to study endocytosis in the absence of ligand binding , the cell surface was labeled at 4 degrees c with the 125i-iodinated impermeant reagent sulfosuccinimidyl-3- ( 4-hydroxyphenyl ) propionate , the cells were incubated at 37 degrees c for different times and the amount of internalized receptor was determined by protease digestion of surface proteins and immunoprecipitation .
C0699040
cell surface
C0007634
cells