Specific, saturable, and high affinity binding of ¹²⁵I-low density lipoprotein to glass beads

¹²⁵I-Low density lipoprotein (¹²⁵I-LDL)^* binds tightly to glass beads at physiologic pH and ionic strength. This binding shows saturability, high affinity (half maximal binding achieved at 10-15 μg protein/ml), and specificity (unlabeled LDL but not HDL or albumin competes with ¹²⁵I-LDL for binding to the glass beads). In contrast to the binding of ¹²⁵I-LDL to the physiologic LDL receptor on the surface of human fibroblasts and lymphocytes, the binding of ¹²⁵I-LDL to bind to inert substances such as glass must be considered in the interpretation of studies in which ¹²⁵I-LDL binding to membrane receptors is measured. The data emphasize the importance of correlating observed ¹²⁵I-LDL binding with a physiologic action of the lipoprotein.