Ser11 plays several roles in the catalytic mechanism of rat glutathione transferase T2-2

Ser11 in rat glutathione transferase T2-2 promotes several steps in the cat alyzed reaction pathway of the enzyme. First, the residue lowers the pK(a) value of the enzyme-bound glutathione thiol by 2.2 pH units, from 7.9 to 5. 7. Secondly, the presence of Ser11 increases the reactivity of the enzyme-b ound glutathione thiolate, possibly by orienting the thiolate in a correct position for the reaction to take place. Thirdly, Ser11 increases k(on)(GSH ), or decreases k(off)(GSH). Fourthly, the dissociation rate constant for t he reaction product S-(1-menaphthyl)glutathione is increased by Ser11. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.