The Interaction of Apoprotein from Porcine High-Density Lipoprotein with Dimyristoyl Phosphatidylcholine. Electron Spin Resonance and Fluorescent Probe Studies

1 The interactions between the lipid and protein in complexes of dimyristoyl lecithin and porcine apoprotein were studied using electron spin resonance and fluorescent probes, dissolved in the lipid and covalently bonded to the protein. 2 The chain-melting transition of dimyristoyl lecithin is broadened on complexing with porcine apoprotein, indicating that the cooperative interaction between the lipid hydrocarbon chains is modified in the complex. 3 The broadening of the chain-melting transition is seen to be greatest by probes located at or near the glycerol region of the phospholipid. 4 Labels covalently bound to the protein experience only a small perturbation from the lipid chain-melting transition. 5 The results are interpreted as being consistent with a model for the complex, consisting of a lipid-bilayer, partially coated with protein and with some interdigitation of the protein.