Enzymolysis of high density lipoprotein with a combination of membrane-immobilized esterase and trypsin

Apolipoprotein A-1 (apo A-1), a major component of high density lipoprotein (HDL), was efficiently digested by membrane-immobilized trypsin after HDL was treated with membrane-immobilized esterase. Compared to treatment with membrane-immobilized trypsin alone, the relative amounts of apo A-1 polypeptides, m/z 1723.78 and m/z 1568.82, increased by 2.7- and 3.9-fold, respectively, when HDL was treated with membrane-immobilized esterase and trypsin. Furthermore, the efficient digestion of apo A-1 by trypsin was inhibited when HDL was treated with membrane-immobilized esterase in the presence of an esterase inhibitor, 6,9-diamino-2-ethoxyacridine (acrinol). The data indicate that the lipid components of lipoproteins are released by membrane-immobilized esterase. This method can be used to investigate the structure and function of other apolipoproteins.