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  • 1
    ISSN: 1573-4943
    Keywords: Lysozyme ; disulfide bond modification ; conformational analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A three-disulfide form of hen egg white lysozyme with Cys6 and Cys127 blocked by carboxymethyl groups was prepared, purified, and characterized for eventual use in protein folding experiments. Trypsin digestion followed by proline-specific endopeptidase digestion facilitated the unambiguous assignment of the disulfide bond pairings and the modified residues in this derivative. 3SS-lysozyme demonstrated nearly full enzymatic activity at itspH optimum,pH 5.5. The 3SS-lysozyme derivative and unmodified lysozyme were shown to be identical by CD spectroscopy atpH 3.6. Immunochemical binding assays demonstrated that the conformation of lysozyme was perturbed predominantly only locally by breaking and blocking the disulfide bond between Cys6 and Cys127. Both 3SS-lysozyme and unmodified lysozyme exhibited reversible thermally induced transitions atpH 2.0 but theT m of 3SS-lysozyme, 18.9°C, was found to be 34° lower than that of native lysozyme under the same conditions. The conformational chemical potential of the denatured form of unmodified lysozyme was determined from the transition curves to be approximately 6.7 kcal/mol higher than that of the denatured form of 3SS-lysozyme, atpH 2.0 and 35°C, if the conformational chemical potential for the folded forms ofboth 3SS-lysozyme and unmodified lysozyme is arbitrarily assumed to be 0.0 kcal/mol. A calculation of the increase in the theoretical loop entropy of denatured 3SS-lysozyme resulting from the cleavage of the Cys6-Cys127 disulfide bond, however, yielded a value of only 5.4 kcal/mol for the difference in conformational chemical potential. This suggests that, in addition to the entropic component, there is also an enthalpic contribution to the difference in the conformational chemical potential corresponding to approximately 1.3 kcal/mol. Thus, it is concluded that the reduction and blocking of the disulfide bond between Cys6 and Cys127 destabilizes 3SS-lysozyme relative to unmodified lysozyme predominantly by stabilizing the denatured conformation by increasing its chain entropy.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4943
    Keywords: Fibrinogen peptides ; competitive radioimmunoassay ; immunochemical affinity constants ; conformational analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Published results on the immunochemical reactivities of fibrinogen and fibrinogen fragments with fibrinogen-elicited antibodies that had been fractionated on the basis of preferential interaction with Aα [Nagy, J. A., Meinwald, Y. C., and Scheraga, H. A. (1982),Biochemistry 21, 1794–1806] and Bβ [Nagy, J. A., Meinwald, Y. C., and Scheraga, H. A. (1985)Biochemistry 24, 882–887] peptides of this bivalent antigen have been reinterpreted. First, the multivalent counterpart of the Scatchard analysis has been used to determine the intrinsic association constant for the interaction of antibody with [125I]fibrinogen, the radiolabeled ligand used in subsequent competitive binding studies. Second, the corresponding affinity constant for native fibrinogen has been evaluated from the relevant competitive radioimmunoassays by means of a quantitative analysis that takes into account the bivalency of both the radiolabeled and native fibrinogen molecules. Finally, affinity constants for the interactions of various fibrinogen fragments with antibody are also obtained by the procedure, and their magnitudes rationalized in terms of the equilibrium coexistence of unreactive (disordered) and native (functional) states of the fibrinogen peptides.
    Type of Medium: Electronic Resource
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