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PubMed1995

Purification and two-dimensional crystallization of bacterial cytochrome oxidases.

A novel strategy which employes chromatography on an immobilized metal ion has been developed for the purification of bacterial cytochrome c and quinol oxidases. Many bacterial oxidase complexes appear to have a natural affinity to bind to the chelated copper ion. A combination of three different chromatographic principles (anion exchange, metal-affinity and gel filtration) makes an effective tool chest for the preparation of homogeneous and protein-chemically pure bacterial oxidases. These preparations have been used for two-dimensional crystallization. Until now, crystals have been obtained using the Paracococcus denitrificans and Rhodobacter sphaeroides cytochrome aa3 and the Escherichia coli cytochrome bo. The crystals diffract to approximately 2.5 nm in negative stain and have potential for further structural studies.

Bacteria↗
PubMed1995

Import of the cytochrome oxidase subunit Va precursor into yeast mitochondria is mediated by the outer membrane receptor Mas20p.

Post-translational import of precursor proteins into yeast mitochondria is mediated by at least four protease-sensitive outer membrane proteins: Mas20p, Mas22p, Mas37p, and Mas70p. These "import receptors" recognize either the N-terminal targeting signal or some other feature of mitochondrial precursor proteins. The only exception to this general rule appeared to be the precursor to subunit Va of cytochrome c oxidase (COXVa). Although this precursor carries a typical N-terminal mitochondrial targeting sequence, its import into mitochondria has been suggested to be independent of the known import receptors. Here we show that if import into isolated yeast mitochondria is assayed under conditions in which binding of the COXVa precursor to mitochondria is rate-limiting, import is strongly inhibited by protease pretreatment of the mitochondria or by antibodies against Mas20p. Post-translational import of the COXVa precursor can thus proceed by the general, receptor-mediated pathway.

Biological Transport↗
PubMed1986

Paramecium mitochondrial DNA sequences and RNA transcripts for cytochrome oxidase subunit I, URF1, and three ORFs adjacent to the replication origin.

A 2-kb region adjacent to the replication origin (ori) and a 3-kb region located between the small and large ribosomal RNAs of Paramecium mitochondrial (mt) DNA have been sequenced and the locations of their transcripts determined. The ori segment contains four transcripts, some of which are overlapping, which encode a known protein and two other open reading frames. The other segment encodes, on separate transcripts, the cytochrome c oxidase subunit one gene (COI) and the URF1 gene (ND1) common to most mt genomes. All these genes have the same orientation and do not contain introns. The COI gene is the most divergent of those known and has an internal 108 amino acid 'insert' not found in COI genes from other organisms. With these data it is possible to define a probable Paramecium mt genetic code. With the exception that TGA codes for tryptophan and the use of different start codons, Paramecium mtDNA appears to follow the universal code. GTA possibly can be used as a start codon.

Amino Acid Sequence↗
PubMed1990

Evidence for a functional cytoplasmic domain of phagocyte oxidase cytochrome b558.

Cytoplasmic domains of transmembrane proteins play a critical role in cellular processes involving interactions between membrane and cytosolic components. Activation of the phagocytic cell respiratory burst oxidase, the electron transport chain responsible for superoxide anion (O2-.) production, requires membrane components including cytochrome b558 and several cytosolic proteins; but the biochemical interactions of these components are poorly understood. Cytochrome b558 is an electron transport component of the oxidase. A role for cytochrome b558 in the organization or integration of other oxidase components has also been hypothesized. Antibodies binding the cytoplasmic carboxyl-terminal tail of the transmembrane 91-kDa subunit of cytochrome b558 specifically inhibited an amphiphile-activated cell-free O2-.-generating system that requires neutrophil membranes and cytosol. Synthetic peptides encompassing a 7-amino acid carboxyl-terminal sequence (RGVHFIF) within the same region of the 91-kDa subunit blocked activation of the oxidase by arachidonate, but did not affect activity of the assembled oxidase when added after arachidonate to the cell-free O2-.-generating system. The same peptides inhibited activation of the respiratory burst when allowed to diffuse into electrically permeabilized neutrophils before stimulation with formyl-methionyl-leucyl-phenylalanine or phorbol myristate acetate. These studies define a functional cytoplasmic domain of the transmembrane 91-kDa subunit of cytochrome b558 which may mediate interactions with other cellular proteins essential to activation of the phagocyte respiratory burst.

Amino Acid Sequence↗
PubMed2001

Linear aspects of changes in deoxygenated hemoglobin concentration and cytochrome oxidase oxidation during brain activation.

We used near infrared spectroscopy (NIRS) to investigate the vascular and metabolic response to brain activation in human primary and adjacent secondary visual cortex. NIRS is able to measure concentration changes in deoxygenated hemoglobin ([deoxy-Hb]) (which mainly contribute to the blood oxygenation level-dependent (BOLD) signal in functional magnetic resonance imaging (fMRI)) as well as concentration changes of oxygenated hemoglobin ([oxy-Hb]) and corpuscular blood volume ([total-Hb] = [oxy-Hb] + [deoxy-Hb]) and changes in the redox status of the cytochrome c oxidase ([Cyt-Ox]), a putative parameter for cellular oxygenation. A sound understanding of the transfer functions between stimulus parameters, neuronal activity, and vascular/metabolic parameters is important for interpretation of data acquired with indirect neuroimaging techniques like fMRI, especially in event-related design studies. In the present study we tested whether the vascular/metabolic response to stimulation can be described as a linear and time invariant system. Since linearity is a property attributed to systems that satisfy the scaling and superposition properties, as a first simple test, superposition of the responses obtained from short duration visual stimuli was used to predict the responses of longer duration stimuli. Our results showed that the predictions of [deoxy-Hb] and [Cyt-Ox] responses to stimuli of 6- to 24-s duration were satisfactory whereas predictions of [oxy-Hb] and [total-Hb] were insufficient. In a second step, a calculated convolution function of an assumed impulse response function and the stimulus function was fitted with the measured [deoxy-Hb] and [Cyt-Ox] curves to obtain amplitude, time delay, and time constant parameters. We show that predictions of cellular and vascular oxygenation responses to visual stimulation are good for 6- to 24-s stimuli duration under the assumption of a linear transfer characteristic. This model is not valid for corpuscular volume changes which affect mainly the [oxy-Hb] response. Noninvasive NIRS is shown to be a suitable method to get more direct information about neuronal-activity-associated changes in cerebral parameters which are partly reflected in BOLD signal but are not fully understood yet.

Adult↗
PubMed2006

Mitochondrial cytochrome oxidase produces nitric oxide under hypoxic conditions: implications for oxygen sensing and hypoxic signaling in eukaryotes.

Eukaryotic cells respond to low-oxygen concentrations by upregulating hypoxic nuclear genes (hypoxic signaling). Although it has been shown previously that the mitochondrial respiratory chain is required for hypoxic signaling, its underlying role in this process has been unclear. Here, we find that yeast and rat liver mitochondria produce nitric oxide (NO) at dissolved oxygen concentrations below 20 microM. This NO production is nitrite (NO2-) dependent, requires an electron donor, and is carried out by cytochrome c oxidase in a pH-dependent fashion. Mitochondrial NO production in yeast is influenced by the YHb flavohemoglobin NO oxidoreductase, stimulates expression of the hypoxic nuclear gene CYC7, and is accompanied by an increase in protein tyrosine nitration. These findings demonstrate an alternative role for the mitochondrial respiratory chain under hypoxic or anoxic conditions and suggest that mitochondrially produced NO is involved in hypoxic signaling, possibly via a pathway that involves protein tyrosine nitration.

Animals↗
PubMed1982

The cytochrome oxidase subunit I split gene in Saccharomyces cerevisiae: genetic and physical studies of the mtDNA segment encompassing the 'cytochrome b-homologous' intron.

We have constructed a refined genetic and physical map of 38 oxi3 mutations. With the help of the rho- clones derived from 'short' and 'long' genes, pairwise crosses between mutants, estimations of their reversion frequencies and analyses of mitochondrially synthesized proteins, we have characterized and localized several mutants in the exon A4 and in the intron aI4. We present genetic and physical evidence that in the 'long' gene the exon A5 is split into at least three quite distinct exons, A5-1, A5-2 and A5-3 where numerous mutations are localized. We suggest that a novel 56 Kd polypeptide, which accumulates in some cis-dominant oxi3- mutants results from the translation of the upstream exons and the downstream aI4 intron.

Base Sequence↗