Size isomers of testosterone-estradiol-binding globulin exist in the plasma of individual men and women

Abstract We isolated testosterone-estradiol-binding globulin TeBG rapidly and in high yield from pooled pregnancy plasma. It showed two bands on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE). Both bands stained with three different monoclonal antibodies to TeBG, thus demonstrating their immunological similarity. Freshly drawn, individual sera, from men, women, and pregnant patients were submitted to microaffinity chromatography, a procedure which partially purifies TeBG in approximately 4 hr. The partially purified plasma was submitted to SDS PAGE, followed by immunoblotting. The blotted TeBG exhibited the same two bands seen in the isolated, purified protein. The size heterogeneity observed in TeBG purified from pooled pregnancy plasma therefore is a constituent property of TeBG. It is not secondary to: proteolysis occurring during isolation; a peculiarity of pregnancy plasma; or heterogeneity attendant upon the use of pooled plasma for isolation.