FIGURE 4.

The AAA mutation hinders acid-dependent lipoprotein release, while the DRK mutation potentiates β-VLDL release in vitro. Release of prebound ¹²⁵I-LDL (A and C) or ¹²⁵I-β-VLDL (B and D) from fibroblasts expressing normal LDLR (WT), LDLR-AAA (AAA), or LDLR-DRK (DRK) was measured after 30 min at 4 °C (A and B) or 37°C(C and D) in medium buffered at pH 5.5, 6.0, 6.5, 7.0, or 7.5. In the 37 °C trials, 0.45 m sucrose was included in the medium to prevent clathrin-coated pit internalization. All experiments were performed in triplicate and are reported as the mean of the fraction of cell-associated lipoprotein remaining ± S.D.