ISOLATION OF A MOUSE THETA-GLUTATHIONE-S-TRANSFERASE ACTIVE WITH METHYLENE-CHLORIDE

A glutathione S-transferase metabolizing methylene chloride has been i solated from mouse liver using a variety of chromatographic methods. N -terminal and internal amino acid sequences show that the enzyme, desi gnated GST T1-1, is closely related to the rat Theta-class GST 5-5. T he mouse enzyme, molecular mass 25 000 Da, has been isolated to homoge neity in active form with an approximate yield of 2% of the cytosolic activity towards methylene chloride. GST T1-1 has a specific activity of about 5.5 mu mol/min per mg of protein whereas the rat GST 5-5 is reported to have a specific activity of about 11 mu mol/min per mg of protein [Meyer, Coles, Pemble, Gilmore, Fraser and Ketterer (1991) Bio chem. J. 274, 409-414], demonstrating that both the rat and mouse enzy mes have similar activity with this substrate. Limited evidence was ob tained for a second enzyme, with a similar molecular mass (25 400 Da), which had an N-terminal sequence identical to that of rat GST 12-12. This protein, which was sequenced from a band on a gel, was extremely labile and could not be isolated to homogeneity. The partially purifie d enzyme was not active with methylene chloride.