A comparison of the surface activities of rat plasma apolipoproteins C-II, C-III-0, C-III-3.

Rat apolipoproteins C-II, C-III-0 and C-III-3 give similar surface pressure (pi)-molecular area isotherms when spread at the air/water interface. When allowed to adsorb to the clean air/water interface, the intrinsic surface activity of apolipoprotein C-II is somewhat higher than that of apolipoprotein C-III. All three apolipoprotein C molecules can penetrate an egg phosphatidylcholine monolayer spread at the air/water interface causing an increase (delta pi) in surface pressure. Increasing the initial surface pressure (pi i) of the lipid monolayer decreases delta pi, and delta pi = 0 when pi i greater than or equal to 32 +/- 2 mN . m-1 for all three apolipoprotein C proteins. This implies that apolipoproteins C-II, C-III-0 and C-III-3 would adsorb and desorb similarly from the surfaces of lipoprotein particles during metabolism.