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At least 1,531 records · Page 85Linked to original sources
PubMed1972

The use of acid alumina and sephadex LH-20 for the separation and characterization of ethanol-soluble peptides produced by Bacillus brevis.

Cell extracts from Bacillus brevis (A.T.C.C. 10068), grown with various media, incorporated certain (14)C-labelled amino acids that are normally components of tyrothricin into material that was extracted by ethanol from the precipitate formed by adding acid. When this material was separated by paper and silica-gel thin-layer chromatography and paper electrophoresis (14)C was located in those regions that also contained gramicidin and tyrocidine. From a study of the properties of the system responsible for the incorporation it was deduced that non-tyrothricin materials were present. It was shown that the methods normally used to characterize tyrothricin do not adequately distinguish between tyrothricin and non-tyrothricin materials. However, a method for separating these materials was devised. This involved elution with ethanol from columns of acid alumina followed by gel filtration on Sephadex LH-20 with dimethylformamide-water solvent. The behaviour of gramicidin and tyrocidine on the Sephadex LH-20 column was examined, and it was concluded that the separation was not caused simply by gel filtration of unassociated molecules. Also, tyrocidine molecules with different amino acid compositions seemed to have different affinities for the Sephadex LH-20 column.

Aluminum↗
PubMed1974

Biological, proton-magnetic-resonance- and ultraviolet-spectroscopic evidence for a molecular complex of actinomycin D and 10,11-dihydro-3H-naphth (1,2-g)indazol-7-ol.

A proton-magnetic-resonance study of the complex formed between actinomycin D and 10,11-dihydro-3H-naphth[1,2-g]indazol-7-ol strongly suggests that the indazole lies above the phenoxazine ring of actinomycin D. The complex can be destroyed by addition of dimethyl sulphoxide or dimethylformamide. The actinomycin D-indazole complex inhibits growth of Pseudomonas fluorescens and raises the thermal denaturation response of DNA. These data support the hypothesis that a molecular complex is formed which readily inhibits cell growth and interacts with DNA.

Chemical Phenomena↗
PubMed1983

Chemical modification of Escherichia coli succinyl-CoA synthetase with the adenine nucleotide analogue 5'-p-fluorosulphonylbenzoyladenosine.

Escherichia coli succinyl-CoA synthetase (EC 6.2.1.5) was irreversibly inactivated on incubation with the adenine nucleotide analogue 5'-p-fluorosulphonylbenzoyladenosine (5'-FSBA). Optimal inactivation by 5'-FSBA took place in 40% (v/v) dimethylformamide. ATP and ADP protected the enzyme against inactivation by 5'-FSBA, whereas desulpho-CoA, an analogue of CoA, did not. Inactivation of succinyl-CoA synthetase by 5'-FSBA resulted in total loss of almost four thiol groups per alpha beta-dimer, of which two groups appeared to be essential for catalytic activity. 5'-FSBA at the first instance appeared to interact non-specifically with non-essential thiol groups, followed by a more specific reaction with essential thiol groups in the ATP(ADP)-binding region. Plots of the data according to the method of Tsou [(1962) Sci. Sin. 11, 1535-1558] revealed that, of the two slower-reacting thiol groups, only one was essential for catalytic activity. When succinyl-CoA synthetase that had been totally inactivated by 5'-FSBA was unfolded in acidic urea and then refolded in the presence of 100 mM-dithiothreitol, 85% of the activity, in comparison with the appropriate control, was restored. These data are interpreted to indicate that inactivation of succinyl-CoA synthetase by 5'-FSBA involves the formation of a disulphide bond between two cysteine residues. Disulphide bond formation likely proceeds via a thiosulphonate intermediate between 5'-p-sulphonylbenzoyladenosine and one of the reactive thiol groups of the enzyme.

Adenosine↗
PubMed1986

Determination of gangliosides as 2,4-dinitrophenylhydrazides by high-performance liquid chromatography.

A specific, sensitive and easily performed method for the determination of gangliosides in tissue was developed. After removal of water-soluble compounds, total lipids were extracted from tissue and then treated with 2,4-dinitrophenylhydrazine hydrochloride and dicyclohexylcarbodi-imide in dimethylformamide at 0 degrees C to form ganglioside hydrazides. After removal of excess reagents by column chromatography on silicic acid, the ganglioside 2,4-dinitrophenylhydrazides were eluted from the column and analysed by h.p.l.c. with the use of a silica-gel normal-phase column eluted with an isocratic chloroform/methanol/water/acetic acid system. The addition of CaCl2 improved the separation of GM3 ganglioside containing N-acetylneuraminic acid from that containing N-glycollylneuraminic acid. 2,4-Dinitrophenylhydrazide peaks were measured by the absorbance at 342 nm. Quantification of GM3, GM2, GM1, GD1a, GD1b, GT1b and LM1 gangliosides was linear in a range 0.02-1.6 nmol. GM4, GD3, GT1a and GQ1b gangliosides also yielded distinct peaks, although the range of linearity was not examined. This method was applied to the analysis of the total lipids of rat brain and hepatocytes.

Animals↗
PubMed1992

Variation in the P2-S2 stereochemical selectivity towards the enantiomeric N-acetylphenylalanylglycine 4-nitroanilides among the cysteine proteinases papain, ficin and actinidin.

1. Values of the kinetic specificity constant, kcat./Km, for the hydrolysis of N-acetyl-L-phenylalanylglycine 4-nitroanilide (I) and of its D-enantiomer (II) catalysed by ficin (EC 3.4.22.3) and by actinidin (EC 3.4.22.14) at pH 6.0, I 0.1 mol/l, 8.3% (v/v) NN-dimethylformamide and 25 degrees C were determined by using initial-rate data with [S] much less than Km and weighted nonlinear regression analysis as: for ficin, (kcat./Km)L = 271 +/- 6 M-1.s-1, (kcat./Km)D = 2.9 +/- 0.1 M-1.s-1, and for actinidin (kcat./Km)L = 13.3 +/- 0.7 M-1.s-1, (kcat/Km)D = 0.34 +/- 0.01 M-1.s-1.2. These data and analogous values for the corresponding reactions catalysed by papain (EC 3.4.22.2), (kcat./Km)L = 2064 +/- 31 M-1.s-1, (kcat./Km)D = 5.5 +/- 0.1 M-1.s-1, demonstrate marked variation in stereochemical selectivity for substrates (I) and (II) among the three cysteine proteinases with the following values for the index of stereochemical selectivity Iss = (kcat./Km)L/(kcat./Km)D: for papain, 375; for ficin 93; for actinidin 39. 3. Model building suggests ways in which, for the papain-catalysed reactions, binding interactions involving the extended acyl groups of the substrates may need to change as the reaction proceeds from adsorptive complex (ES) to tetrahedral intermediate (THI) before its rate-determining, general acid-catalysed collapse to acylenzyme intermediate. In particular, satisfactory alignment in the catalytic site at the THI stage of the acylation process appears to demand rotation of the substrate moiety about its long axis. 4. The different consequences of this rotation for the L- and D-enantiomers suggest that for closely related systems the greater the extent of this rotational adjustment the greater would be the value of Iss.5. For the actinidin-substrate combinations, model building suggests that even at the ES complex stage of catalysis it is not possible to approach optimized P2-S2 contacts and the three hydrogen-bonding interactions deduced for papain-ligand complexes in the absence of significant movement of protein conformation. Possible binding modes in which some of the interactions deduced for papain are relaxed are discussed. Consideration of postulated binding modes in the various transition states is shown to account for the order of reactivity reflected in values kcat./Km for the four reactions involving papain (Pap) and actinidin (Act) with the L- and D-enantiomeric substrates: Pap-L much greater than Act-L greater than Pap-D much greater than Act-D.(ABSTRACT TRUNCATED AT 400 WORDS)

Anilides↗
PubMed1993

Effect of selective thiol-group derivatization on enzyme kinetics of (R)-3-hydroxybutyrate dehydrogenase.

(R)-3-Hydroxybutyrate dehydrogenase (BDH) is a phosphatidylcholine-requiring tetrameric enzyme with two thiol groups (SH-1 and SH-2) per protomer. By first protecting the more rapidly reacting thiol group (SH-1) with diamide [1,1'-azobis-(NN'-dimethylformamide), DM] to form DM(SH-1)BDH, SH-2 can be selectively derivatized by reaction with maleimide reagents such as 4-maleimido-2,2,6,6-tetramethyl-piperidine-N-oxyl (MSL), which gives DM(SH-1)MSL(SH-2)BDH. Reduction with dithiothreitol (DTT) regenerates SH-1, yielding MAL(SH-2)BDH (where MAL is the diamagnetic reduction product of MSL-BDH and DTT). The enzymic activity of DM(SH-1)BDH is decreased to approx. 4% relative to the native purified enzyme, and the apparent Km for substrate, KmBOH, is increased approx. 100-fold. Reduction of DM(SH-1)BDH with DTT regenerates SH-1 and restores normal enzymic function. Modification of SH-2 with piperidinylmaleimide [MAL(SH-2)BDH] diminishes enzymic activity to approx. 35% of its original value, but has no significant effect on apparent KmBOH. The doubly derivatized enzyme, DM(SH-1)MSL(SH-2)BDH, has lower enzymic activity [about half that for DM(SH-2)BDH] and a yet higher apparent KmBOH than DM(SH-1)BDH. Derivatization of SH-2 with different maleimide reagents results in diminished activity approximately proportional to the size of the maleimide substituent, suggesting that this inhibition is steric. Whereas modification of SH-1 results in marked changes in kinetic parameters (increased apparent Km and reduced apparent Vmax), derivatization of SH-2 has a lesser effect on enzymic function. Thus SH-1 is postulated to be closer to the active centre than is SH-2, although neither is involved in catalysis, since: (1) the activity of the derivatized enzyme is not abolished; and (2) activity can be enhanced by increasing substrate (and cofactor) concentrations.

Animals↗
PubMed1995

Regulation of hepatocyte plasma membrane alpha 1-adrenergic receptors by 4 beta-phorbol 12-myristate 13-acetate.

The effect of phorbol 12-myristate 13-acetate (PMA) on hepatocyte alpha 1-adrenergic receptors was determined by [3H]prazosin binding to plasma membranes from control and PMA-treated hepatocytes. Membranes from hepatocytes incubated with PMA (1 microgram/ml) for 1 h exhibited a 40% decrease in alpha 1-adrenergic receptors (481 +/- 10 fmol/mg of protein; mean +/- S.E.M. for three separate experiments) relative to vehicle-treated (dimethylformamide) hepatocytes (802 +/- 91 fmol/mg of protein; n = 3), with no significant effect on the KD. The PMA-induced decrease in alpha 1-adrenergic receptors was maximal by 30 min and half-maximal inhibition of [3H]prazosin binding occurred with a PMA concentration of approx. 15 ng/ml. Pretreatment of hepatocytes with staurosporine (5 microM) blocked the effect of PMA, and 4 beta-phorbol 13-monoacetate was ineffective, suggesting the involvement of protein kinase C (PKC). Treatment of hepatocytes with primaquine (300 microM) for 15 min decreased hepatocyte plasma membrane alpha 1-adrenergic receptors by 34.0 +/- 2.4% (mean +/- S.E.M. of three experiments). Removal of primaquine allowed essentially complete recovery (98 +/- 4%; mean +/- S.E.M. for five separate experiments) of plasma membrane [3H]prazosin binding within 20 min, suggesting that the alpha 1-adrenergic receptor undergoes endocytotic recycling. Addition of PMA (1 microgram/ml) to hepatocytes immediately after removal of primaquine, completely inhibited the increase in plasma membrane alpha 1-adrenergic receptors relative to control cells, but had no effect on hepatocytes whose cell surface alpha 1-receptors remaining after primaquine treatment had been inactivated by alkylation. These observations suggested that activation of PKC may facilitate the internalization of the alpha 1-adrenergic receptor in hepatocytes.

Animals↗
PubMed2002

Differentiation of PLB-985 myeloid cells into mature neutrophils, shown by degranulation of terminally differentiated compartments in response to N-formyl peptide and priming of superoxide anion production by granulocyte-macrophage colony-stimulating factor.

Mature blood neutrophils have a short lifespan in vitro and are not easily transfectable. We obtained terminally mature neutrophils after differentiation of immature transfectable PLB-985 myeloid cells by treatment with dimethylformamide (0.5%), Nutridoma SP (1%) and fetal calf serum (0.5%). Maturation was shown by functional degranulation, in response to bacterial N-formyl peptide (fMLP), of specific granules and secretory vesicle contents; the latter emerge during the last step of normal neutrophil differentiation into bone marrow. These differentiated cells also produced quantities of superoxide anion similar to those produced by blood neutrophils, in response to physiological stimuli (fMLP); in addition, the fMLP-induced respiratory burst was primed by the proinflammatory cytokine granulocyte-macrophage colony-stimulating factor. Thus, in our experimental conditions, PLB-985 cells transformed into fully differentiated neutrophils capable of fine regulation by inflammatory agents. This cell model will help in the understanding of the molecular mechanisms underlying neutrophil functions.

Calcium↗
PubMed1999

A method for the preparation of Tetrahymena thermophila phospholipase A1 suitable for large-scale production.

A rapid and economical method for the purification of phospholipase A1 (PLA1) from the extracellular medium of the ciliate Tetrahymena thermophila is presented. Essentially, the procedure, here designated as purification by selective interaction (PSI), entails the incubation of media containing PLA1 with liposomes made of soy bean phospholipids. The PLA1-lipid complexes are precipitated by the addition of CaCl2 and collected by centrifugation. Elution of the PLA1 is effected by treating the complexes with 40% dimethylformamide, a reversible inhibitor of this enzyme, which is easily removed by dialysis. In combination with DEAE cellulose ion exchange chromatography, PSI yielded homogeneous PLA1 preparations with a 14% recovery and a 416-fold increase in specific activity. This procedure, which can be completed within 1 day, may prove useful for the isolation of phospholipases from other sources. This practical method for the purification of a microbial PLA1 opens the way to large-scale production of these types of enzyme, which are not as yet commercially available.

Animals↗
PubMed1999

Purification and characterization of a highly enantioselective epoxide hydrolase from Aspergillus niger.

The epoxide hydrolase from Aspergillus niger was purified to homogeneity using a four-step procedure and p-nitrostyrene oxide (pNSO) as substrate. The enzyme was purified 246-fold with 4% activity yield. The protein is a tetramer composed of four identical subunits of molecular mass 45 kDa. Maximum activity was observed at 40 degrees C, pH 7.0, and with dimethylformamide as cosolvent to dissolve pNSO. Hydrolysis of pNSO was highly enantioselective, with an E value (i.e. enantiomeric ratio) of 40 and a high regioselectivity (97%) for the less hindered carbon atom of the epoxide. This enzyme may be a good biocatalyst for the preparation of enantiopure epoxides or diols.

Amino Acid Sequence↗
PubMed2000

A novel NADPH:diamide oxidoreductase activity in arabidopsis thaliana P1 zeta-crystallin.

The zeta-crystallin (ZCr) gene P1 of Arabidopsis thaliana, known to confer tolerance toward the oxidizing drug 1,1'-azobis(N, N-dimethylformamide) (diamide) to yeast [Babiychuk, E., Kushnir, S., Belles-Boix, E., Van Montagu, M. & Inzé, D. (1995) J. Biol. Chem. 270, 26224], was expressed in Escherichia coli to characterize biochemical properties of the P1-zeta-crystallin (P1-ZCr). Recombinant P1-ZCr, a noncovalent dimer, showed NADPH:quinone oxidoreductase activity with specificity to quinones similar to that of guinea-pig ZCr. P1-ZCr also catalyzed the divalent reduction of diamide to 1,2-bis(N,N-dimethylcarbamoyl)hydrazine, with a kcat comparable with that for quinones. Two other azodicarbonyl compounds also served as substrates of P1-ZCr. Guinea-pig ZCr, however, did not catalyze the azodicarbonyl reduction. Hence, plant ZCr is distinct from mammalian ZCr, and can be referred to as NADPH:azodicarbonyl/quinone reductase. The quinone-reducing reaction was accompanied by radical chain reactions to produce superoxide radicals, while the azodicarbonyl-reducing reaction was not. Specificity to NADPH, as judged by kcat/Km, was > 1000-fold higher than that to NADH both for quinones and diamide. N-Ethylmaleimide and p-chloromercuribenzoic acid inhibited both quinone-reducing and diamide-reducing activities. Both NADPH and NADP+ suppressed the inhibition, but NADH did not, suggesting that sulfhydryl groups reside in the binding site for the phosphate group on the adenosine moiety of NADPH. The diamide-reducing activity of P1-ZCr accounts for the tolerance of P1-overexpressing yeast to diamide. Other possible physiological functions of P1-ZCr in plants are discussed.

Amino Acid Sequence↗
PubMed1988

Modified syntheses of dopamine-4-sulfate, epinephrine-3-sulfate, and norepinephrine-3-sulfate: determination of the position of the sulfate group by 1H-NMR spectroscopy.

With respect to the growing interest in sulfoconjugated catecholamines (CAS), reliable syntheses of those substances including high purification and unequivocal identification are required. For the syntheses of the 3-O-sulfates of norepinephrine (NE) and epinephrine (EPI), modifications of the methods of Stolz (12) and Arakawa et al. (1) were performed. Noradrenalone and adrenalone were prepared according to the method of Stolz (12) and sulfated by reaction with pyridine-sulfurtrioxide complex in dry pyridine at 60 degrees C. After reduction of these ketosulfates by sodium borohydride in dry pyridine, NE-3-O-S and EPI-3-O-S were obtained respectively. We synthesized dopamine-4-O-sulfate (DA-4-O-S) by reaction of DA hydrochloride with pyridine-sulfurtrioxide complex in dry dimethylformamide at 20 degrees C (Harbeson et al., 1983). The highly purified products (DA-4-O-S, NE-3-O-S, EPI-3-O-S) were characterized by their melting points (mp), infrared spectra (IR), thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), elemental analysis, and 1H-nuclear magnetic resonance spectroscopy (1H-NMR).

Dopamine↗
PubMed2006

Complete mapping of the morphologies of some linear and graft fluorinated co-oligomers in an aprotic solvent by dissipative particle dynamics.

The mesoscopic morphologies of linear and graft fluorinated block copolymers of ABCBA and C:BA types, respectively, have been investigated by using dissipative particle dynamics method. Self-assembly in a selective solvent has been examined by the introduction of dimethylformamide as the choice of solvent. By comparing the solubility parameters calculated using atomistic simulations, fluorine-containing segments are found to be immiscible both with other segments of the polymer and with the solvent. Morphologies of the pure linear and graft copolymers were lamellar and cylindrical, respectively. Interfacial tension versus concentration curves have been used to explain the self-assembly behavior of copolymers in solution, as well as to predict the kinetic mechanisms responsible for this behavior.

Journal Article↗
PubMed2006

Prediction among different spectroscopic properties for aqueous systems.

Spectroscopic properties obtained by NMR and vibrational spectra both reflect the microscopic environment of solutions, and the local composition (LC) theory can be used to study environmental effects on spectroscopic properties. Based on the LC model, the relationship between NMR and vibrational spectra, including infrared (IR) spectroscopy and Raman, were investigated. For the aqueous systems-water+N, N-dimethylformamide, water+acetone, water+methanol, and water+ethanol, we performed prediction between concentration-dependent peak positions of IR and Raman, as well as between concentration-dependent vibrational properties and 1H NMR chemical shifts. The results showed that reliable prediction could be achieved with the help of the LC model. This suggests that 1H NMR chemical shifts and vibrational spectroscopic properties may tell us the same story about the local environment encountered in solution.

Journal Article↗
PubMed2006

A comparative study of the properties of polar and nonpolar solvent/solute/polystyrene solutions in microwave fields via molecular dynamics.

The influence of an applied microwave field on the dynamics of methylamine-dichloromethane (DCM) mixtures bound within atactic polystyrene (a-PS) over a range of polymer densities from 30 to 94 wt % polymer was examined using atomistic molecular dynamics simulations. This study is an extension of previous studies on methylamine transport in relatively polar polystyrene solutions of methanol and dimethylformamide [M. J. Purdue et al., J. Chem. Phys. 124, 204904 (2006)]. A direct comparison is made across the three types of polystyrene solutions. Consideration is given to both solvent and reagent transport within the polymer solutions under zero-field conditions and in an external electromagnetic field in the canonical ensemble (NVT) at 298.0 K. Various frequencies up to 10(4) GHz and a rms electric field intensity of 0.1 VA were applied. The simulation studies were validated by comparison of the simulated zero-field self-diffusion coefficients of DCM in a-PS with those obtained using pulsed-gradient spin-echo NMR spectrometry. Athermal effects of microwave fields on solute transport behavior within polymer solutions are discussed.

Journal Article↗
PubMed1975

Induction of erythroid differentiation in murine virus infected eythroleukemia cells by highly polar compounds.

Murine-virus-infected erythroleukemia cells cultured in a medium with dimethylsulfoxide or N,N-dimethylformamide are induced to differentiate to erythroid cells. A number of highly polar compounds have a similar effect in inducing erythroid differentiation of the virus-infected cells, as assayed by the appearance of hemoglobin. These compounds are 1-methyl-1-2-piperidone, N,N-dimethylacetamide, N-methylpyrrolidinone, N-methylacetamide, 2-pyrrolidinone, propionamide, pyridine-N-oxide, piperidone, N-methylformamide, acetamide, and triethylene glycol. It has been previously reported that dimethylsulfoxide must be present during DNA synthesis and, possibly, shortly therafter, to induce differentiation. These findings are consistent with the hypothesis that dimethylsulfoxide and related polar compounds act by changing the conformation of DNA or a DNA-protein complex, causing an alteration in transcription that leads to the expression of the program of erythroid differentiation.

Acetamides↗
PubMed1983

Total synthesis of human beta-lipotropin.

The total synthesis of human beta-lipotropin has been accomplished by the new segment-coupling method in aqueous solution. The peptides Ac-Arg-beta-lipotropin-(61-89) (I) and [GlyS60]-beta-lipotropin-(1-60) (II) were synthesized by the solid-phase method. Reaction of peptide I with citraconic anhydride followed by brief digestion with trypsin to remove the acetylarginyl group, gave Ia. Reaction of peptide II with citraconic anhydride gave the citraconyl peptide IIa. Ia and IIa were coupled together in 50% dimethylformamide by reaction with silver nitrate/N-hydroxysuccinimide. After removal of the citraconyl groups in 25% acetic acid, a 10% yield of synthetic beta-lipotropin could be isolated. The synthetic product was shown to be identical to native human beta-lipotropin by paper electrophoresis, isoelectric focusing, HPLC, lipolytic activity in isolated rabbit fat cells, and radioimmunoassay.

Amino Acid Sequence↗
PubMed1985

Driving force and nucleophilicity in S(N)2 displacements.

The free energies of activation for reaction of six anionic nucleophiles with methyl iodide in dimethylformamide correlate linearly with the overall heats of reaction in the gas phase. The result indicates that nucleophilicity in this S(N)2 displacement reaction is dominated by electron affinity and bond-strength effects.

Journal Article↗