UNIPROT:O95477 - FACTA Search

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

The amount of 125I-IgG which bound to membranes isolated from the human placenta was competitively inhibited by the presence of increasing amounts of unlabeled IgG but not by unlabeled albumin. The relationship between membrane-bound and free IgG indicated the presence of membrane receptors with an appreciable affinity for IgG. Incubation of membranes with collagenase or neuraminidase did not results in appreciable reduction of IgG-membrane binding, indicating that neither intact collagen nor sialic acid play an important role in the binding. Placental surface membranes isolated by salt extraction bound 3.79+/- 1.78 (SD) pmol IgG/microgram membrane protein, whereas membranes isolated by differential centrifugation bound only 1.61 +/- 0.24 pmol/microgram (p less than 0.02). The fraction of a preparation of solubilized membranes which bound to an IgG affinity column yielded on polyacrylamide gel electrophoresis three prominent protein bands which had molecular weights of 3.7 X 10(4), 4.5 X 10(4) and 6.0 X 10(4) daltons. These findings are consistent with the existence of a limited number of receptors for IgG on placental membranes, including IgG receptors on the microvillus membrane of the syncytial trophoblast. The latter, in accordance with Brambell's hypothesis, could be of importance in the transplacental transport of maternal IgG.
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PMID:Properties of receptors for IgG on human placental cell membranes. 63 15

1. Segments of mouse or rat pancreas were placed in a flow cell through which physiological salt solutions of varying composition were pumped at a constant rate. Intracellular recordings of membrane potential, resistance and electrical time constant were made from the acini using fine glass micro-electrodes. In some experiments two micro-electrodes were inserted into two acinar cells within the same acinus to assess directly cell to cell coupling. The concentration of amylase in the effluent was measured continuously. 2. Electrical coupling between two acinar cells was observed when the tips of the two micro-electrodes were less than 50 mum from each other. The coupling ratio was close to 1. Acetylcholine (ACh) always evoked depolarization of exactly the same amplitude in two coupled cells and reduced the amplitude of current-pulse induced membrane potential changes in both cell simultaneously. 3. Stimulation with ACh caused an immediate increase in amylase output. Replacement of superfusion fluid Na by Tris or Cl by sulphate abolished ACh-evoked increase in amylase release, but the subsequent reintroduction of Na or Cl caused an increase in amylase release of a magnitude similar to what was normally observed following stimulation. 4. Omitting Ca from the superfusion fluid and adding EGTA rapidly depolarized the acinar cell membrane, reduced the input resistance and caused a marked reduction in amylase secretion. During exposure to a Ca-free, EGTA containing solution a marked increase in amylase release occurred following maximal ACh stimulation. 5. Addition of small amounts of Mg, Ca or Mn to a Ca-, Mg-free solution caused an increase in membrane potential, input resistance and electrical time constant and markedly increased amylase release. The effect on the electrical parameters was reversed in the absence of extracellular Na while extracellular Na was of no importance for the effect on amylase release. 6. The effect of ACh on amylase was enhanced during superfusion with a fluid containing 20 mM-Ca. The presence of Mn (5 mM) in an otherwise normal control had no effect on ACh-evoked release. 7. These results show that ACh acts on the acinus by reducing the surface cell membrane resistance. It is suggested that the ACh-receptor interaction causes a release of Ca from the surface cell membrane and that the concentration of Ca in the surface cell membrane determines the specific membrane resistance particularly for Na. The release of Ca to the cytosol activates exocytosis while the Na influx is of importance for acinar fluid secretion. The effect of ACh on amylase secretion can be mimicked by agents displacing membrane-bound Ca (Mg, Ca, Mn).
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PMID:Pancreatic acinar cells: the role of calcium in stimulus-secretion coupling. 81 43

Previous work has shown that the 26S RNA found in Sindbis-infected chicken embryo fibroblasts encodes the three viral structural proteins, one internal protein, core, and two membrane glycoproteins, E1 and E2. This mRNA has one initiation site; core, E1, and E2 are derived by proteolytic cleavage. Here we show that during infection, the 26S RNA is found mainly in membrane-bound polysomes which synthesize all three virion structural proteins. These polysomes are released from the membrane upon treatment with puromycin and high salt. Newly synthesized core protein is localized on the cytoplasmic side of endoplasmic reticulum membranes, while newly synthesized envelope proteins are sequestered by the lipid bilayer. These results suggest that the nascent glycoproteins, presumably their amino termini, are of major importance in directing the binding of polysomes containing 26S mRNA to endoplasmic reticulum membranes and the subsequent transfer of glycoproteins into the bilayer.
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PMID:How a single Sindbis virus mRNA directs the synthesis of one soluble protein and two integral membrane glycoproteins. 83 48

Biochemical localization of the enzyme as a function of age of cell culture showed the alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) activity of Bacillus licheniformis MC14 predominantly in the particulate cell fraction in early- and mid-log cells. However, in late-log and stationary cells, increasing amounts of activity were found in the soluble fraction of lysed cells. Upon protoplast formation of these cells, the activity was released into the soluble fraction. No alkaline phosphatase activity was found in either the cytoplasmic fraction or in the cell medium during any phase of cell growth. The soluble fraction released on protoplast formation that contained alkaline phosphatase activity showed immunological cross-reactivity with antibody to the purified heat--salt-solubilized membrane alkaline phosphatase (F. M. Hulett-Cowling and L. L. Campbell, 1971). Theparticulate membrane fraction containing a firmly associated alkaline phosphatase also showed similar cross-reactivity. Further, the effectiveness of nonionic detergents, ionic detergents, bile salts, and various concentrations of magnesium and sodium as solubilizing agents for this membrane-bound alkaline phosphatase was investigated. Hexadecyl pyridinium chloride (0.03 M) and magnesium and sodium salts (above 0.2 M) were effective solubilizing agents. The substrate specificities of the various fractions were determined and compared to the substrate specificities of the purified membrane alkaline phosphatase.
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PMID:Biochemical localization of the alkaline phosphatase of Bacillus licheniformis as a function of culture age. 83 74

Rat liver mRNA-labeled free and membrane-bound polysomes uncontaminated with nuclear or cytoplasmic ribonucleoprotein particles were dissociated with EDTA and the released messenger ribonucleoprotein particles isolated using an oligo(dT)-cellulose column. Seventy percent of the labeled mRNA applied bound to the column. Binding of mRNP was dependent on the presence of a poly(A) segment in the RNA. The nonbound material contained most of the ribosomal subunits and also messenger-sized poly(A-)RNA molecules associated with protein. The free mRNP fraction bound to the column, washed with 250 mM NaCl, and subsequently eluted contained seven proteins ranging in molecular weight from 52 000 to 138 000 only one of which was found in the fraction not bound to the column. Furthermore, these proteins were shown to have a higher affinity for poly(A+)RNA as compared with rRNA. The membrane-bound mRNP contained five proteins, four of which were identical with those associated with free mRNP. Membrane-bound mRNP were disrupted at a lower salt concentration than the free. The proteins found associated with free and membrane-bound polysomal mRNP appeared to be clustered in the poly(A) region of the molecule. The implications of these findings are discussed.
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PMID:Isolation and characterization of rat liver free and membrane-bound polysomal messenger ribonucleoprotein particles. 91 16

Messenger RNA (mRNA) of membrane-bound polysomes in a membrane fraction of WI-38 cells remains associated with the microsomal membranes even after ribosomes and their nascent polypeptide chains are removed by using puromycin in a high salt buffer or by disassembling the ribosomes in a medium of high ionic strength lacking magnesium. mRNA either was specifically labeled in the presence of actinomycin D, or it was recognized by virtue of its affinity for oligo-dT. Poly A segments in bound mRNAs have an electrophoretic mobility in acrylamide gels which is characteristic of cytoplasmic mRNAs and corresponds to 150-200 adenyl residues. Extensive RNase treatment did not lead to release of the poly A segments of membrane-associated mRNA molecules either from an intact membrane fraction or from a membrane fraction previously stripped of ribosomes. On the other hand, RNase treatment led to the release and digestion of the nonpoly A segments of the mRNA molecules, indicating that the site of attachment of mRNA to the ER membranes is located near or at the 3' end of the molecule which contains the poly A. A direct association of mRNAs and endoplasmic reticulum membranes is considered in a modelto explain the assembly of bound polysomes and protein synthesis in a membrane-associated apparatus.
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PMID:Direct association of messenger RNA with microsomal membranes in human diploid fibroblasts. 113 14

UDP-D-Galactose:D-xylose galactosyltransferase, a membrane-bound enzyme which catalyzes the second glycosyl transfer reaction in the biosynthesis of chondroitin sulfate chains, has been solubilized and partially purified from embryonic chick cartilage. Solubilization was effected by treatment of a particulate fraction of a homogenate (sedimenting between 10,000 and 100,000 times g) with the nonionic detergent Nonidet P-40 (0.5%) and KCl (0.5 M) or by the alkali-detergent method described previously (Helting, T. (1971) J. Biol. Chem. 246, 815-822). The applicability of the salt-detergent procedure as a general method for solubilization of membrane-bound glycosyltransferases was tested by assay of four other glycosyltransferases involved in chondroitin sulfate synthesis (UDP-D-xylose:core protein xylosyltransferase, UDP-D-galactose:4-O-beta-D-galactosyl-D-xylose galactosyltransferase, UDP-D-glucuronic acid: 3-O-beta-D-galactosyl-D-galactose glucuronosyltransferase, and UDP-N-acetyl-D-galactosamine: (GlcUA-GalNAc-4-sulfate)4 N-acetylgalactosaminyltransferase). In each case, greater than 70% of the activity was solubilized and, on gel chromatography on Sephadex G-200, the enzymes appeared largely in included positions and partially separated from each other. After partial purification by gel chromatography on Sephadex G-200, UDP-D-galactose:D-xylose galactosyltransferase was purified further by chromatography on one of several affinity matrices, i.e. xylosylated core protein of cartilage proteoglycan coupled to CNBr-activated Sepharose, a core protein matrix saturated with UDP-D-xylose:core protein xylosyltransferase or UDP-D-xylose:core protein xylosyltransferase covalently bound to Sepharose. The specific activities of the enzyme preparations obtained by these procedures were approximately 1000-fold greater than that of the crude homogenate.
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PMID:Biosynthesis of chondroitin sulfate. Solubilization of chondroitin sulfate glycosyltransferases and partial purification of uridine diphosphate-D-galactose:D-xylose galactosyltrans. 115 Jun 55

Over half of the chloroplast ribosomes isolated from growing cultures of Chlamydomonas reinhardtii are bound to chloroplast thylakoid membranes if completion of nascent polypeptide chains is prevented by chloramphenicol. The free chloroplast ribosomes are recovered in homogenate supernatants, and presumably originate from the chloroplast stroma. Only about 10% of these free chloroplast ribosomes are polyribosomes, even under conditions when 70% of free cytoplasm ribosomes are recovered as polyribosomes. The nonionic detergent Nonidet P-40 liberates atypical polyribosomes (Type I), from membranes, which require both ribonuclease and proteases for complete conversion to monomeric ribosomes. Thus Type I particles are held together by mRNA but are also held together by peptide bonds. These Type I polyribosomes probably are not bound to intact membrane, but might be bound to some protein-containing sub-membrane particle. The Type I polyribosomes are dissociated to ribosomal subunits by puromycin and high salt, and contained 0.2 to 1 nascent chain per ribosome. If membranes are treated with Nonidet and proteases at the same time, polyribosomes which are digested to monomeric ribosomes by ribonuclease alone (Type II) are obtained. Type II polyribosomes are smaller than Type I, and probably represent the true size distribution of polyribosomes on the membranes. At least 50% of the membrane-bound ribosomes are polyribosomes, since that much membrane bound chloroplast RNA is recovered as Type I or Type II polyribosomes.
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PMID:Free and membrane-bound chloroplast polyribosomes Chlamydomonas reinhardtii. 116 19

D-beta-Hydroxybutyrate dehydrogenase of bovine heart mitochondria has been purified to apparent homogeneity. The membrane-bound enzyme is first released by phospholipase A digestion of the mitochondria. Lithium bromide, 0.4 M, is used to aid release, and dithiothreitol is required to stabilize the enzyme. The membranous material is removed by centrifugation, and the apoenzyme is recovered in the supernatant and precipitated with ammonium sulfate to 50 percent of saturation. The main purification (100-fold) is achieved by selective adsorption and elution on controlled pore glass beads. The purified enzyme has been purified approximately 250-fold from the mitochondria. The purified enzyme is homogeneous as shown by poly-acrylamide gel electrophoresis in sodium dodecyl sulfate or acid-urea systems; a sharp band is obtained which is equivalent to a subunit molecular weight of 31,500. The apoenzyme is devoid of lipid and is completely inactive as isolated. It can be reactivated by adding aqueous microdispersions of lecithin or phospholipids containing lecithin. The apoenzyme is stable, i.e. it has a half-life of about 450 hours at 0-2 degrees in 0.4 M lithium bromide, containing 5 mM dithiothreitol at pH 7, and is soluble at these conditions, existing mainly as a monomer and dimer in dilute solution. It has a tendency to associate into larger aggregates when the salt concentration is lowered. The enzyme does not have a distinctive amino acid composition as compared with other proteins or soluble dehydrogenases. The purified apodehydrogenase is well suited for study of specific protein-lipid interaction, as well as the molecular basis for the role of phospholipid in this lipid-requiring enzyme.
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PMID:Preparation of a homogeneous soluble D-beta-hydroxybutyrate apodehydrogenase from mitochondria. 117 Oct 99

Mild ribonuclease treatment of the membrane fraction of P3K cells released three types of membrane-bound ribosomal particles: (a) all the newly made native 40S subunits detected after 2 h of [3H]uridine pulse. Since after a 3-min pulse with [35S]methionine these membrane native subunits appear to contain at least sevenfold more Met-tRNA per particle than the free native subunits, they may all be initiation complexes with mRNA molecules which have just become associated with the membranes; (b) about 50% of the ribosomes present in polyribosomes. Evidence is presented that the released ribosomes carry nascent chains about two and a half to three times shorter than those present on the ribosomes remaining bound to the membranes. It is proposed that in the membrane-bound polyribosomes of P3K cells, only the ribosomes closer to the 3' end of the mRNA molecules are directly bound, while the latest ribosomes to enter the polyribosomal structures are indirectly bound through the mRNA molecules; (c) a small number of 40S subunits of polyribosomal origin, presumably initiation complexes attached at the 5' end of mRNA molecules of polyribosomes. When the P3K cells were incubated with inhibitors acting at different steps of protein synthesis, it was found that puromycin and pactamycin decreased by about 40% the proportion of ribosomes in the membrane fraction, while cycloheximide and anisomycin had no such effect. The ribosomes remaining on the membrane fraction of puromycin-treated cells consisted of a few polyribosomes, and of an accumulation of 80S and 60S particles, which were almost entirely released by high salt treatment of the membranes. The membrane-bound ribosomes found after pactamycin treatment consisted of a few polyribosomes, with a striking accumulation of native 60S subunits and an increased number of native 40S subunits. On the basis of the observations made in this and the preceding papers, a model for the binding of ribosomes to membranes and for the ribosomal cycle on the membranes is proposed. It is suggested that ribosomal subunits exchange between free and membrane-bound polyribosomes through the cytoplasmic pool of free native subunits, and that their entry into membrane-bound ribosomes is mediated by mRNA molecules associated with membranes.
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PMID:Membrane-bound ribosomes of myeloma cells. III. The role of the messenger RNA and the nascent polypeptide chain in the binding of ribosomes to membranes. 117 34

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