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Query: UNIPROT:Q9UMR3 (NMR)
 150,598 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A study has been made of the association and the temperature-dependent conformation of adenosine 3',5'-monophosphate (cyclic AMP) in a neutral aqueous (2H2O) solution by means of proton magnetic resonance chemical shift and relaxation. The concentration and temperature-dependent chemical shifts of H(1'), H(2), and H(8), have enabled us to estimate the self-association constant, Ka = 1.1 +/- 0.3 M-1 at 25 degrees C and thermodynamic parameters delta H = -5.8 +/- 1.5 kcal/mol and delta S (25 degrees C) = -19.0 +/- 3 cal/mol per degree. The NMR-DESERT (Deuterium Substitution Effect on Relaxation Times) method has been utilized for the determination of the syn-anti conformational equilibrium in the monomeric state and for the determination of the mutual orientation of the two adenine rings in the dimeric state of cyclic AMP. The molecules were found to coexist with nearly equimolarity or syn-anti conformers and thermal activation of the molecules perturbs the syn-anti conformational equilibrium to comprise the syn form in preference at higher temperature. The glycosidic isomerization (from anti to syn) was found to be characterized both by a positive enthalpy change and by a positive entropy change. The cyclic AMP molecules prefer to take a 'trans-stacking' conformation in the dimeric state where the two molecules are arranged in such a way that the H(2) of one molecule is close to the H(8) of the other.
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PMID:Conformation of adenosine 3',5'-monophosphate in solution as studied by the NMR-desert method. II. Self-association and temperature-dependent glycosidic isomerization at pH 7. 22 55

A series of 4'-dehydrated derivatives of various dimeric Vinca alkaloids has been synthesized to further define the structure-activity relationships of Vinca alkaloids with onolytic potency. The concentrated sulfuric acid dehydration in most cases gave mixtures of the 3',4'-and two isomeric 4',20'-alkenes, which were isolated and characterized primarily by proton and 13C NMR. Compound tested for antitumor activity include the three dehydro isomers of 4'-deacetylvinblastine, 4-deacetylvincristine, and 4-deacetylvinblastine-23-amide and some4'-dehydrated derivatives epimeric at C-18'. Generally, the decrease in toxicity imparted by the new double bond was accompained by a decrease in potency. An exception was 3',4'-dehydro-4-deacetylvincristine, which showed a decrease in toxicity and increase in potency against at least one tumor in which vincristine itself has little effect.
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PMID:Alkaloids of Vinca rosea L. (Catharanthus roseus G. Don). 38. 4'-Dehydrated derivatives. 57 19

The synthesis of virtually all the lanthanide octaethylporphyrin complexes have been achieved by heating appropriate anhydrous lanthanide halide and octaethylporphyrin in imidazole melt at 210 degrees C for two hours. The lighter lanthanide porphyrin complexes are very susceptible to hydrolysis, the middle lanthanide porphyrin complexes are moderately stable, and the heavier lanthanide porphyrin complexes are relatively more stable to hydrolysis. Two out of four lanthanide porphyrin complexes studied in detail, namely ytterbium and lutetium octaethylporphyrins, aggregate in benzene and the Soret bands in their absorption spectra are about 6 nm shifted to higher energies upon a hundred-fold increase in their concentrations. The aggregations of these lanthanide porphyrin complexes in non-coordinating solvents have been further verified by 1H NMR spectral studies. This spectral behavior can be interpreted qualitatively in terms of the model of the molecular exciton interactions with stacking of at least two prophyrins. A dimeric structure of these lanthanide porphyrin complexes has been proposed on the basis of geometrical considerations. On the contrary, the europium and gadolinium octaethylporphyrins associate very weakly in benzene in the concentration range studied. All four lanthanide porphyrin complexes interact with pyridine and piperidine, and the Soret bands in their absorption spectra are about 8 nm shifted to low energies as compared with their values in pure benzene.
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PMID:Lanthanide octaethylprophyrins: preparation, association, and interaction with axial ligands. 62 34

13C nuclear magnetic resonance spectra have been obtained for a variety of high-spin iron(III) porphyrin compounds and corresponding mu-oxo-bridged dimeric species. Large hyperfine shifts and significant line broadening are observed. The monomeric complexes exhibit hyperfine shifts which are downfield with the exception of an upfield shift for the meso-carbon atom. Possible unpaired spin delocalization mechanisms and prospects for observing 13C NMR porphyrin resonances in high-spin ferrihemoproteins are discussed. Spectra reported here provide strategy for incorporation of 13C labels in hemoproteins either by biosynthetic or chemical means. The vinyl-CH2 resonances of iron(III) protoporphyrin IX located 260 parts per million downfield from tetramethylsilane are especially attractive from the standpoint of chemical labeling.
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PMID:Carbon-13 nuclear magnetic resonance spectroscopy of high-spin iron(III) porphyrin compounds. 68 61

After protection of cysteine-45 and -82 with iodoacetamide or N-ethylmaleimide, and in the presence of saturating concentrations of substrates, the supernatant isozyme of pig heart aspartate transaminase has been covalently modified at cysteine-390 with 3-bromo-1,1,1-trifluoropropanone. The modified enzyme retains 60-70% of the initial specific activity and is similar to native enzyme in pH and temperature stability. After tagging cysteine-390 with the fluorinated compound, the enzyme retains substrate and inhibitor binding abilities; as shown by direct spectrophotometric titration of the active-site chromophores. The 19F NMR spectrum of the modified enzyme has been obtained by a Fourier transform NMR method. Although the transaminase is a dimeric enzyme, 19F bound at each subunit's cysteine-390 gives rise to only a single 19F resonance upfield from that of trifluoroacetic acid. The fact that the chemical shifts of the 19F probe differ in native and guanidine hydrochloride (Gdn-HCl) denatured enzyme is interpreted as the effect of the native protein groups on the probe. The discordance between the changes induced by varying concentrations of Gdn-HCl on the 19F resonance parameters, on the one hand, and the changes in enzyme activity and prosthetic group absorbance, on the other, suggests that, in aspartate transaminase, cysteine-390 lies in an environment dissimilar from that of the active-site components.
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PMID:Sulphydryl group modification of aspartate aminotransferase with 3-bromo-1,1,1-trifluoropropanone during catalysis. 85 50

Molecular orientation of 5"-AMP in its stacked dimeric form in neutral aqueous solutions has been investigated at room temperature through the NMR-DESERT method proposed earlier by Akasaka et al. (J. Magn. Resonance, (1975) 18, 328-343). The effect of deuterium substitution of H8 of the adenine ring on the relaxation rate of H2 has become appreciable with increasing concentration of 5"-AMP, which should be attributed to the intermolecular H2-H8 interaction between adjacent adenine rings in the stacked dimer of 5"-AMP. The reciprocal sixth-power-averaged distance between H8 and H2 of the adjacent adenine rings in the stacked dimeric form obtained from the differential relaxation rate for H2 has been found to be almost constant (3.6 +/- 0.2 A S.D.) in the whole concentration range studied (0.1--1.0 M). The result has presented a direct proof of the existence of trans-stacking with a relatively large proportion (more than 60%) in the stacked dimeric form of 5"-AMP.
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PMID:Molecular orientation in the stacked dimer form of 5"AMP in aqueous solution. A study by the NMR-desert method. 85 71

The interaction of 3'-O-acetyldithymidilate (pdTpdT(Ac)), thymidine-3',5'-diphosphate (pdTp) and thymidine-3'-phenyl-phosphate-5'-phosphate (pdTpPh) with 2,4,6-triisopropylbenzene sulphonyl chloride (TPS) and N,N'-dicyclohexylcarbodiimide (DCC) in pyridine and dimethylformamide (DMF) was studied by pulsed NMR spectroscopy on phosphorus nuclei. Thymidine cyclic 3',5'-pyrophosphate and dimeric pyrophosphate derivatives were shown to be the main products of the reaction of pdTp with TPS and DCC. The former shows spin AB-system with the unusually large spin-spin coupling constant about 28Hz upfield to the signals of the dimeric pyrophosphates in NMR spectrum. Analogous spin AB-systems with large spin-spin coupling constants (up to 32 Hz) were observed in the spectra of the reaction mixtures of pdTpdT(Ac) with TPS or DCC and of pdTpPh with TPS. These spin AB-systems were ascribed to 3',5'-cyclic pyrophosphate derivatives of pdTpdT(Ac) and pdTpPh.
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PMID:Investigation of the mechanism of the synthesis of oligonucleotides. IX. 31P NMR spectra of the active dinucleotide derivatives and their analogs. 94 Jul 73

1H-NMR measurement and NMR susceptibility measurements were carried out with deuterohemin complexes in aqueous solution. The hydroxyaquo complex of deuterohemin, which is dimeric in weakly alkaline medium, turns into a low-spin dicyano complex on addition of cyanide. This reaction proceeds in two steps: whereas in the first, slow step a dimeric low-spin hydroxycyano complex is formed, in the second step the latter is converted quickly into the dimeric dicyano complex. The pK values for the overall reaction, the first and the second step were measured to be 23.25; 0.39 and 22.86, respectively. The values of free energy variation obtained therefrom suggest that conformational changes are decisive in the liganding of methemoglobin.
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PMID:[NMR spectroscopic characterization of deuterohemin complexes in aqueous media]. 118 13

Two modified forms of heparin, polymers A and B, have been prepared, one containing residues of nonsulfated alpha-L-idopyranosyluronic acid (3) and the other residues of alpha-L-galactopyranosyluronic acid (7), in place of the normal alpha-L-idopyranosyluronic acid 2-sulfate (1). In addition, both A and B contained 2-acetamido-2-deoxy-alpha-D-glucopyranosyl 6-sulfate residues (6) in place of the corresponding N-sulfated residues (2) of the original heparin. These polymers were subjected to sulfation under various conditions. Examination of the products by NMR spectroscopy showed that polymer A was sulfated initially at position-3 of residue 3, and that slower substitution occurred at position-3 of 6. By contrast, polymer B exhibited low regioselectivity, as sulfation occurred with about equal facility at positions-2 and -3 of 7, and -3 of 6. The sulfation products had no significant anti Xa activity. Based on the paramagnetic effects of Cu2+ and chemical shift displacements induced by Ca2+, NMR spectroscopy was used to compare cation-binding properties of A and B with those of heparin. In contrast to heparin, which forms a complex with Cu2+ detectable at a level of < 10(-3) mol per dimeric unit of the polymer, neither A nor B exhibited an interaction with the cation. However, polymer A was found to bind Ca2+, in this respect being distinct from the related modification, 1-->6, which contains a 2-sulfate group in 1, as well as from polymer B.
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PMID:Regioselectivity in the sulfation of some chemically-modified heparins, and observations on their cation-binding characteristics. 129 Oct 46

The designed peptide 1-methylimidazole-2-carboxamide netropsin (2-ImN) binds specifically to the sequence 5'-TGACT-3'. Direct evidence from NMR spectroscopy is presented that this synthetic ligand binds DNA as a 2:1 complex, which reveals that the structure is an antiparallel dimer in the minor groove of DNA. This is in contrast to the 1:1 complexes usually seen with most crescent-shaped minor groove binding molecules targeted toward A+T-rich tracts but reminiscent of a dimeric motif found for distamycin at high concentrations. These results suggest that sequence-dependent groove width may play an important role in allowing an expanded set of DNA binding motifs for synthetic peptides.
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PMID:Antiparallel side-by-side dimeric motif for sequence-specific recognition in the minor groove of DNA by the designed peptide 1-methylimidazole-2-carboxamide netropsin. 132 45


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