Activity-pH-inhibition interaction on purify $PON1 _{Q192} and PON1 _{R192}$

Human serum paraoxonase (PON1, EC 3.1.8.1.) is a high-density lipid (HDL)-associated, calcium-dependent enzyme; its physiological substrates are not known. PON1 exists in 2 major polymorphic forms: Q (glutamine) or R (arginine) at codon 192. PON1Q and R were separately purified by ammonium sulfate precipitation and hydrophobic interaction chromatography. The in vitro effects of some heavy metals (Hg, Cd, Cu, Co and Ni) has been previously investigated on the purified human serum PON1Q and R isoenzyme, using paraoxon as substrate at pH= 8 tris-base buffer. In this study, in vitro effects of some heavy metals (Hg, Cd, Cu, Co and Ni) were investigated on the purified human serum PON1Q and R isoenzyme, using paraoxon as substrate at pH= 10.5 tris-base buffer. Metals were more effective inhibitors on purified human serum $PON1 _{R192}$ activity than $PON1 _{Q192}$ activity also at pH=10.5 tris-base buffer. The $IC _{50}$ values of these metals exhibiting inhibition effects were found from graphs of paraoxsonase activity% by plotting the concentration of the metals.

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