Sedimentation analysis of a multiple myeloma gamma-G-globulin and one of its mercaptoethylamine reaction products.

Descriptions of some thermodynamic properties and transport behavior in solution of an intact multiple myeloma yG-globulin and of one of the products of its reaction with mercaptoethylamine have been provided. For the sedimentation equilibrium experiments, the parent yG-globulin was dissolved in three solvent systems: cacodylate buffer, its 8 M urea solution and its 6 M guanidine hydrochloride solution, all at pH 7. Molecular weight and second virial coefficient data were also obtained for the mercaptoethylamine reaction product in 6 M urea solvent. Sedimentation velocity experiments were performed with the same solutions. The concentration dependence, both of apparent molecular weight and of sedimentation coefficient, for the parent molecule in 6 Y guanidine hydrochloride is quite normal. The same may be said of the corresponding behavior of the submolecule in 6 M urea buffer solution. On the other hand, suitable interpretations of sedimentation equilibrium and sedimentation transport data for the solutions of the yG-globulin in cacodylate and 8 M urea buffers seem to require the use of an association mechanism. A simplified theory, based on the assumption that only dimerization occurs in solution, is presented which makes use of a combination of the two kinds of information. In this way, it has become possible to provide a value for the dimerization constant and to assign limiting sedimentation coefficients for monomer and dimer. For the reasons given, the dimerization is believed to take place in an end-to-end fashion.