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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The expression of the X-CGD gene, which encodes the heavy-chain subunit of the phagocyte cytochrome b, was studied during induced myeloid differentiation of HL-60 cells. Incubation of the cells with a combined regimen of retinoic acid and dimethyl formamide resulted in granulocytic morphological differentiation and acquisition of nitroblue tetrazolium reduction, a measure of superoxide generation. During the 5-day course of induced differentiation, the levels of X-CGD mRNA transcripts rose 13-fold, with a 2-fold increase detectable within 3 h of exposure to retinoic acid. Relative transcription rates for the X-CGD gene, determined by nuclear runoff, increased two- to eightfold after 24 to 72 h of induced differentiation. However, the greater change in X-CGD mRNA levels than that in transcription rates implies the involvement of posttranscriptional regulation as well. Fractionation by centrifugal elutriation into phases of the cell cycle showed expression of X-CGD transcripts predominantly in G1 cells before induction and in all phases of the cell cycle 24 h after induction. Thus the rapid increase in X-CGD expression in induced cells reflects the acquisition of functional competence and not the concomitant cessation of proliferation or shift in cell cycle distribution.
Mol Cell Biol 1988 Jul
PMID:Expression of the X-CGD gene during induced differentiation of myeloid leukemia cell line HL-60. 316 93

The protonmotive cytochrome b protein of the mitochondrial bc1 respiratory chain complex contains two reactions centers, designated Qo and Qi, which can be distinguished by the effects of different inhibitors. The nucleotide sequences have been determined of the mitochondrial cytochrome b genes from a series of mouse cell mutants selected for increased inhibitor resistance. Each mutant contains a single nucleotide change which results in an amino acid substitution. When the proximity of the altered amino acid residues to the histidines involved in heme ligation is considered, the results support a model for cytochrome b folding in which there are eight transmembrane domains rather than the nine of the Widger-Saraste model. Replacement of the Gly38 residue by valine results in resistance to the Qi inhibitors antimycin A and funiculosin but not 2-n-heptyl-hydroxyquinoline-N-oxide. Based upon sequence comparisons of mitochondrial and bacterial cytochrome b and chloroplast b6 proteins, the region of the molecule involved in antimycin binding is as highly conserved as those domains involved in heme ligation. It is suggested that the antimycin binding domain of cytochrome b is involved in forming the Qi reaction center. Alterations of the Gly142 and Thr147 residues result in resistance to myxothiazol and stimatellin, respectively. While both inhibitors block the Qo reaction center, the two mutations do not confer cross-resistance to each other. This region of cytochrome b is the most highly conserved during evolution and these inhibitor binding sites probably occur within the protein domain constituting the Qo reaction center. In addition, there is a less conserved region of the protein, defined by the Leu294 residue, which may function in binding the hydrophobic portions of Qo inhibitors.
J Mol Biol 1988 Oct 05
PMID:Mutational analysis of the mouse mitochondrial cytochrome b gene. 321 Feb 28

A region of the Saccharomyces cerevisiae mitochondrial cytochrome b gene encompassing the entire terminal intron plus flanking exonic sequences has been cloned in an SP6 vector. A runoff transcript prepared from this construct as well as the native cytochrome b pre-mRNA containing the terminal intervening sequence were found to act as substrates for the autocatalytic excision of the intervening sequence in vitro. This reaction proceeds under conditions previously shown by Cech and co-workers to promote protein-independent excision of the Tetrahymena rRNA intervening sequence. The 5' and 3' termini of the excised intervening sequence, determined by S1 nuclease mapping and sequence analysis, are consistent with the known sequence of the cytochrome b mRNA. The same region of the cytochrome b gene from a yeast mutant, defective in splicing due to a mutation in a critical sequence inside the terminal intron, has also been cloned in an SP6 vector. The mutant transcript fails to self-splice in the in vitro assay. These observations provide strong presumptive evidence that in vivo processing of the terminal intervening sequence of the cytochrome b pre-mRNA occurs by an autocatalytic mechanism analogous to that shown for other group I introns. In vivo processing of the terminal intervening sequence of the cytochrome b pre-mRNA, however, exhibits complete dependence on a protein factor previously shown to be encoded by the nuclear gene CBP2.
Mol Cell Biol 1987 Jul
PMID:In vitro splicing of the terminal intervening sequence of Saccharomyces cerevisiae cytochrome b pre-mRNA. 330 80

Axenic culture amastigote-like forms of Trypanosoma cruzi, grown at 28 degrees C, reach a stationary phase after two generations, and differentiate to epimastigotes, which then resume growth. Axenic culture amastigotes readily ferment glucose to succinate and acetate, and do not excrete NH3; they have high activities of hexokinase and phosphoenolpyruvate carboxykinase, and very low citrate synthase activity; cytochrome o is absent, and cytochrome b-like is present at a very low level. Epimastigotes catabolize glucose and produce succinate and acetate at a considerably lower rate; they exhibit lower levels of hexokinase and carboxykinase, and much higher levels of citrate synthase and cytochromes o and b-like. They catabolize amino acids, as shown by excretion of NH3 to the medium. The results suggest that axenic culture amastigotes have an essentially glycolytic metabolism, and they acquire the ability to oxidize substrates such as amino acids only after differentiation to epimastigotes.
Mol Biochem Parasitol 1987 Nov
PMID:Aerobic glucose fermentation by Trypanosoma cruzi axenic culture amastigote-like forms during growth and differentiation to epimastigotes. 332 2

Functional organization of mitochondrial genome (maxicircle kinetoplast DNA (kDNA)) from a flagellate protozoan Crithidia oncopelti was studied by Northern hybridization. A set of overlapping transcripts were mapped in the conserved region of the maxicircle. Several large (3-4 kb) RNAs, overlapping two or more smaller transcripts were found. Four regions produce a couple of RNAs differing in size 50-100 bases. Southern hybridization with several probes from the maxicircle kDNA of Leishmania tarentolae allowed identification of some of the found transcripts as corresponding to NADH dehydrogenase, subunit IV (Nd IV), cytochrome oxidase, subunits I-II (Cox I-II), cytochrome b (Cyt. b), ORF6-genes. Regions, homologous to the probes used are arranged in the same fashion in C. oncopelti kDNA as related genes in L. tarentolae. The divergent region was proved to be poorly transcribed and to produce a set of RNAs from 0.5 to 2.3 kb. Some transcripts of the divergent region seem to hybridize with distant maxicircular fragments. Cross-hybridization of such fragments has shown the absence of the regions of continuous homology.
Mol Biochem Parasitol 1987 Dec
PMID:Transcripts of the maxicircle kinetoplast DNA of Crithidia oncopelti. 343 71

The widespread assumption that cytoplasts generated from human polymorphonuclear leukocytes (PMNs) are vesicles consisting solely of cytoplasm surrounded by plasma membrane and devoid of granule activity remains to be tested. PMN cytoplasts were prepared by centrifugation of intact cells on a Ficoll step gradient in the presence of cytochalasin B. Two granule membrane markers, Mol, a fluorometrically detectable antigen, and cytochrome b, both of which have been shown to translocate to the plasma membrane during granule release, were compared for their activity in cytoplasts and intact PMNs. We found that the amount of Mol detected on the plasma membrane of intact PMNs, as compared with other membrane markers (such as antigens LFA-1 and beta 2m), increased 1.6-fold upon exposure of PMNs to Ficoll plus cytochalasin B prior to centrifugation. Another twofold increase in Mol expression occurred upon cytoplast preparation. Release of the granule enzymes, vitamin B12-binding protein, and lysozyme were also followed and correlated well (r = .78 and .92) with the amount of Mol antigen present on the cell surface. Cytochrome b was also found to be higher (1.4-fold) on plasma membranes isolated from cytoplasts than on plasma membranes isolated from intact control cells. These results indicate that some fusion of granule membranes and plasma membranes occurred during treatment of PMNs with Ficoll plus cytochalasin b and during cytoplast preparation.
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PMID:Expression of specific granule markers on the cell surface of neutrophil cytoplasts. 351 66

A succinate-coenzyme Q reductase (complex II) was isolated in highly purified form from Ascaris muscle mitochondria by detergent solubilization, ammonium sulfate fractionation and gel filtration on a Sephadex G-200 column. The enzyme preparation catalyzes electron transfer from succinate to coenzyme Q1 with a specific activity of 1.2 mumol coenzyme Q1 reduced per min per mg protein at 25 degrees C. The isolated complex II is essentially free of NADH-ferricyanide reductase, reduced CoQ2-cytochrome c reductase and cytochrome c oxidase and consists of four major polypeptides with apparent molecular weights of 66 000, 27 000, 12 000 and 11 000 and two minor ones with Mr of 36 000 and 16 000. The complex II contained cytochrome b-558, a major constituent cytochrome of Ascaris mitochondria, at a concentration of 3.6 nmol per mg protein, but neither other cytochromes nor quinone. The cytochrome b-558 in the complex II was reduced with succinate. In the presence of Ascaris NADH-cytochrome c reductase (complex I-III) (Takamiya, S., Furushima, R. and Oya, H. (1984) Mol. Biochem. Parasitol. 13, 121-134), the cytochrome b-558 in complex II was also reduced with NADH and reoxidized with fumarate. These results suggest the cytochrome b-558 to function as an electron carrier between NADH dehydrogenase and succinate dehydrogenase in the Ascaris NADH-fumarate reductase system.
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PMID:Electron-transfer complexes of Ascaris suum muscle mitochondria. II. Succinate-coenzyme Q reductase (complex II) associated with substrate-reducible cytochrome b-558. 375 51

The effects of 10 days of thyroxine injection (15 micrograms/100 g body weight) on rat liver mitochondrial cytochrome concentration and on the percent reduction of the individual cytochromes during succinate-driven state III and IV respiration was spectrophotometrically determined at cytochrome-specific wave-length pairs. The concentrations of cytochromes b, c, total c (c + c1) and a a3 increased in hyperthyroid rats. The concentration of cytochrome c1 remained constant in euthyroid and hyperthyroid rats. Changes in the concentration of the membrane-bound cytochromes were also determined by difference spectra in cytochrome c-depleted mitochondrial membranes. Cytochromes b and a a3 showed increased concentrations in hyperthyroid rats while the concentration of cytochrome c1 remained unchanged. Hyperthyroid mitochondria showed increased reduction of cytochromes b, c1, c and total c during state III respiration and cytochromes c1, c, and total c during state IV respiration. The percent reduction of cytochrome b decreased during state IV respiration in the hyperthyroid mitochondria. These results suggest that the increase in respiration observed in the hyperthyroid state may be related to changes both in the mitochondrial cytochrome concentration and in the cytochrome reduction level.
Mol Cell Endocrinol 1985 Jul
PMID:Thyroxine-induced changes in rat liver mitochondrial cytochromes. 401 95

The DNA sequence of the cob region of the Schizosaccharomyces pombe mitochondrial DNA has been determined. The cytochrome b structural gene is interrupted by an intron of 2526 base-pairs, which has an open reading frame of 2421 base-pairs in phase with the upstream exon. The position of the intron differs from those found in the cob genes of Saccharomyces cerevisiae, Aspergillus nidulans or Neurospora crassa. The Sch. pombe cob intron has the potential of assuming an RNA secondary structure almost identical to that proposed for the first two cox1 introns (group II) in S. cerevisiae and the p1-cox1 intron in Podospora anserina. It has most of the consensus nucleotides in the central core structure described for this group of introns and its comparison with other group II introns allows the identification of an additional conserved nucleotide stretch. A comparison of the predicted protein sequences of group II intronic coding regions reveals three highly conserved blocks showing pairwise amino acid identities of 34 to 53%. These regions comprise over 50% of the coding length of the intron but do not include the 5' region, which has strong secondary structural features. In addition to the potential intron folding, long helical structures involving repetitive sequences can be formed in the flanking cob exon regions. A comparison of the Sch. pombe cytochrome b sequence with those available from other organisms indicates that Sch. pombe is evolutionarily distant from both budding yeasts and filamentous fungi. As was seen for the Sch. pombe cox1 gene (Lang, 1984), the cob exons are translated using the universal genetic code and this distinguishes Sch. pombe mitochondria from all other fungal and animal mitochondrial systems.
J Mol Biol 1985 Aug 05
PMID:The mitochondrial genome of the fission yeast Schizosaccharomyces pombe. The cytochrome b gene has an intron closely related to the first two introns in the Saccharomyces cerevisiae cox1 gene. 404 21

22 revertants of Saccharomyces cerevisiae with intragenic suppressors (supa) of cob exon mutations (G. Burger, Mol. Gen. Genet., in the press) were analyzed. They display either a reduced amount of cytochrome b, or a shifted maximum absorption wavelength of total cytochrome b or a reduced growth rate on glycerol. The relationship of physico-chemical properties (content, light absorption and midpoint potential of cytochromes bK and bT) and functional properties (electron transport and energy yield) has been examined. In seven of eight revertants with a shifted maximum absorption wavelength of cytochrome b neither growth rate nor electron transfer activity was affected. In 13 of 14 revertants, reduced content of cytochrome b corresponds to a reduced electron transport rate through the cytochrome bc1 segment. A lower enzymatic activity, which is not due to a quantitative but to a qualitative alteration of cytochrome b was found in two revertants. Two revertants show electron transport rates of wild-type level concomitant with a reduced growth rate on glycerol, obviously due to a less efficient energy coupling. All revertants were shown to contain a high and a low potential cytochrome b, referred to as bK and bT. Those cob-/supa mutations which shift the maximum absorption wavelength or diminish the content of cytochrome b affect both b cytochromes in all cases. The results support that electron transport and energy conservation are catalyzed by the unity of cytochrome bK and bT and that both heme centers are bound to an identical apoenzyme. Comparing electron flow rates of succinate:cytochrome c oxidoreductase and NADH:cytochrome c oxidoreductase in cob- mutants and two revertants provides evidence that ubiquinone does not constitute a homogeneous pool, suggested by the dissimilar interaction of both dehydrogenases with the bc1 segment.
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PMID:Cytochrome b of cob revertants in yeast. Bioenergetic characterization of revertants with reduced content and shifted maximum absorption wavelength of cytochrome b. 608 48


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