Figure 4.

(A) Binding and uptake, and (B) degradation of ¹²⁵I labelled low density lipoprotein (LDL) by cells stably transfected with the normal and mutant LDL receptor cDNAs. The cells were pre-incubated for 18 hours with medium containing lipoprotein deficient serum and sterols, then with ¹²⁵I labelled LDL for four hours. The results shown are the mean of triplicate incubations and represent saturable cell associated or degraded LDL, determined as the difference between cells incubated with ¹²⁵I labelled LDL in the presence or absence of an excess of unlabelled LDL. Non-specific cell associated or degraded LDL was always less than 5% of the total in cells expressing the normal LDL receptor cDNA. Similar results were obtained in two separate experiments with different preparations of LDL. Results are expressed as LDL protein/mg of cell protein, corrected for the amount of mature LDL receptor protein detected for each mg of cell protein by immunoblotting (relative to that in cells expressing the normal LDL receptor cDNA).