Structural Units of Human 7s Gamma Globulin *

A number of observers in the past (1-3) have successfully degraded rabbit and horse antibodies with various enzymes, thus producing fragments retaining antibody activity. More recently Porter (4, 5) has produced split products of rabbit y-glob- ulin by treatment with papain and cysteine, two of which retained antibody activity as measured by their ability to inhibit precipitation of the original antiserum with homologous antigen, while the third appeared to retain the greatest antigenic specificity. Karush (6) and Nisonoff, Woernley and Wissler (7, 8) working with antihapten antibodies have clearly shown that these fragments are univalent. Putnam, Hsiao and Tan (9), employing similar techniques, have been able to split human y-globulin and myeloma proteins into two major chro- matographically separable fractions with sedimen- tation coefficients of approximately 3.5S. A preliminary report of some physical, chemical and immunological properties of similar subunits from human y-globulins and several human antibodies has been presented (10). In the present report, results are presented which indicate that following digestion of human y-globulin there are produced at least three fragments differing from each other in chemical properties. The major part of the antibody activity against three different antigens was found to be associated with one of these frag- ments, while smaller amounts were present in a second, antigenically similar fragment. The third fragment contained virtually no antibody activity but had additional antigenic specificity.