Kinetics and mechanism of apolipoprotein A-I interaction with L-alpha-dimyristoylphosphatidylcholine vesicles.

The dynamics of human apolipoprotein A-I (apo A-I) interaction with dimyristoylphosphatidylcholine (DMPC) vesicles were investigated in a 4000:1 DMPC/apo A-I (mol/mol) mixture where all the protein is bound to DMPC in stable vesicular complexes, and in a 100:1 DMPC/apo A-I (mol/mol) mixture which gives micellar complexes at equilibrium. Gel filtration and fluorescence methods (polarization and intensity) were used to follow the reaction kinetics. The binding of apo A-I to DMPC vesicles is a very rapid process which takes only a few minutes, while the formation of micellar complexes takes several hours at 25 degrees C and involves saturated complexes of apo A-I . DMPC and free apo A-I. The rate-limiting step in micellar complex formation is the breakdown of saturated vesicle . apo A-I complexes, a process that exhibits first order kinetics with a rate constant k = 0.22 h-1 and a half-life t 1/2 = 3 h 9 min.