Specificity of isozymes of murine hepatic glutathione S-transferase for the conjugation of glutathione with L-phenylalanine mustard.
Glutathione S-transferase (GST) isozymes play a central role in the protection of cells from cytotoxic chemicals and have a putative role in the intrinsic and acquired resistance of tumors to cytotoxic drugs. We have isolated and purified GST isozymes from mouse liver (M. Warholm et al., Biochemistry, 25: 4119-4125, 1986) and analyzed the metabolic products of the reaction of L-phenylalanine mustard (L-PAM) with glutathione in the presence of GST isozymes, using reverse phase high performance liquid chromatography. At pH 6.5, the spontaneous conjugation of L-PAM and glutathione is suppressed and the major product at 60 min is the monochloro, monohydroxyl derivative of L-PAM. Addition of neither class mu nor class pi isozymes to the reaction has any effect on the metabolism of L-PAM. Only isozymes of the alpha GST class catalyze the conjugation of L-PAM with glutathione. In this case, the major metabolite at 1 h is the monochloro, monoglutathionyl conjugate. Increasing the amount of mu or pi isozyme in the reaction mixture has no effect on the metabolism of L-PAM, whereas increasing the amount of alpha isozyme completely supplants hydrolysis with conjugation. Thus, increased levels of class alpha GST isozyme may represent a specific mechanism whereby cells can acquire resistance to nitrogen mustards.
Bolton
M G
MG
Laboratory of Pharmacology and Experimental Therapeutics, Johns Hopkins Oncology Center, Baltimore, Maryland 21205.
Colvin
O M
OM
Hilton
J
J
D000818:Animals; D003600:Cytosol / Q000201:enzymology*; D005260:Female; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000502:physiology*; D008099:Liver / Q000201:enzymology*; D008297:Male; D008558:Melphalan / Q000378:metabolism*; D051379:Mice; D013379:Substrate Specificity
D007527:Isoenzymes; D005982:Glutathione Transferase; D005978:Glutathione; D008558:Melphalan