HEPATIC-UPTAKE OF DESIALYLATED TESTOSTERONE-OESTRADIOL-BINDING GLOBULIN IN THE RAT

Testosterone-oestradiol-binding globulin (TeBG) isolated from bovine serum was desialylated by treatment with neuraminidase and its properties were compared with intact TeBG. No significant differences were observed in the testosterone-binding capacity or antigenic determinant, but electrophoretic mobility of asialo-TeBG decreased slightly. When injected into rat vein, 125I-labelled asialo-TeBG was rapidly taken up by the liver, whereas 125I-labelled intact TeBG remained in the circulation for a much longer period. Galactose oxidase treatment of asialo-TeBG, which presumably oxidized the primary alcohol of galactose at C-6 to an aldehyde, caused a reversion of its survival time in the blood to that of intact TeBG. When incubated with isolated rat liver cells at 20°C, the desialylated, but not intact, TeBG was rapidly taken up, and its uptake was inhibited by excess amount of asialo-orosomucoid. Under these conditions in vitro, [3H]testosterone bound to asialo-TeBG was taken up by the liver cells together with the asialo-TeBG.