Binding characteristics of high density lipoprotein subclasses to porcine liver, adrenal and skeletal muscle plasma membranes

Abstract 1. 1. We compared binding characteristics of 125 I-labeled high density lipoprotein (HDL) subclasses to porcine liver, adrenal and skeletal muscle plasma membranes. 2. 2. HDL subclasses were discriminated by their buoyant densities (HDL 2 and HDL 3 ) or by their apolipoprotein (apo) content (Lp-AI (particles containing apoA-I but no apoA-II) and LpA-I/A-II (particles containing both apoA-I and apoA-II)). 3. 3. HDL 2 and HDL 3 showed saturable binding to the three types of membrane preparations. 4. 4. No differences were found in the K d s within one HDL subclass. 5. 5. K d s and maximal binding of HDL 2 were lower than these of HDL 3 . Unlabeled HDL 2 and HDL 3 , but not LDL, effectively displaced 125 I-HDL 2 and 125 I-HDL 3 . 6. 6. Binding of HDL was independent of the concentration of Nad and did not require calcium. 7. 7. These results suggest a process mediated by a single specific receptor in porcine liver, adrenal and skeletal muscle plasma membranes. 8. 8. We also studied binding characteristics of HDL subclasses Lp-AI and LpA-I/A-II to porcine liver membranes. LpA-I showed the highest K d and maximal binding. 9. 9. All types of HDL subclasses studied (i.e. HDL 2 , HDL 3 , LpA-I and LpA-I/A-II) effectively competed for binding of both Lp-AI and LpA-I/A-II, suggesting that the HDL subclasses studied bind to the same receptor by their apoA-I moiety.