Reversibility of the Modification of Rhizopus delemar Lipase by Phosphatidylcholine1

Abstract

Rhizopus (Rh.) delemar (ATCC 34612) lipase is modified by its binding with phosphatidylcholine (PC); such binding enhances the lipoprotein lipase (LPL) activity, shifts the isoclectric point (p I ) to the acidic side and decreases its α-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, α-helical content recovered to that of the original lipase and the isoelectric point recovered from p I 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-[I- ¹⁴ C]oleoyl PC showed that lipase having high LPL activity contained about 5 mol of PC per mol of lipase.