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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The initial rates of transport of uridine, thymidien, purines, choline and 2-deoxy-D-glucose by cultured Novikoff rat hepatoma cells were determined as a function of temperature between 5 and 41 degrees C. Arrhenius plots of all transport systems exhibited sharp breaks in slope; between 17 and 23 degrees for uridine, thymidine and hypoxanthine-guanine transport and between 29 and 32 degrees for choline and 2-deoxy-D-glucose transport. The activation energies for the transport systems changed from 15-26 kcal/mole below the transition temperatures to 4-9 kcal/mole above the transition temperatures. Propagation of the cells in the presence of cis-6-octadecenoic acid which results in marked changes in the lipid composition of cell membrane, had little effect on the temperature characteristics of the various transport systems. Similarly, propagation of the cells for 24 hr in media containing Tween 40 or nystatin had no effect on the capacity of the cells to transport the various substrates or on the temperature dependence of the transport systems. The presence of ethanol, phenethyl alcohol or Persantin at concentrations that inhibited thymidine and 2-deoxy-D-glucose transport between 40 and 70% also did not alter the transition temperatures or activation energies for the transport of these substrates. Cytochalasin B, on the other hand, shifted the transition temperature for 2-deoxy-D-glucose transport to higher temperatures in a concentration-dependent manner, whereas it had no effect on the temperature dependence of thymidien transport.
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PMID:Temperature-dependent changes in activation energies of the transport systems for nucleosides, choline and deoxyglucose of cultured Novikoff rat hepatoma cells and effects of cytochalasin B and lipid solvents. 5 43

The aglycone of the nucleoside antibiotic, bredinin, was as strongly cytotoxic to L5178Y cells as bredinin. The cytotoxic properties of the aglycone were very similar to those of bredinin and the minimum inhibitory concentrations of both were 10(-5)M. The growth inhibitory effects of both agents regardless of their concentrations, were reversed by guanylic acid, guanosine or guanine. However, on increasing the concentrations of these agents, the reversing effect of guanylic acid decreased gradually, the dose-response curves for the two agents being similar. Both agents inhibited the incorporation of thymidine and uridine, but not leucine into macromolecules in L5178Y cells and their inhibitory effects were reversed to similar extents by guanylic acid. On the other hand, the growth inhibitory effect of the aglycone on L5178Y cells was prevented by adenine only, though not be adenosine or adenylic acid while the effect of bredinin was not prevented by adenine. These results suggest that the aglycone itself does not inhibit growth, but that its effect is due to its conversion to bredinin by an enzyme such as adenine phosphoribosyl transferase. For recovery of growth, three moles of adenine were required per mole of the aglycone. When the aglycone was administered orally to rats, bredinin was administered orally to rats, bredinin was recovered in their serum and urine.
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PMID:Effect of bredinin and its aglycone on L5178Y cells. 17 Dec 46

Uridine nucleosidase (EC 3.2.2.3) was purified from commercial bakers' yeast to homogeneity, as judged by a single band observed on polyacrylamide disc gel electrophoresis. The molecular weight of the enzyme, estimated by gel filtration, was approximately 32,500. Polyacrylamide electrophoresis in 0.2% sodium dodecyl sulfate showed the presence of two apparently identical subunits of 17,000 molecular weight. The amino acid composition indicated a large excess of glutamic acid and aspartic acid over other amino acid residues and a very low content of tyrosine and tryptophan. Th SH groups analysis performed with 5,5'-dithiobis (2-nitrobenzoic acid) on thenative protein as well as in the presence of 1% sodium dodecyl sulfate showed the existence of one sulfhydryl group per mole of enzyme. Uridine nucleosidase is active on uridine and 5-methyluridine (ribosylthymine) resulting inactive toward all other pyrimidine and purine nucleosides tested. The Km values for uridine and 5-methyluridine were 0.86 x 10(-3) M and 1.66x10--3M, respectively. The optimal pH is around 7.0. The isoelectric point is 5.1. Among a variety of compounds tested only ribose and glucose 6-phosphate were inhibitory and Ki values were 7.2 mM and 0.19 mM, respectively. Furthermore, ribosylthymine competitively inhibited the hydrolysis of uridine. The type of all inhibitions was competitive and the n' values of the Hill plots were near 1. The effect of temperature on the enzyme activity plotted accoring to Arrhenius gave a value of E = 4740 cal per mole. The enzyme in 100 mM phosphate, pH = 7.0, is stable at 4 degrees for 15 days without any loss of activity.
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PMID:Bakers' yeast uridine nucleosidase. Purification, composition, and physical and enzymatic properties. 23 97

HeLa cell heterogeneous nuclear RNA derived from high-molecular-weight nuclear ribonucleoprotein (RNP) particles contains oligo(U) sequences of 15-50 nucleotides base-paired with poly(A). These duplexes are resistant to pancreatic RNase at 0.5 M NaCl in native RNP, remain so after chemical deproteinization of the RNP digests, and then copurify with poly(A) on oligo(dT)-cellulose chromatography. Oligo(dT)-cellulose binding capacity of the oligo(U)-poly(A) duplexes is abolished by prior titration of the nonduplex poly(A) regions with excess poly(U). The oligo(dT)-purified fraction is 97.5 mole % A + U and the [3H]uridine-labeled component is resistant to redigestion by pancreatic RNase at 0.5 M NaCl but not at 0.01 M NaCl. After thermal denaturation, the [3H]uridine-labeled chains become RNase-sensitive at 0.5 M NaCl. Electrophoresis of [3H]adenosine- or [3H]uridine-labeled material in polyacrylamide gels containing 99% formamide confirms that the oligo(U) sequences are not covalently linked to poly(A). Controls establish that the A-U duplexes are not formed artifactually during isolation of heterogeneous nuclear RNP or subsequent fractionation. The oligo(U)-poly(A) duplexes appear to be associated with protein in native heterogeneous nuclear RNP, as reflected by the differential pancreatic RNase sensitivity of the duplexed oligo(U) in RNP (resistant) and RNA (sensitive), measured at physiological ionic strength.
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PMID:Heterogeneous nuclear RNA secondary structure: oligo (U) sequences base-paired with poly (A) and their possible role as binding sites for heterogeneous nuclear RNA-specific proteins. 26 83

An unusual class of wheat germ tRNAs has been isolated which completely lacks ribothymidine (rT) and contains an unmodified uridine in its place. We discuss here the isolation, identification and properties of these tRNAs. The rT-lacking tRNAs of wheat germ are essentially limited to the glycine isoacceptors (a minimum of five identifiable species), three threonine and at least, one tyrosine tRNA. All tRNAs were obtained 70-100% pure by chromatographic methods, and were detected by their ability to be methylated by E. coli rT-forming uracil methyltransferase with methyl-labeled S-adenosyl-L-methionine (SAM) as the methyl donor. In vitro methylation of each of the tRNAs resulted in the formation of 1 mole of rT per mole of tRNA. In the one case analyzed in detail (tRNA1Gly), all of the rT was found to be located at the 23rd position from the 3' end of the tRNA molecule. Following complete digestion of four highly purified glycine isoacceptors (tRNAGly1,4,5,6) to nucleosides and subsequent periodate oxidation and 3H potassium borohydride reduction, all were found to contain an unusually high level of 5-methylcytidine (m5C) (3-4 residues per molecule), and all contained no rT. The possible correlation between the presence of m5C and the absence of rT is discussed. All of the chromatographically purified glycine tRNAs function in a wheat germ cell-free protein synthesizing system and polymerize glycine in response to either poly G or poly (G, U).
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PMID:Wheat germ tRNAs containing uridine in place of ribothymidine: a characterization of an unusual class of eukaryotic tRNAs. 65 15

High-resolution liquid-chromatographic methods developed for analyzing nucleotide pools at the nanogram level in four representative species of ascomycetes (Penicillium citrinum, Aspergillus niger, Fusarium moniliforme, and Cladosporium herbarum) were used to study polysaccharide biosynthesis. Nucleotides extracted from the mycelial mat were preseparated from interfering polysaccharides, glycoproteins, and nucleic acids on a column of Biogel P-2. Resolution of 18 nucleotides from each fungal species was accomplished on AS-Pellionex-SAX, pellicular anion-exchanger by using a high-pressure liquid chromatograph. Nucleotides were identified by comparing peak retention-times, by differential u.v. absorption with two detectors in series at selected wavelengths, and by acid or enzymic hydrolysis with product identification by liquid chromatography. Pyrimidine bases exceeded purines by at least three fold, and uridine nucleotides often constituted 60-80 mole percent of the total nucleotides; extractable cytidine nucleotides were negligible. Uridine 5'-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl disphosphate) is the preponderant nucleotide throughout the growth cycles of all four species, amounting to 30-60% of all nucleotides present. For all four fungal species, a burst of nucleotide formation was observed after the first 48h (15-30 mumol/g tissue), with fluctuations that eventually fell to 0.1 mumol/g on the tenth day.
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PMID:High-pressure liquid-chromatographic assay of nucleotide-pool concentrations during polysaccharide biosynthesis in four ascomycetes. 91 96

We describe an assay for light microscopic visualization of specific glycosyltransferases on tissue sections or on cells. The assay uses a sequence of enzyme reactions that yields two moles of NADH for each mole of the uridine-5'-diphosphate (UDP) released during transfer of a monosaccharide from a UDP sugar to an acceptor. When diaphorase and tetrazolium salts are present in the incubation mixture, the tetrazolium salts are reduced to colored diformazans, which precipitate at the sites of glycosyltransferase activity. The validity of the assay was established by applying the technique to spermatozoa and liver, in which some glycosyltransferases have previously been localized. When suspensions of mouse spermatozoa were assayed for galactosyltransferase (GalTase) activity, diformazan precipitates appeared on the plasma membranes overlying the anterior heads of the spermatozoa, in agreement with immunochemical localizations. In mouse liver slices assayed with bilirubin as acceptor for glucuronyltransferase (GluTase) activity, dense diformazan deposits appeared on the hepatocytes but not on endothelial cells, also in agreement with immunochemical data. In the absence of acceptor or UDP sugar donor, diformazan deposits were minimal and random in all tissues tested. The assay's versatility was tested by incubating tissues with different sugar donors and acceptors to localize other sites of transferase activity. In mouse frozen liver sections, GalTase activity occurred in both hepatocytes and endothelial cells; in sections of rat submaxillary glands, GalTase activity was detected in mast cells. In liver sections, GlcuTase activity with o-aminophenol as acceptor was located primarily on the endothelial cells. With the appropriate sugar donor and acceptor, this assay should detect any transferase, other than the glucosyltransferases, that utilizes UDP sugars.
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PMID:Light microscopic localization of glycosyltransferase activities in cells and tissues. 210 33

A lysine-reactive cross-linker has been coupled to the minor base 3-(3-amino-3-carboxypropyl)uridine in the variable loop of the Escherichia coli elongator methionine tRNA (tRNA(mMet]. Incubation of the derivatized tRNA with E. coli methionyl-tRNA synthetase (MetRS) resulted in covalent coupling of the protein and nucleic acid and loss of amino acid acceptor activity of the enzyme. One mole of tRNA was cross-linked per mole of enzyme inactivated. Enzyme activity was largely restored by release of the bound tRNA following cleavage of the disulfide bond in the cross-linker with a sulfhydryl reagent. The cross-linking reaction was effectively inhibited by unmodified tRNA(mMet) but not by noncognate tRNA(Phe). The covalent complex was digested with trypsin, and the resulting tRNA-bound peptides were isolated by anion-exchange chromatography. The cross-linked peptides were released from the tRNA by cleavage in the disulfide bond of the cross-linker and purified by reverse-phase high-pressure liquid chromatography, yielding one major peptide plus several minor peptides. Amino acid analysis indicated that the major product was an octadecapeptide cross-linked to tRNA(mMet) through lysine residue 596 in the primary sequence of MetRS. The N-terminal sequence of the peptide was determined to be Val-Ala-Leu-Ile-Glu-Asn-Ala-Glu-Phe-Val, corresponding to residues 582-591 in MetRS. The procedures described here should be applicable to the determination of peptide sequences near the variable loop of other tRNAs containing the 3-(3-amino-3-carboxypropyl)uracil base when such tRNAs are bound to specific proteins.
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PMID:Covalent coupling of the variable loop of the elongator methionine tRNA to a specific lysine residue in Escherichia coli methionyl-tRNA synthetase. 310 75

The preparation of cytoplasmic membranes from suspensions of Staphylococcus aureus lysed by an enzyme recently isolated in these laboratories is described. These membranes contained: protein, 34.4%; ribonucleic acid, 6.6%; lipids, 34.5%; and total phosphorus, 1.4%. Such membranes exhibited adenosine 5'-triphosphatase (E.C. 3.6.1.3) activity, liberating orthophosphate at an initial rate of 0.53 mumole per min per mg of protein under optimal conditions. The enzyme was Mg(++)-dependent and K(+)- or Na(+)-stimulated. Maximal activity was observed with a molar adenosine 5'-triphosphate (ATP) to Mg(++) ratio of 1. One mole of orthophosphate was liberated per mole of ATP; the other product of digestion was adenosine 5'-diphosphate. Inorganic pyrophosphate and the 5'-triphosphates of guanosine, uridine, and cytidine were also attacked by membrane preparations, but more slowly than ATP. Ouabain, p-chloromercuribenzoate, and 2,4-dinitrophenol did not alter adenosine triphosphatase activity, whereas both Atebrine and chlorpromazine were inhibitory.
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PMID:Adenosine triphosphatase in isolated membranes of Staphylococcus aureus. 423 Aug 57

Isolated cell envelopes of a marine bacterium, M.B.3, have been prepared which possess a nonspecific, cation-activated nucleotidase. The cell envelope comprises approximately 35% (dry weight) of the whole cell and contains protein, 60.2%; lipids, 20.7%; hexose, 3.4%; and ribonucleic acid, 4.6%. No deoxyribonucleic acid could be detected in the preparations. The nucleotidase has an essential requirement for Mg(2+); maximum activation at pH 8.0 occurs at a divalent cation concentration of approximately 80 mm. At a Mg(2+) to adenosine 5'-triphosphate (ATP) ratio of 2:1, the enzyme was further stimulated by monovalent cations Na(+), K(+), NH(4) (+), and Li(+). Maximum activity was found at a monovalent ion concentration of approximately 0.3 m. The envelope preparation liberated inorganic orthophosphate (P(i)) from ATP, adenosine 5'-diphosphate (ADP), and adenosine 5'-monophosphate (AMP) at similar rates. Thin-layer and ion-exchange chromatography show that when AMP, ADP, and ATP were utilized as substrate, approximately 1, 2, and 3 moles of P(i), respectively, were produced per mole of adenosine. P(i) was also liberated from the 5'-triphosphates of guanosine, uridine, and cytidine. The enzyme preparation did not attack p-nitrophenyl phosphate, beta-glycerophosphate, or inorganic pyrophosphate. Sulfhydryl inhibitors p-chloromercuribenzoate, N-ethyl maleimide, and iodoacetate had little effect upon the nucleotidase activity. Ca(2+) and ethylenediaminetetraacetic acid caused complete inhibition of the system, whereas ouabain had no effect upon the enzyme activity. The concentrations of Na(+) (0.3 m) and Mg(2+) ions (60 to 80 mm) required for maximum ATP-hydrolyzing activity were similar to those concentrations necessary for maintenance of cell integrity and for the prevention of cell lysis.
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PMID:Cation-activated nucleotidase in cell envelopes of a marine bacterium. 537 Feb 80


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