Binding of ethacrynic acid to hepatic glutathione S-transferases in vivo in the rat

Ethacrynic acid is a substrate for rat glutathione $\text{S}$-transferases $\text{in}$$\text{vitro}$ (1,2). In their study defining the importance of the glutathione $\text{S}$-transferases in the hepatic metabolism and biliary excretion of ethacrynic acid, Wallin $\text{et}$$\text{al}$. (3) suggested that a small but consistent portion of the administered drug was bound selectively and covalently to the transferases. Such an association would represent a unique example of covalent binding of a drug to the metabolizing enzyme without prior microsomal enzyme activation. We have undertaken these studies, therefore, to characterize the binding of ethacrynic acid to the glutathione $\text{S}$-transferases and to delineate the selectivity of this binding.