Conversion of melphalan to 4-(glutathionyl)phenylalanine. A novel mechanism for conjugation by glutathione-S-transferases.
One of the conjugates of melphalan, characterized following incubation with glutathione (GSH) and immobilized microsomal glutathione-S-transferases, has been identified as 4-(glutathionyl)-phenylalanine. This conjugate is formed by displacement of the mustard moiety. The structure was confirmed by reaction of the corresponding 4-halophenylalanines with GSH as well as by TLC, HPLC, and FAB mass spectrometry. Evidence is presented here to support the hypothesis that this novel reaction occurs via a cyclic aziridinium ion. To test this proposed mechanism, N,N-dimethyl-p-toluidine and its corresponding quaternary ammonium iodide salt were incubated with GSH in the presence of immobilized glutathione-S-transferases at 37 degrees C for 1 hr at pH 7.4. The tertiary amine did not react, whereas the quaternary compound produced 4-(glutathionyl)toluene. The effect of ring substituent requirements for the reaction was evaluated. The formation of GSH adducts of alkylating agents may be a factor in the development of resistance to these drugs.
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D005978:Glutathione / Q000031:analogs & derivatives* / Q000096:biosynthesis; D005982:Glutathione Transferase / Q000378:metabolism*; D066298:In Vitro Techniques; D008252:Macaca fascicularis; D008297:Male; D013058:Mass Spectrometry; D008558:Melphalan / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000096:biosynthesis
C052487:4-(glutathionyl)phenylalanine; D010649:Phenylalanine; D005982:Glutathione Transferase; D005978:Glutathione; D008558:Melphalan