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KMID : 0614020020170010040
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Journal of Pharmaceutical Sciences (C.N.U.)
2002 Volume.17 No. 1 p.40 ~ p.45
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Oxidative Inactivation of Paraoxonase from Human Plasma
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Nguyen Duy-Su
Kim Ju-Ryung
Jeong Tae-Suk
Liu-Xi-Wen
Sok Dai-Eun
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Abstract
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Paraoxonase (PON), an enzyme associated with high density lipoprotein (HDL), is known to protect low density lipoprotein (LDL) from lipid peroxidation involving copper ion. However, PON activity was observed to decrease during LDL oxidation. Here, we attempted to elucidate the possible mechanism for the inactivation of PON. PON was partially purified from human plasma, and subjected to various oxidant systems. PON activity, based on the hydrolysis of phenyl acetate, decreased slightly after the exposure to H_2O_2 or ascorbate, while oxidants such as peroxynitrite or HOCl had no remarkable effect. Inclusion of Cu^2+ in the incubation with ascorbate (0.3∼1 mM) led to a rapid decrease of activity in a time-and concentration-dependent manner. In comparison, ascorbate/Cu^2+ system was much more effective than ascorbate/Fe^2+ system in inactivating PON. A further study indicates that general hydroxyl radical scavengers such as mannitol, ethanol or benzoate failed to prevent the PON inactivation. Based on these results, it is proposed that the PON inactivation during LDL oxidation may be ascribed mainly to the Cu^2+-catalyzed oxidation.
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KEYWORD
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Paraoxonase, lipoprotein, inactivation
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