Studies on the Conformation of Purified Human and Canine γA-Globulins and Equine γT-Globulin by Optical Rotatory Dispersion

Abstract

Abstract The isolation of immunochemically pure samples of γA myeloma proteins from human and canine sera and of equine γT-globulin antibodies and a γT paraprotein is described. Antigenic and ultracentrifugal analyses of the isolated proteins also are presented. The optical rotatory dispersion curves of the γA- and γT-globulins show minima near 230 and 225 mµ and maxima near 206 mµ. The Cotton effect at 240 mµ characteristic of human and equine γG-globulins could not be detected in either intact γA- or γT-globulins. A rare human γA2 subclass myeloma protein is not distinguishable from γA1-globulins by rotatory dispersion despite considerable differences in structure. Conversion of the dimeric canine γA-globulin to the monomer on mild reduction is not accompanied by any detectable change in conformation. The optical rotatory dispersion curves of F(ab')2 fragments produced by peptic digestion of human γA- and equine γT-globulins show single minima near 225 mµ. The F(ab')2 fragment of γA-globulin shows a Cotton effect at 240 mµ, whereas that of γT-globulin does not. In both fragments the levorotation above 235 mµ is considerably lower than in the parent protein. The results indicate that conformational differences exist between both human γA- and equine γT-globulins and their respective γG-globulins. While the rotatory dispersion spectra of the γA- and γT-globulins show over-all similarities, comparison of their respective peptic fragments suggests that there is some difference in conformation.