[Isolation of a gamma heavy chain fragment from normal human serum]

Several components of catodic electrophoretic migration in serum and urine are present in normal individuals and in rabbit serum. There also exists in man and in some animals, serum fractions of low molecular weight. These types of serum components may be or may not be related with the IgG. In a previous study we have isolated two components in the slow catodic electrophoretic area of the normal human serum (NHS). One of them was identified as an IgG subclass and the other component presented a clear line of precipitation to gamma heavy chain specific immuno-serum. This latter component was found in the post gamma-globulin area crossing the IgG arc in the I.E. analysis. Its molecular weight was variable from 3700 to 9500. In this paper a differential analysis of the gamma fragment isolated for us, is made and its relationship with Fc subfragments of pepsin-digested IgG is studied. In order to obtain this comparative study, the electrophoresis, gel diffusion immunoelectrophoresis gel chromatography and analytic ultracentrifugation techniques are employed. The post-gammaglobulin fraction has been isolated from total normal human serum without previous manipulation, or with the gammaglobulin fraction precipitated with saturated ammonium sulphate, in Sephadex G-200 chromatography. These two fractions present similar immunelectrophoretical characteristics. The constant sedimentation is 0.90 S and the approximated molecular weight is 7000. Since the pepsin digestion of IgG produced Fc subfragments of low molecular weight, we have isolated and submitted this immunoglobulin to peptic digestion. The G-75 Sephadex filtration shows an isolated post-gamma-globulin of I.E. sedimentation constant and molecular weight whose characteristics are similar to the isolated serum post-gammaglobulin fraction. The antigenical analysis in I.D. shows a total identity between the pepsin digested post-gammaglobulin and the fragment obtained for us from the human serum to an anti-heavy gamma chain immuno-serum and to a rabbit serum anti-fraction produced for us. These events suggest that this isolation post-gamma-globulin fraction corresponds to a Fc subfragment of the IgG.