Interaction of ebselen with glutathione S-transferase and papain in vitro

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The interaction of ebselen(2-phenyl-1,2-benzisoselenazol-3(2 H)-one) with rat liver cytosolic glutathione S-transferases (GSTs) and the plant cysteine protease, papain, was studied as cysteine residues are important for the activity of these enzymes. The capacity of GST 1–2 and 3–4 for ebselen binding is similar (1.5 mol ebeselen/mol GST isozyme), while GST 2-2 and GST 7-7 bind 0.3 and more than 2.0 mol ebselen/mol GST isozyme, respectively. Ebselen does not bind to N-ethylmaleimide-treated GST, and its binding to GST is prevented by 5mM thiol. Ebselen irreversibly inactivates the different GST isozymes with a second order rate constant ranging from 20 to 2250 M −1 sec −1 for the different subunits. GST inhibition by ebselen is partially restored by 5 mM thiols. Ebselen binds to untreated papain and to cysteine-treated papain at a ratio of about 0.1 and 0.75 mol ebselen/mol papain, respectively. Ebselen does not bind to N-ethymaleimide-treated papain, and its binding to papain is interfered with by added thiols. Papain is inactivated by ebselen with a second order rate constant of 1800 M −1 sec −1 in the absence of thiols. However, in the presence of GSH, 2-mercaptoethanol orsodium borohydrine, ebselen exerts an activating effect on papain. The binding of ebselen by a seleno-sulfide bond to cysteine residues of GSTs and papain leads to their inactivation.