Fig. 6. Degradation of endocytosed FGFRs. (A) Cell-surface proteins on HeLa cells, not transfected (NT) or transiently transfected with FGFR1, 2, 3 or 4 were biotinylated and the cells were then incubated for the indicated periods of time at 37°C in the presence of 100 ng/ml FGF1 and 20 U/ml heparin. After lysis, the solubilised receptor proteins were adsorbed to streptavidin-Sepharose and analysed by immunoblotting (IB) with appropriate anti-FGFR antibodies. (B) The intensity of the bands at time point zero was set to 100% and the relative amount of receptors at each time point was calculated. The presented values represent the average of three independent experiments. Error bars denote the s.d.