Degradation of the subunits of receptor-bound human choriogonadotropin by Leydig tumor cells.

Biologically active, iodine-labeled derivatives of human choriogonadotropin in which all the iodine is localized either in the alpha or beta subunits have been prepared. It is found that upon binding to Leydig tumor cells these derivatives are ultimately degraded to 3'-monoiodotyrosine. A comparison of the rates of degradation of the derivatives labeled exclusively in the alpha or beta subunits show that the alpha subunit is degraded somewhat faster than the beta subunit. It was also found that NH4Cl, chloroquine and leupeptin inhibited the degradation of both subunits to the same extent. These results show that the Leydig tumor cells degrade both subunits of the receptor-bound human choriogonadotropin, and suggest that the two subunits are degraded by the same mechanism(s).