Antigenic structure of human gonadotropins: importance of protein moiety to the antigenic structure of human chorionic gonadotropin.

Abstract

An apparently homogeneous preparation of HCG with a potency of 12,800 IU/mg was prepared from a urinary material containing 3000 IU/mg, and its amino acid and carbohydrate composition was determined. The antigenic structure of this preparation was analyzed with rabbit antiserum to crude HCG by microcomplement fixation. None of the carbohydrate components of HCG inhibited CF reactions in this immune system. Treatment of HCG with neuraminidase, β-glucosidase or neuraminidase plus β-glucosidase did not affect the complementfixing activity of the hormone. However, biologic activity of the hormone was markedly reduced by treatment with neuraminidase. Limited tryptic hydrolysis of HCG caused a decrease in both biologic and complement-fixing activities. Subjection to either elevated temperatures of 60 and 100 C or 7m urea of HCG resulted in variable degrees of inactivation of both biologic and complement- fixing activities. When urea was removed by dialysis, partial regeneration of these 2 activities occurred. These data suggest that the carbohydrate moiety of HCG molecule is essential for the biologic activity but is not involved in the antigenic structure, that the protein moiety is important for these 2 activities and that the 2 activities require an ordered conformation of the protein moiety. (Endocrinology86: 97, 1970)