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Query: UNIPROT:P06889 (Mol)
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The kinetics of polar body formation were examined in parthenogenetically activated, in vitro matured and aged bovine oocytes. Subsequently, the presence or absence of polar body formation was determined in bovine embryo clones. Polar body formation, defined as telophase II, occurred by 1 (13/40, 43%) and 2 h (15/21, 71%) postparthenogenetic activation of metaphase II stage oocytes. Parthenogenetically activated oocytes readily formed pronuclei by 4 h. Some oocytes had chromatin in a highly condensed state at 1, 2, and 4 h postactivation (13/72, 18%). These oocytes often (10/13, 77%) appeared to be "self-enucleated," as the condensed chromatin was found in a membrane-bound extrusion. The phenomenon was most prevalent when oocytes were handled at room temperature (25-27 degrees C). Nuclear transfer procedures were established to bring about synchronous blastomere fusion and oocyte activation conditions. Synchronous conditions were achieved only when oocytes were handled and manipulated at 37-39 degrees C. Embryo clones examined 2 h postfusion did not form a polar body. Conversely, nucleate demi-oocyte controls were at the late telophase II stage of meiosis. The results are discussed in relation to cell cycle effects on bovine nuclear transfer.
Mol Reprod Dev 1992 Sep
PMID:The kinetics of oocyte activation and polar body formation in bovine embryo clones. 151 Aug 44

NADH:ubiquinone oxidoreductase, the first enzyme in the respiratory electron transport chain of mitochondria, is a membrane-bound multi-subunit assembly, and the bovine heart enzyme is now known to contain about 40 different polypeptides. Seven of them are encoded in the mitochondrial DNA; the remainder are the products of nuclear genes and are imported into the organelle. The primary structures of 12 of the nuclear coded subunits have been described and those of a further 20 are described here. The subunits have been sequenced by following a strategy based on the polymerase chain reaction. This strategy has been tailored from existing methods with the twofold aim of avoiding the use of cDNA libraries, and of obtaining a cDNA sequence rapidly with minimal knowledge of protein sequence, such as can be determined in a single N-terminal sequence experiment on a polypeptide spot on a two-dimensional gel. The utility and speed of this strategy have been demonstrated by sequencing cDNAs encoding 32 nuclear-coded-membrane associated proteins found in bovine heart mitochondria, and the procedures employed are illustrated with reference to the cDNA sequence of the 20 subunits of NADH:ubiquinone oxidoreductase that are presented. Extensive use has also been made of electrospray mass spectrometry to measure molecular masses of the purified subunits. This has corroborated the protein sequences of subunits with unmodified N terminals, and their measured molecular masses agree closely with those calculated from the protein sequences. Nine of the subunits, B8, B9, B12, B13, B14, B15, B17, B18 and B22 have modified alpha-amino groups. The measured molecular masses of subunits B8, B13, B14 and B17 are consistent with the post-translational removal of the initiator methionine and N-acetylation of the adjacent amino acid. The initiator methionine of subunit B18 has been removed and the N-terminal glycine modified by myristoylation. Subunits B9 and B12 appear to have N-terminal and other modifications of a hitherto unknown nature. The sequences of the subunits of bovine complex I provide important clues about the location of iron-sulphur clusters and substrate and cofactor binding sites, and give valuable information about the topology of the complex. No function has been ascribed to many of the subunits, but some of the sequences indicate the presence of hitherto unsuspected biochemical functions. Most notably the identification of an acyl carrier protein in both the bovine and Neurospora crassa complexes provides evidence that part of the complex may play a role in fatty acid biosynthesis in the organelle, possibly in the formation of cardiolipin.(ABSTRACT TRUNCATED AT 400 WORDS)
J Mol Biol 1992 Aug 20
PMID:Sequences of 20 subunits of NADH:ubiquinone oxidoreductase from bovine heart mitochondria. Application of a novel strategy for sequencing proteins using the polymerase chain reaction. 151 44

A membrane-bound sialidase (EC 3.2.1.18) was found in procyclic trypomastigotes of Trypanosoma brucei. The mammalian stage bloodstream form, however, displayed no sialidase activity. This sialidase is an integral surface protein, linked to the membrane via a glycosylphosphatidylinositol anchor. After osmotic lysis and solubilization with Triton CF-54, the enzyme was purified 1900-fold by gel filtration and ion exchange chromatography. Its size, as determined by conventional and high-performance liquid gel chromatography, is 67 kDa. The sialidase is active over a broad pH and temperature range with optima at pH 6.9 and 35 degrees C, respectively. No loss of activity is observed after 4 freeze-thaw cycles. T. brucei sialidase activity is inhibited by N-(4-nitrophenyl)oxamic acid and 2-deoxy-2,3-didehydro-N-acetylneuraminic acid, the latter, however, being less effective. N-Acetylneuraminic acid shows no inhibitory effect, whereas a variety of metal ions are potent inhibitors. The sialidase is activated by di- and tricarboxylic acids, but inhibited by chloride. Relative hydrolysis rates of various sialic acid-containing compounds reveal that de-O-acetylated bovine submandibular gland mucin is the preferred substrate and that alpha(2-3)-linkages are hydrolyzed faster than alpha(2-6)-linkages.
Mol Biochem Parasitol 1992 Aug
PMID:Purification and characterization of a novel sialidase found in procyclic culture forms of Trypanosoma brucei. 151 30

The amyloid precursor protein (APP) is a glycoprotein consisting of at least four isoforms derived from a single gene by a process of alternative splicing. The membrane-bound forms of APP have been suggested to have adhesive properties and to mediate neural cell adhesion. Previous studies have demonstrated the ability of Fab' fragments of antibodies to extracellular domains of APP to inhibit neural cell binding to a collagen substrate, suggesting a physiological role for the collagen-binding properties of APP. The binding of APP has been demonstrated to be specific for type IV collagen, and no binding to other extracellular matrix components, including fibronectin and laminin, was detected. The APP-collagen binding appeared to be mediated by a heparin-bridge mechanism, since the binding was abolished by the addition of excess heparan or heparinase. These results were observed by both a homogenate-collagen binding assay and a cell-surface adhesion assay, thus providing further evidence for the adhesion role of APP. They also pose the question of the possible role of the heparin-binding properties of APP in the genesis of the neuritic plaques characteristic of Alzheimer's disease.
Mol Chem Neuropathol
PMID:APP-collagen interaction is mediated by a heparin bridge mechanism. 152 Apr

Incubation of rat brain synaptosomes and mitochondria with LPO inducers (Fe2+ and ascorbate) was accompanied by a decrease of deamination of serotonin (substrate of MAO-A) in mitochondria, but not in synaptosomes, with simultaneous stimulation of GABA and GLCA deamination, apparently owing to modification of catalytic properties of brain membrane-bound MAO. Oxidation of PEA (substrate of MAO-B) was insignificantly altered in both fractions. Reactions of deamination of serotonin, GABA, and GLCA (but not PEA), were highly sensitive to a selective inhibitor of MAO-A pyrazidol (pyrlindole). Isoniazid and hydrazides of quinoline carbonic acids (inhibitors of both modified MAO and copper-containing amine oxidases) strongly inhibited deamination of GABA and GLCA. During epileptiformic seizures in rats, genetically selected for high incidence of audiogenic epilepsia, stimulation in brain synaptosomes and mitochondria of LPO was observed. This was accompanied by a marked decrease in serotonin and PEA deamination, with a simultaneous increase in GABA and GLCA deamination in both fractions. The data obtained suggest that appearance of GABA-deaminating activity owing to modification of catalytic properties of MAO, might be an essential pathogenetic component in the development of epileptic seizures.
Mol Chem Neuropathol
PMID:The role of lipid peroxidation in the possible involvement of membrane-bound monoamine oxidases in gamma-aminobutyric acid and glucosamine deamination in rat brain. Focus on chemical pathogenesis of experimental audiogenic epilepsy. 152 Apr 3

Two nitrate reductases, NRA and NRZ, are present in Escherichia coli. These isoenzymes have the same alpha beta gamma, subunits composition and have similar size and genetic organization. Corresponding subunits of the complexes share at least 75% identity. By subcloning the different genes and expressing them from separate transcriptional units, we have demonstrated (i) that the translation of the subunits and their assembly are not coupled processes, since subunits produced concomitantly but independently can meet efficiently and associate to form active enzymes, and (ii) that the alpha subunit of a given complex can be replaced by its counterpart from the other isoenzyme to yield an active membrane-bound heterologous enzyme. One such heterologous enzyme, alpha A beta Z gamma Z, has been purified; it is less stable than the native enzymes, more susceptible to thermal denaturation, and shows increased sensitivity to proteolysis. It is also less stably bound to the membrane and, consequently, its activity with physiological electron donors is drastically reduced. The possibility that heterologous nitrate reductases could be formed in vivo is discussed with reference to the existence of porin heterotrimers of the outer membrane proteins OmpC, OmpF and PhoE.
Mol Microbiol 1992 Jan
PMID:Formation of active heterologous nitrate reductases between nitrate reductases A and Z of Escherichia coli. 154 5

Two membrane-bound nitrate reductases, NRA and NRZ, exist in Escherichia coli. Both isoenzymes are composed of three structural subunits, alpha, beta, and gamma encoded by narG/narZ, narH/narY and narI/narV, respectively. The genes are in transcription units which also contain a fourth gene encoding a polypeptide, delta, which is not part of the final enzyme. A strain which is devoid of, or does not express, the nar genes, was used to investigate the role of the delta and gamma polypeptides in the formation and/or processing of the nitrate reductase. When only the alpha and beta polypeptides are produced, an (alpha beta) complex exists which is inactive and soluble. When the alpha, beta and delta polypeptides are produced, the (alpha beta) complex is active with artificial donors such as benzyl viologen but is soluble. When the alpha, beta and gamma polypeptides are produced, the (alpha beta) complex is inactive but partially binds the membrane. It was concluded that the gamma polypeptide is involved in the binding of the (alpha beta) complex to the membrane while the delta polypeptide is indispensable for the (alpha beta) nitrate reductase activity. The activation by the delta polypeptide does not seem to involve the insertion of the redox centres of the enzyme since the purified inactive (alpha beta) complex was shown to contain the four iron-sulphur centres and the molybdenum cofactor, which are normally present in the native purified enzyme. The extreme sensitivity of this inactive complex to thermal denaturation or tryptic treatment favours the idea that the delta polypeptide promotes the correct assembly of the alpha and beta subunits. Although this corresponds to the definition of a chaperone protein this possibility has been rejected. In this study we have also demonstrated that the delta or gamma polypeptide encoded by one nar operon can be substituted successfully for by its respective counterpart from the other nar operon to give an active membrane bound heterologous nitrate reductase enzyme.
Mol Microbiol 1992 Jan
PMID:Involvement of the narJ or narW gene product in the formation of active nitrate reductase in Escherichia coli. 154 6

Sbarra and Karnovsky were the first to present evidence suggesting the presence in phagocytes of a special enzyme designed to generate reactive oxidants for purposes of host defense. In the years since their report appeared, a great deal has been learned about this enzyme, now known as the respiratory burst oxidase. It has been found to be a plasma membrane-bound heme- and flavin-containing enzyme, dormant in resting cells, that catalyzes the one-electron reduction of oxygen to O2- at the expense of NADPH: O2 + NADPH----O2- + NADP+ + H+ Its behavior in whole cells and its response to various activating stimuli have been described in detail, although important insights continue to emerge, as for example a very interesting new series of observations on differences in oxidase activation patterns between suspended and adherent cells. The enzyme has been shown by biochemical and genetic studies to consist of at least six components. In the resting cell, three of these components are in the cytosol and three in the plasma membrane, but when the cell passes from its resting to its activated state the cytosolic components are all transferred to the plasma membrane, presumably assembling the oxidase. Of the components initially bound to the membrane, two constitute cytochrome b558, a heme protein characteristic of the respiratory burst oxidase, and the third may represent an oxidase flavoprotein. With regard to the cytosolic components, one is a phosphoprotein and another is the NADPH-binding component, possibly a second oxidase flavoprotein. The nature of the third (p67phox) is a puzzle. Four of the six oxidase components have now been cloned and sequenced. These findings only scratch the surface, however, and many questions remain. How many oxidase components, for example, remain to be discovered, and how do they fit together to form the active enzyme? How is the route of activation of the oxidase integrated into the general signal transduction systems of the cell? How did the oxidase come to be? Could there be a widespread system that generates small amounts of O2- as an intercellular signaling molecule, as recent work is beginning to suggest, and did the ever-destructive respiratory burst oxidase arise from that innocuous system as the creation of some evolutionary Frankenstein--an oxidase from hell? Finally, will it be possible to develop drugs that specifically block the respiratory burst oxidase, and will such drugs prove to be clinically useful as anti-inflammatory agents?(ABSTRACT TRUNCATED AT 400 WORDS)
Adv Enzymol Relat Areas Mol Biol 1992
PMID:The respiratory burst oxidase. 157 Jul 69

The activity of phospholipid base exchange enzymes has been evaluated in cardiac sarcolemmal membranes from Syrian Golden hamsters and from a hamster strain (UM-X7.1) characterized by a genetic form of hypertrophic cardiomyopathy. No choline base exchange activity and only a little serine base exchange activity were detected, whereas the ethanolamine base exchange enzyme was found highly active in membranes from both strains. For this reason, the present study is focussed on the ethanolamine base exchange enzyme. The apparent Km for ethanolamine of ethanolamine base exchange enzyme from Syrian Golden membranes and from UM-X7.1 strain membranes are 18 and 32 microM, respectively. The specific activity of the sarcolemmal ethanolamine base exchange enzyme is lower in the UM-X7.1 strain than in Syrian Golden hamsters. The calcium-dependence of the enzyme appears different when the membranes from the two strains are compared. Indeed, after removal of the membrane-bound divalent cations, comparable activities are found in both membrane preparations, whereas, upon addition of Ca2+ to the incubation mixtures, the activity of the enzyme is enhanced in the membranes from Syrian Golden strain more than in those from UM-X7.1 strain. The cholesterol content of sarcolemmal membranes is higher in the cardiomyopathic strain than in the Syrian Golden hamsters. A possible relation between changes of the membrane lipid composition and of the ethanolamine base exchange activity is discussed.
Mol Cell Biochem 1992 Mar 04
PMID:Phospholipid base exchange enzyme activity in sarcolemmal membranes from the heart of cardiomyopathic hamsters. 157 31

Fc receptors (FcRs) are immunoglobulin-binding structures that enable antibodies to perform a variety of functions by forming connections between specific recognition and effector cells. Besides eliciting cytotoxicity, inducing secretion of mediators and endocytosis of opsonized particles, FcRs are involved in the regulation of antibody production, both as integral membrane proteins and as soluble molecules released from the cell surface. Most FcRs belong to the same family of proteins as their ligands (immunoglobulin superfamily). This review contains recent data obtained by use of monoclonal antibodies and cloning studies on FcRs and FcR-like molecules. The importance of fine specificity of receptor binding site(s)--that of the conformation of FcRs and their ligands in triggering signaling mechanisms--is analyzed. The regulatory function of membrane-bound and -released FcRs; the correlation between cell cycle, FcR expression, and release; as well as the possible mechanisms of these phenomena are discussed.
Crit Rev Biochem Mol Biol 1992
PMID:Regulation of antibody production mediated by Fc gamma receptors, IgG binding factors, and IgG Fc-binding autoantibodies. 158 43


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