The pentaammineruthenium(III)histidine complex in ribonuclease A: application to the assignment of histidine proton resonances.
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Chemical Phenomena↗
Biomedical subjects
C R Matthews
Publications and source records attributed to C R Matthews.
The pentaammineruthenium(III)-histidine complex in ribonuclease A as an optical probe of conformational change.
The formation of stable transition metal complexes between pentaammineruthenium(III) and the imidazole moiety of histidine residues in ribonuclease A is described. Studies of the kinetics of incorporation suggest that three of the four histidines are reactive and ion-exchange chromatography affords the isolation of three derivatives containing a single ruthenium-histidine complex. Equilibrium studies of the thermal- and urea-induced unfolding of one of these derivatives show that the ligand-to-metal change-transfer absorptions above 300 nm can be used to follow the conformational changes in the vicinity of the complex. For the urea-induced unfolding of this derivative, the coincidence of the transition curves obtained from the change-transfer absorptions and from difference ultraviolet spectroscopy at 286 nm, which measures the exposure of buried tyrosine residues to solvent, suggest that only two conformations, native and unfolded, are present at equilibrium in significant concentrations.
Animals↗
Effect of single amino acid substitutions on the thermal stability of the alpha subunit of tryptophan synthase.
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Amino Acids↗
Mutagenic and toxic effects of ruthenium.
Selected platinum and ruthenium complexes were tested for their ability to cause Salmonella typhimurium strains TA98 and TA100 to revert to histidine independence. The results indicate that ruthenium compounds are capable of reverting both strains while cis-Cl2(NH3)2Pt primarily causes reversions in strain TA100. In addition, cis-platinum is an order of magnitude more mutagenic and toxic than are the ruthenium complexes. Selected compounds were also tested for their ability to induce the bacterial SOS system in the Bacillus subtilis Comptest. In this system, cis-platinum similarly showed greater inducing ability than did the ruthenium complexes. These results also demonstrated that the nature of the sixth ligand in the ruthenium compounds has a significant effect on the mutagenic capacity of these agents.
Bacillus subtilis↗
Aminoacyl-transfer RNA populations in mammalian cells chromatographic profiles and patterns of codon recognition.
The chromatographic profiles of 20 aminoacyl-tRNAs from rabbit liver were compared to those of rabbit reticulocytes by reverse phase chromatography and the chromatographic profiles of 20-aminoacyl-tRNAs from bovine liver were compared to those of bovine brain. The two rabbit tissues showed significant differences in the elution profiles of most aminoacyl-tRNAs, while the elution profiles of the aminoacyl-tRNAs from the bovine tissues showed fewer differences. The patterns of codon recognition of several aminoacyl-tRNAs fractionated from rabbit reticulocytes have also been compared to those fractionated from rabbit liver.
Amino Acyl-tRNA Synthetases↗
Nuclear magnetic resonance studies of residual structure in thermally unfolded ribonuclease A.
A proton nuclear magnetic resonance study of the four histidine residues of thermally unfolded ribonuclease A has provided evidence that two of the residues are in regions of residual structure, whereas the other two are freely exposed to solvent. Histidine-48 and, tentatively, histidine-105 occupy an environment at 69 degrees characterized by residual structure and display a pK value of 5.75 and a spin-lattice relaxation time of about 0.8 sec at pH 5.5. Histidine-12 and, tentatively, histidine-119 are in an environment at 69 degrees which is freely accessible to solvent and show a pK value of 5.96 and a spin-lattice relaxation time of about 1.1 sec at pH 5.5.
Computers↗
Nuclear magnetic resonance titration curves of histidine ring protons. The effect of temperature on ribonuclease A.
The ionization constants of 3 of the histidine residues of ribonuclease A have beenobtained at 5 temperatures from the nuclear magnetic resonance titration curves of the imidazole C2 proton resonances. Thermodynamic parameters derived from the ionization constants indicate that histidine residues 105 and 119 are fairly well exposed to solvent, while histidine residue 12 is in a somewhat more restricted environment. Measurements of the low pH inflection present in the titration curve of histidine-12 yield a large negative entropy value, indicating that the group givine rise to this inflection is also buried.
Calorimetry↗
A Fourier transform NMR study of the thermal denaturation of ribonuclease A at low pH.
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Animals↗
Nuclear magnetic resonance study of the thermal denaturation of ribonuclease A: implications for multistate behavior at low pH.
The thermal denaturation of ribonuclease A has been studied by use of Fourier transform nuclear magnetic resonance by monitoring the imidazole C-2 proton resonances of the histidine residues as a function of temperature at pH 1.3. As the temperature is raised, a slow chemical exchange process results in the disappearance of the peaks corresponding to the native conformation and the appearance of a single peak corresponding to histidine in the denatured state. The disappearance of the native peaks is not simultaneous, implying that at least two regions of the molecule denature at different temperatures. Also, fast chemical exchange processes result in small chemical shifts that appear to be related to local conformational changes. The observed phenomena have been shown to be reversible by the measurement of absorbance at 278 nm, enzyme activity, and nuclear magnetic resonance spectroscopy. The results of this equilibrium study support a multistate denaturation mechanism for ribonuclease A at pH 1.3.
Amino Acid Sequence↗