Kinetic study of the interaction of glutathione with four antitumor disulfides: possible mechanism for cellular glutathione depletion.
The reactions between the cellular tripeptide, glutathione (GSH) and four disulfide derivatives of 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG) (compounds 1-4) were studied kinetically. The decyl and phenyl derivatives of 6-MP and 6-TG were reacted with GSH in phosphate buffer (pH 7.4 or 6.0) at 25.0 degrees C and were monitored spectrophotometrically by observing the release of 6-MP and 6-TG. Second order kinetics were observed, with rate constants of 142, 564, 4174 and 429 M-1 s-1 being measured for compounds 1-4, respectively. When the reactions were carried out in the presence of GSH-S-transferase the rates were enhanced 1.3-5.4 times those observed in the absence of enzyme. Products of the reactions were isolated by chromatography and tentatively identified by TLC or fast atom bombardment mass spectrometry. It was observed that GSH reacted with each disulfide in a 1:1 manner, forming a mixed disulfide between GSH and decanethiol or thiophenol while releasing 6-MP or 6-TG. It was concluded that the reported depletion of GSH from EMT6 cells after exposure to these disulfides could be due to their reaction with GSH, and the formation of the mixed disulfides.
Kirkpatrick
D L
DL
Department of Chemistry, University of Regina, Saskatchewan, Canada.
D000970:Antineoplastic Agents; D004220:Disulfides; D005978:Glutathione / Q000031:analogs & derivatives / Q000378:metabolism; D019803:Glutathione Disulfide; D007700:Kinetics; D015122:Mercaptopurine / Q000031:analogs & derivatives*; D013056:Spectrophotometry, Ultraviolet; D013866:Thioguanine / Q000031:analogs & derivatives*
D000970:Antineoplastic Agents; D004220:Disulfides; D015122:Mercaptopurine; D013866:Thioguanine; D005978:Glutathione; D019803:Glutathione Disulfide