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Query: UNIPROT:O95477 (membrane-bound)
 29,236 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The membrane-bound NADPH:O2 oxidoreductase of human neutrophils has been solubilized in approximately 70% yield and purified on concanavalin A-Sepharose and gel sieving columns of varying bed volumes and sieving ranges. The half-life of the solubilized oxidoreductase stored at 2-4 degrees C in the presence of 25% glycerol at pH 8.6 is approximately 30 h. The oxidoreductase contains a flavoprotein identifiable by its fluorescence spectrum for FAD which binds weakly to concanavalin A-Sepharose and elutes from gel sieving columns at a molecular weight range of approximately 51,000. This flavoprotein accounts for approximately 70% of the total FAD content found in granular membrane fractions recovered from activated neutrophils. Recovery of oxidoreductase activity from both concanavalin A-Sepharose affinity and gel sieving columns is affected by the resolution of the flavoprotein free of the cytochrome b component of the oxidoreductase. The resolved flavoprotein and cytochrome b appear unable to catalyze either NADH nor NADPH oxidase activities with O2, ferricyanide, or nitroblue tetrazolium salt serving as electron acceptors.
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PMID:Purification of the solubilized NADPH:O2 oxidoreductase of human neutrophils. Isolation of its catalytically inactive cytochrome b and flavoprotein redox centers. 335 2

Cytochrome b comprising 91-kDa and 22-kDa subunits is a critical component of the membrane-bound oxidase of phagocytes that generates superoxide. This important microbicidal system is impaired in inherited disorders known as chronic granulomatous disease (CGD). Previously we determined the sequence of the larger subunit from the cDNA of the CGD gene, the X chromosome locus affected in "X-linked" CGD. To complete the primary structure of the cytochrome b and to assess expression of the smaller subunit, we isolated cDNA clones for the 22-kDa polypeptide by immunoscreening and confirmed their authenticity by direct N-terminal protein sequencing. Although the deduced amino acid sequence of the 22-kDa subunit is not overtly similar to other known cytochromes, we observed a 31-amino acid stretch of 39% identity with polypeptide I of mitochondrial cytochrome c oxidase centered on a potential heme-coordinating histidine. Similarities in the hydropathy profiles and spacing of histidines of the 22-kDa protein and myoglobin suggest structural motifs in common with other heme-containing proteins that are not readily revealed by primary amino acid sequences. Although RNA for the larger subunit has been found only in cells of the phagocytic lineage, stable RNA encoding the 22-kDa subunit was observed in all cell types. However, the stable 22-kDa protein was detected only in phagocytic cells that were expressing the larger subunit RNA. This observation suggests that the large subunit may play a role in regulating the assembly of the heterodimeric cytochrome b.
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PMID:Primary structure and unique expression of the 22-kilodalton light chain of human neutrophil cytochrome b. 336 42

A new membrane-bound b-type cytochrome, cytochrome b-558, was removed from chromatophore membranes of photosynthetically grown Rhodopseudomonas sphaeroides strain R-26 by deoxycholate-cholate extraction. The cytochrome was purified by ammonium sulfate fractionation and ion-exchange chromatography. Cytochrome b-558 had absorption maxima at 280 and 405 nm in the oxidized form, and at 558, 528, and 420 nm in the reduced form. It had a midpoint potential of--130 mV at pH 7.0. The minimal molecular weight of this protein was 42,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and it contained one mole heme per mole of protein. The isoelectric point was 8.5. The electrophoretic pattern of heme-carrying proteins and the redox potentiometry showed that cytochrome b-558 was present in membranes from wild type, strain R-26, and strain GA grown photosynthetically, but not from any strain grown aerobically.
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PMID:A new membrane-bound b-type cytochrome, cytochrome b-558, from photosynthetically grown Rhodopseudomonas sphaeroides. 348 57

Mutant strains of Rhizobium japonicum constitutive for H2 uptake activity (Hupc) contained significantly more membrane-bound b-type cytochrome than did the wild type when grown heterotrophically. The Hupc strains contained approximately three times more dithionite- and NADH-reducible CO-reactive b-type cytochrome than did the wild type; the absorption features of the CO spectra were characteristic of cytochrome o. This component, designated cytochrome b', was not reduced by NADH in the presence of cyanide. Cytochrome o from the wild type (SR) and cytochrome b' from mutants SR476 and SR481 bound to CO with similar dissociation constants of 5.4, 7.4, and 5.6 microM, respectively. NADH-dependent reduction of cytochrome b' from SR476 and SR481 and the cytochrome o from SR followed pseudo-first-order kinetics with similar rate constants. Based on these spectral, ligand-binding, and kinetic measurements, it was concluded that cytochrome b' expressed by the Hupc mutants is equivalent to cytochrome o found in the wild type. H2, NADH, and succinate each reduced the same amount of total b-type cytochrome in membranes from SR481, and the rate of H2-dependent cytochrome o reduction was significantly less than with succinate or NADH as the reductants. It was concluded that neither cytochrome o nor any b-type cytochrome expressed by the Hupc mutants was unique to the H2 oxidation system. At low O2 concentrations, the inhibition of H2 and NADH oxidase activities by CO closely paralleled the binding of CO to cytochrome o rather than cytochromes a3 or c'. This suggested that NADH and H2 oxidation involved primarily cytochrome o as the terminal oxidase at low O2 tensions.
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PMID:Expression of cytochrome o in hydrogen uptake constitutive mutants of Rhizobium japonicum. 396 33

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.
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PMID:Thyroxine-induced changes in rat liver mitochondrial cytochromes. 401 95

Rat liver microsomal fractions have been equilibrated in various types of linear density gradients. 15 fractions were collected and assayed for 27 constituents. As a result of this analysis microsomal constituents have been classified, in the order of increasing median density, into four groups labeled a, b, c, and d. Group a includes: monoamine oxidase, galactosyltransferase, 5'-nucleotidase, alkaline phosphodiesterase I, alkaline phosphatase, and cholesterol; group b: NADH cytochrome c reductase, NADPH cytochrome c reductase, aminopyrine demethylase, cytochrome b(5), and cytochrome P 450; group c: glucose 6-phosphatase, nucleoside diphosphatase, esterase, beta-glucuronidase, and glucuronyltransferase; group d: RNA, membrane-bound ribosomes, and some enzymes probably adsorbed on ribosomes: fumarase, aldolase, and glutamine synthetase. Analysis of the microsomal fraction by differential centrifugation in density gradient has further dissociated group a into constituents which sediment more slowly (monoamine oxidase and galactosyltransferase) than those of groups b and c, and 5'-nucleotidase, alkaline phosphodiesterase I, alkaline phosphatase, and the bulk of cholesterol which sediment more rapidly (group a2). The microsomal monoamine oxidase is attributed, at least partially, to detached fragments of external mitochondrial membrane. Galactosyltransferase belongs to the Golgi complex. Group a2 constituents are related to plasma membranes. Constituents of groups b and c and RNA belong to microsomal vesicles derived from the endoplasmic reticulum. These latter exhibit a noticeable biochemical heterogeneity and represent at the most 80% of microsomal protein, the rest being accounted for by particles bearing the constituents of groups a and some contaminating mitochondria, lysosomes, and peroxisomes. Attention is called to the operational meaning of microsomal subfractions and to their cytological complexity.
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PMID:Analytical study of microsomes and isolated subcellular membranes from rat liver. 3. Subfractionation of the microsomal fraction by isopycnic and differential centrifugation in density gradients. 415 Apr 90

Hexachlorophene (HCP) inhibits both endogenous and exogenous respiration (oxygen uptake) in Bacillus megaterium, without sparing by any of several substrates. The inhibition is maximal when the cells are treated with 8 mug of HCP per mg of cells (dry weight), which corresponds to the minimal lethal dose. Levels as low as 2 mug/mg are inhibitory but not lethal. HCP also inhibits the respiration of isolated B. megaterium membranes and can act on several components of the electron transport chain in the membranes and on soluble enzymes. Although both forms of nicotinamide adenine dinucleotide, reduced form dehydrogenase and malic dehydrogenase are inhibited by HCP, they are less susceptible than is oxygen uptake. The site of maximal sensitivity is nearer the terminal electron acceptor, but the exact location depends on the cytochrome composition of the membranes. If cytochromes b(1), a, and a(3) are present, but not o, HCP inhibits electron transport on the substrate side of cytochrome b(1); if cytochromes b(1), a(3), and o are present, but not a, the inhibition occurs on the oxygen side of cytochrome b(1). Exogenous menadione, an analogue of menaquinone, reverses the inhibition in both circumstances. The primary lethal action of HCP thus appears to be respiratory inhibition at a site within the membrane-bound part of the electron transport chain.
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PMID:Antimicrobial actions of hexachlorophene: inhibition of respiration in Bacillus megaterium. 421 82

The catabolism of glucose by Haemophilus parainfluenzae affected the formation of the primary dehydrogenases of the membrane-bound electron transport system. The formation of other components of the respiratory system, 2-demethyl vitamin K(2), cytochrome b(1), cytochrome c(1), and the cytochrome oxidases a(1), a(2), and o, is not affected by the catabolism of glucose. The formation of all components of the electron transport system is controlled by the identity and concentration of the terminal electron acceptors present in the growth medium.
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PMID:Effect of glucose on the formation of the membrane-bound electron transport system in Haemophilus parainfluenzae. 428 51

Addition of oxygen to a culture of anaerobically growing Staphylococcus aureus results in the formation of a membrane-bound, functional electron transport system. With the shift to aerobic growth, there is at least a 15-fold increase in cytochrome a and at least a 55-fold increase in cytochrome oxidase o. At the completion of the shift to aerobic growth, the cytochrome levels equal those found in bacteria grown with aeration throughout the entire growth cycle. Cytochromes b(1) and o are formed first. Their synthesis slows when cytochrome a becomes detectable. Concentrations of cytochromes b(1) and sometimes cytochrome a increase late in the adaptive period. Concomitant with this is a decrease in the oxygen tension at which the rate of oxygen utilization becomes dependent on the oxygen concentration. During the shift to aerobic growth, the protoheme content increases ninefold, and all the protoheme can be accounted for in enzymatically reducible cytochrome b(1) and cytochrome oxidase o. Protoheme, but not a functional cytochrome system, is synthesized by anaerobically growing S. aureus. Heme a appears only after a period of aerobic growth. During the shift to aerobic growth, there is a 1.6-fold increase in the vitamin K(2) content, with an alteration in the ratios of the 35 and 45 carbon side chain isoprenologues. A twofold increase in phosphatidyl glycerol and a 1.6-fold increase in cardiolipin occur with the shift to aerobic growth. Lysyl-phosphtidyl glycerol remains essentially constant in this period. Concentrations of mono- and diglucosyl diglycerides increase coordinately 1.3-fold during the shift to aerobic growth at a 2.5 to 1 m ratio.
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PMID:Membrane lipid changes during formation of a functional electron transport system in Staphylococcus aureus. 429 93

Nuclear membranes were isolated from rat and pig liver by sonication of highly purified nuclear fractions and subsequent removal of adhering nucleoproteins in a high salt medium. The fractions were examined in the electron microscope by both negative staining and thin sectioning techniques and were found to consist of nuclear envelope fragments of widely varying sizes. Nuclear pore complex constituents still could frequently be recognized. The chemical composition of the nuclear membrane fractions was determined and compared with those of microsomal fractions prepared in parallel. For total nuclei as well as for nuclear membranes and microsomes, various enzyme activities were studied. The results indicate that a similarity exists between both fractions of cytomembranes, nuclear envelope, and endoplasmic reticulum, with respect to their RNA:protein ratio and their content of polar and nonpolar lipids. Both membranous fractions had many proteins in common including some membrane-bound enzymes. Activities in Mg-ATPase and the two examined cytochrome reductases were of the same order of magnitude. The content of cytochrome b(5) as well as of P-450 was markedly lower in the nuclear membranes. The nuclear membranes were found to have a higher buoyant density and to be richer in protein. The glucose-6-phosphatase and Na-K-ATPase activities in the nuclear membrane fraction were very low. In the gel electrophoresis, in addition to many common protein bands, some characteristic ones for either microsomal or nuclear membranous material were detected. Significant small amounts of DNA and RNA were found to remain closely associated with the nuclear envelope fragments. Our findings indicate that nuclear and endoplasmic reticulum membranes which are known to be in morphological continuity have, besides a far-reaching similarity, some characteristic differences.
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PMID:Nuclear membranes from mammalian liver. I. Isolation procedure and general characterization. 431 31


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