Glutathione conjugation of aflatoxin B1 exo- and endo-epoxides by rat and human glutathione S-transferases.
Much evidence supports the view that the rate of conjugation of glutathione (GSH) with aflatoxin B1 (AFB1) exo-epoxide is an important factor in determining the species variation in risk to aflatoxins and that induction of GSH S-transferases can yield a significant protective effect. An assay has been developed in which the enzymatic formation of the conjugates of GSH and AFB1 exo-epoxide and the recently described AFB1 endo-epoxide is measured directly. 1H NMR spectra are reported for both the AFB1 exo- and endo-epoxide-GSH conjugates. Structural assignments were made by comparison with AFB1 exo- and endo-epoxide-ethanethiol conjugates, for which nuclear Overhauser effects were measured to establish relative configurations. The endo-epoxide was found to be a good substrate for GSH conjugate formation in rat liver cytosol while mouse liver cytosol conjugated the exo-epoxide almost exclusively. Human liver cytosol conjugated both epoxide isomers to much lower extents than did cytosols prepared from rats or mice. Purified rat GSH S-transferases catalyzed the formation of the AFB1 exo-epoxide-GSH conjugate in the order 1-1 approximately 4-4 approximately 3-3 greater than 2-2 greater than 4-6 (7-7 and 8-8 did not form the exo-epoxide-GSH conjugate at levels above the nonenzymatic rate). The only rat GSH S-transferases that conjugated the endo-epoxide were 4-4 and 4-6, with 4-4 being the more active.(ABSTRACT TRUNCATED AT 250 WORDS)
Raney
K D
KD
Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37232-0146.
Meyer
D J
DJ
Ketterer
B
B
Harris
T M
TM
Guengerich
F P
FP
D016604:Aflatoxin B1 / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism; D000818:Animals; D002384:Catalysis; D003600:Cytosol / Q000201:enzymology; D005978:Glutathione / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051379:Mice; D051381:Rats; D017207:Rats, Sprague-Dawley; D013237:Stereoisomerism; D013438:Sulfhydryl Compounds / Q000737:chemistry
D013438:Sulfhydryl Compounds; C006426:aflatoxin B1-2,3-oxide; D016604:Aflatoxin B1; D005982:Glutathione Transferase; D005978:Glutathione; C007638:ethanethiol