Reversibility of the modification of Rhizopus delemar lipases by phosphatidylcholine

Rhizopus (Rh.) delemar (ATCC 34612) lipase is modified by its binding with phosphatidylcholine (PC); such binding enhances the lipoprotein lipase (LPL) activity, shifts the isoelectric point (pI) to the acidic side and decreases its alpha-helical content ((1980) J. Biochem. 88, 533-538). The results of density gradient ultracentrifugation proved that PC binding to lipase molecule was depleted by the treatment of PC-bound lipase with 0.3% Triton X-100 and 0.1 M NaCl. By this treatment, LPL activity was decreased almost to the original activity. At the same time, alpha-helical content recovered to that of the original lipase and the isoelectric point recovered from pI 6.5 to nearly the pI of the original lipase. These data indicate that the modification of Rh. lipase by PC is reversible. Furthermore, the results of an experiment with 2-[1(-14) C]oleoyl PC showed that lipase having high LPL activity contained about 5 mol of PC per mol of lipase.