Abstract
Behavior of apoA-I and apoC-II in aqueous solution was studied by using high performance liquid chromatography (HPLC), sedimentation equilibrium (SE) and circular dichroism (CD). ApoC-II is dominantly monomeric with rather randomized structure in solution. This has been indicated, by the monomeric molecular weight obtained by ultracentrifugal SE using Beckman Airfuge and Model E, by molecular seive type HPLC showing single peak at the position of larger molecular weight than its monomer, and by CD spectra with residual ellipticity at 222nm of 4600 deg. cm2/dmol that showed little change depending on the concentration of the protein.
ApoA-I, when its lyophilized specimen was solubilized in aqueous buffer, showed two peaks in HPLC with apparent molecular weights of tetra-and dimer. The first peak disappeared irreversibly with reciprocal increase of the second peak when the solution was heated. The kinetics of the disappearence of the first peak was the first order and the rate constant showed a straight line in Arrhenius plot, giving the activating energy=-120kcal/mol. The second peak could not be broken down any further by heating or by treating with chloroform: methanol, SDS, urea and DTT. SE resulted in compatible observation to the previous ones that apparent molecular weight increased from monomeric to origomeric as the concentration increased. CD study revealed its highly helical structure but the decrease in helicity as the first peak in HPLC disappeared and as the solution was diluted. Consequently, one must consider p rapid origomerization equilibrium of apoA-I in aqueous solution but there are another type of origomers which is the intermediate step in solubilizing apoA-I.
