen can be reassimilated by mitochondria. [source]


Cancer type-specific tNOX isoforms: A putative family of redox protein splice variants with cancer diagnostic and prognostic potential

BIOFACTORS, Issue 3 2008
D. James Morré
A proteomics approach with detection on western blots using an S-peptide tagged pan-tNOX (ENOX2) recombinant (scFv) antibody followed by alkaline phosphatase-linked anti S has revealed a family of more than 20 ENOX2 isoforms of varying molecular weights (34 to 94 kDa) and mostly of low isoelectric points (4.6 ± 0.7) based on serum analysis. Different isoforms characterize cancers of different tissue origins indicative of both cancer presence and tissue site of origin. ENOX2 proteins are cancer-associated and differ from constitutive (CNOX or ENOX1) proteins primarily by the absence of a drug binding site to which the cancer-specific scFv is directed. All are located on the cell surface where they function both as terminal oxidases for plasma membrane electron transport and carry out protein disulfide-thiol interchange. These proteins are shed into the blood and can also be found in urine. The tNOX isoform technology is under development as a clinical aid to identify unknown or uncertain primary cancers, evaluation of metastatic spread in post surgery patients, monitoring remission following cessation of therapy and for early diagnosis in at-risk populations. [source]