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 125-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 degrees 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.