Propylthiouracil. A substrate for the glutathione S-transferases that competes with glutathione.

TL;DRAbstract

In previous studies, we have observed that propylthiouracil (PTU) binds to Sephadex 6-100 eluates of rat liver cytosol associated with glutathione (GSH) Stransferase activity (EC 2.5.1.18). In order to study further this association between propylthiouracil and the GSH S-transferases, we examined the effect of propylthiouracil on the kinetics of the enzymatically catalyzed reaction between GSH and l-chloro-2,4-dinitrobenzene and found that propylthiouracil inhibited the reaction uncompetitively with respect to the latter reactant, but competitively with respect to the former (Ki = 0.62 mM). In addition to its activity as an inhibitor of the GSH S-transferases, propylthiouracil appeared to be a substrate. Reaction products between propylthiouracil and several of the lipophilic substrates for the transferases were identified and the enzymatically catalyzed formation of these products obeyed Michaelis-Menten kinetics. The specific activities of the partially purified GSH S-transferases AA

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