The effectiveness of various salts of the Hofmeister series as dissociating agents for human hemoglobin A tetramers has been investigated by light-scattering molecular-weight measurements. Dissociation of hemoglobin to half-molecules of alpha beta dimers follows the order of the series dictated predominantly by the sequence of the anions F- less than Cl- less than Br- less than ClO4- less than SCN-, I-, with the cations Na+ and K+ having relatively little effect on the observed dissociation. The use of equations derived for predicting the effects of dissociating reagents on the structure of subunit proteins [Herskovits, T. T., and Ibanez, V. S. (1976), Biochemistry 15, 5715] together with Setschenow constants based on the model amino acid data of Nandi and Robinson were found to give a satisfactory account of the dissociation behavior observed with many of the salts, giving reasonable estimates of the number of amino acids that form the smaller contact area of the alpha beta subunits of hemoglobin shown by the Perutz crystallographic model. The analysis of the dissociation data also extends the utility of the Setschenow constants tested for the characterization of the dissociation behavior of other subunit proteins.
The subunit dissociation of the hemocyanin of the lobster, Homarus americanus, by the various salts of the Hofmeister series and the hydrophobic reagents of the urea-guanidinium chloride (GdmCl) class was investigated by laser light scattering molecular weight measurements. The dissociations of the hemocyanin dodecamers to hexamers by the various salts and the lower members of the urea series are found to be rapid and reversible, as predicted by the mass action law for monomer-dimer type of reactions. The salts are found to be very effective dissociating reagents with the unusual order of increasing effectiveness, Cl- less than Br- less than I- less than ClO4-, SCN-. The ureas and GdmCl are found to be relatively ineffective dissociating agents. In addition, the ureas show a decreasing order of effectiveness in going from urea to methyl-, ethyl-, and propylurea. This suggests that hydrophobic interactions are not the dominant stabilizing forces between the pairs of hexamers that form the dodecameric structure. Polar and ionic interactions appear to be the major stabilizing forces of the dodecameric structure. The use of equations derived for predicting the effects of dissociating reagents and salts on the structure of subunit proteins [Herskovits, T. T., & Ibanez, V. S. (1976) Biochemistry 15, 5715-5721] together with binding and Setschenow constants based on model amino acid data is found to give good account of the dissociation behavior observed with the salts, urea, and methylurea in the presence of calcium ion at both pH 7.8 and pH 9.5. The apparent number of amino acids at the contact areas of the hexamers, Napp, required to fit the dissociation data were found to be 24 +/- 8 at pH 7.8 and 23 +/- 4 at pH 9.5. However, because of the possible effects of molecular microheterogeneity, the estimates of amino acids at the contact areas must be viewed with caution, depending on further investigations.
The HOME HF study demonstrates the feasibility of home BNP measurement and shows the potential value of fBNP as an index of emerging clinical deterioration. Assessment of the clinical value of this is required.
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