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  • Title: Lipoprotein lipase catalyzed hydrolysis of water-soluble p-nitrophenyl esters. Inhibition by apolipoprotein C-II.
    Author: Quinn DM, Shirai K, Jackson RL, Harmony JA.
    Journal: Biochemistry; 1982 Dec 21; 21(26):6872-9. PubMed ID: 7159570.
    Abstract:
    Bovine milk lipoprotein lipase (LpL) catalyzes the hydrolysis of the water-soluble esters p-nitrophenyl acetate (PNPA) and p-nitrophenyl butyrate (PNPB). The same protein and same active site are involved in hydrolysis of water-soluble p-nitrophenyl esters and emulsified trioleoylglycerol since (a) trioleoylglycerol hydrolysis and PNPB hydrolysis activities coelute from the heparin-Sepharose affinity column used to purify LpL and (b) LpL-catalyzed hydrolyses of trioleoylglycerol and PNPB are inhibited to equal extents by phenylmethanesulfonyl fluoride. The effect of apolipoprotein C-II (apoC-II) on the LpL-catalyzed hydrolysis of PNPA and PNPB has been determined. ApoC-II inhibits hydrolysis of both esters, with a maximum extent of inhibition of 70-90%. Inhibition of the LpL-catalyzed hydrolysis of PNPB is specific for apoC-II, since apolipoproteins A-I, C-I, and C-III-2 have little effect on this reaction, and is partial noncompetitive in form. KI values for apoC-II inhibition of the LpL-catalyzed hydrolysis of PNPA and PNPB are in the range 0.26-0.83 microM. The effect of apoC-II on the temperature dependences of LpL-catalyzed hydrolysis of both esters and on NaCl inhibition of LpL-catalyzed PNPB hydrolysis is consistent with a change in rate-determining step with LpL and apoC-II interact. These results indicate not only that there is an interaction between apoC-II and LpL in aqueous solution in the absence of a lipid interface but also that this interaction conformationally modulates the active site of the enzyme.
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