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  • 11
    Electronic Resource
    Electronic Resource
    Correlation of exchangeable (NH) and nonexchangeable (C2H) histidine resonances in the proton nmr spectrum of ribonuclease A in aqueous solution (1975)
    New York : Wiley-Blackwell
    Biopolymers 14 (1975), S. 975-986 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ionization characteristics of the hydrogen-bonded His 12 N1 proton observed to titrate between 11 to 13 ppm in the nmr spectrum of ribonuclease A in H2O solution are compared with the ionization characteristics of the four histidine C2 protons in the enzyme. Comparison of the pKa's of the enzyme in H2O and D2O in the absence and presence of cytidine monophosphate (-5′, -3′, and -2′) inhibitors, line widths in the presence of Cu II at pH 3.6 and 5.6, and chemical shifts in the presence of AgNO3 permit a correlation of the exchangeable His 12 N1 proton with the active site histidine C2 proton exhibiting the lower ionization pKa. The histidines with pKa of 5.1 and 5.6 in ribonuclease A in the absence of salt are assigned in this study to His 12 and His 119, respectively.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1975.360140507
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  • 12
    Electronic Resource
    Electronic Resource
    Assignment of the histidine 12-threonine 45 hydrogen-bonded proton in the nmr spectrum of ribonuclease A in H2O (1975)
    New York : Wiley-Blackwell
    Biopolymers 14 (1975), S. 959-974 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Described herein are proton nmr experiments on chemically modified derivatives of ribonuclease A designed to elucidate the origin of an exchangeable resonance, assigned previously to a histidine ring N proton that titrates between 11 to 13 ppm with a pKa of 6.1 in H2O solution. Histidines 48 and 105, which are distant from the active site, are eliminated as candidates for this resonance from inhibitor binding studies on the enzyme in acetate-water solutions. This exchangeable resonance titrates with modified pKa's and constant area over the above pH range in His-119-N1-carboxymethylated-RNase A and des-(121-124)-RNase A, thus eliminating the imidazole N3 proton in the His 119-Asp 121 hydrogen bond. In His-12-N1-carboxymethylated-RNase A, this resonance is also observable, but broadens on raising the pH above 7 and at elevated temperatures above neutrality. It exhibits a pH-independent chemical shift characteristic of the protonated state of histidine. On the basis of these findings, this exchangeable resonance, designated a, is assigned to the imidazole N1 proton of His 12, which is hydrogen-bonded to the carbonyl oxygen of Thr 45 in the crystal.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1975.360140506
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  • 13
    Electronic Resource
    Electronic Resource
    Reassignment of the active site histidines in ribonuclease A by selective deuteration studies (1975)
    New York : Wiley-Blackwell
    Biopolymers 14 (1975), S. 987-997 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The C2H resonance of the active site histidine residue designated AS-2, which has the lower pKa of the two active site histidines, has been correlated in both RNase A and RNase S by comparing the pH 3 to 5.5 regions of the chemical shift titration curves, the effect of the inhibitor CMP-3′ on the chemical shifts at pH 4.0, and the effect of Cu II on the line widths at pH 3.6. It has been demonstrated that resonance AS-2 is absent in the spectrum of RNase S′ reconstituted using S-peptide deuterated at the C2 of His 12, and in that of the RNase S′-CMP-3′ complex. We thus demonstrate that histidine AS-2 is in fact His 12 in both enzymes. This finding is in agreement with out previous assignment of the exchangeable NH proton in RNase A to His 12, but reverses the assignments of the active site histidine C2H resonances made earlier by other authors.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1975.360140508
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  • 14
    Electronic Resource
    Electronic Resource
    Biphasic helix-coil transition of the ethidium bromide·poly(dA-dT) and the propidium diiodide·poly(dA-dT) Complexes. Stabilization of base-pair regions centered about the intercalation site (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 857-873 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nonexchangeable base and sugar proton nmr resonances and the 260 and 278-nm uv-absorbance bands of the nucleic acid were utilized to monitor the temperature-dependent duplex-to-strand transition of the alternating purine-pyrimidine deoxyribopolynucleotide poly(dA-dT) in the absence and presence of ethidium bromide (EB) at phosphate/drug = 50, 28, and 15 and propidium diiodide (PI) at P/D = 50, 25, 15, 10, and 5 in 0.1 M salt between 50° and 100°C. The nmr and optical methods monitor a biphasic duplex-to strand transition for the drug-poly(dA-dT) complexes. We have monitored the dissociation of the drug from the complex at the ethidium bromide phenanthridine ring and side-chain proton nmr resonances and the propidium diiodide 494 and 535-nm uv-absorbance bands and demonstrate that dissociation of the drug corresponds to the higher temperature transition in the biphasic nucleic acid melting curves. The lower temperature cooperative transition is assigned to the opening of drug-free AT base-pair regions in the drug-poly(dA-dT) complex and exhibits an increase in transition midpoint and a decrease in cooperativity with increasing drug concentration. The higher temperature cooperative transition is assigned to the opening of AT base-pair regions centered about the bound drug in the complex and exhibits an increase in the transition midpoint on raising the drug concentration. The large upfield shifts of the phenanthridine ring (but not side chain) protons of ethidium bromide on complex formation demonstrate intercalation of the drug between base pairs of the poly(dA-dT) duplex. The nucleic acid base and sugar resonances of poly(dA-dT) in 0.1 M phosphate undergo chemical shift changes between 0° and 50°C indicative of premelting conformational transition(s).
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360160410
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  • 15
    Electronic Resource
    Electronic Resource
    Editorial: Molecular insights into the RNA world (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 97-100 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Mutagen-nucleic acid complexes at the polynucleotide duplex level in solution: Intercalation of proflavine into poly(dA-dT) and the melting transition of the complex (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 2739-2754 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nmr chemical shifts and line widths of the nucleic acid base and sugar proton resonances and the proflavine ring protons can be monitored through the melting transition of the proflavine + poly(dA-dT) complex, phosphate/dye (P/D) ratio = 24 and 8 in 1M salt solution. The nucleic acid and mutagen protons in the complex are in fast exchange between duplex and strand states with the midpoint of the melting transition monitored at the nucleic acid resonances increasing from 72.6°C for poly(dA-dT) to 78.1°C for the P/D = 24 complex and 83.4°C for the P/D = 8 complex in 1M salt solution. The melting transition monitored by the proflavine resonances were 80.0°C for the P/D = 24 complex and 84.3°C for the P/D = 8 complex in 1M salt solution. Since the nucleic acid is in excess at high P/D ratios, the nucleic acid transitions are an average for the opening of mutagen-free and mutagen-bound base-pair regions, while the proflavine transitions monitor the melting of mutagen-bound base-pair regions. The observed 0.75 to 0.95 ppm unfield shift at all four proflavine protons on formation of the complex with poly(dA-dT) provides direct evidence for intercalation of the mutagen between base pairs of the nucleic acid duplex. We have deduced the approximate overlap geometry between the proflavine ring and nearest-neighbor base pairs at the intercalation site from a comparison between experimental proflavine complexation shifts and those calculated for various stacking orientations. The experimental chemical shift of the poly(dA-dT) adenine H-2 resonance in the duplex state in the absence and presence of proflavine suggests that intercalation occurs preferentially at dT-dA sites. The selective chemical shift changes at the sugar H-2′,2″ and H-3′ resonances of the poly(dA-dT) duplex on complex formation demonstrates changes in the sugar pucker and/or torsion angles of the sugar phosphate backbone at the intercalation site.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360161212
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  • 17
    Electronic Resource
    Electronic Resource
    The structure of α-amanitin in dimethylsulfoxide solution (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1973-1986 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The backbone and side-chain conformations of the bicyclic octapeptide α-amanitin indimethylsulfoxide (DMSO) solution have ben deduced from analysis of the nmr spectrl parameters and conformational energy calculations. Several ambiguities in the nmr spectral assignments were resolved following a comparison with the recently published conformation of β-amanitin in the crystalline state. The peptide proton exchange and temperature coefficient data demonstrate strong intramolecular hyfrogen bonds for the GLY5 and Cys8 peptide protons. The vicinal proton coupling constants are consistent with the cyclic octapeptide udergoing chain reversl at the Ile6-Gly7 abd the Hyp2-Hyi3 dipeptide segments. The upfield shifts of the glycine and isoleucine protons demonstrate the folding of the indole ring of the Trp4-Cys8 brifge towards the Gly5-Ile6-Gly7 half of the Ile-amanitin molecule. The structure af α-amanitin in DMSO is defined by the (φψ) backbone rotation angles Trp4(-90, -60), Gly5 (+120, -120), Ile6(-6, +120), Gly7 (+45, +60), Cys8(-120, -60), Asn1 (+175, -175), Hyp2 (-160, -45), and Hyi3 (-90, -60). The study demonstrates that the structure of α-amanitin in solution is similar to the structure f β-amanitin in the crystalline state.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1978.360170812
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