Reaction of Aflatoxin B1 Oxidation Products with Lysine
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- 作者：F. Peter Guengerich ; Kyle O. Arneson ; Kevin M. Williams ; Zhengwu Deng ; and Thomas M. Harris
- 刊名：Chemical Research in Toxicology
- 出版年：2002
- 出版时间：June 2002
- 年：2002
- 卷：15
- 期：6
- 页码：780 - 792
- 全文大小：195K
- 年卷期：v.15,no.6(June 2002)
- ISSN：1520-5010
文摘
Aflatoxin (AF) B1 exo-8,9-epoxide hydrolysis yields AFB1 dihydrodiol, which undergoes base-catalyzed rearrangement to, and is in equilibrium with, AFB1 dialdehyde. We investigatedthe reaction of AFB1 dialdehyde with albumin to generate a Lys adduct, previously characterizedby others [Sabbioni, G., Skipper, P. L., Büchi, G., and Tannenbaum, S. R. (1987) Carcinogenesis8, 819-824; Sabbioni, G. (1990) Chem.-Biol. Interact. 75, 1-15]. Pronase digestion of bovinealbumin serum treated with AFB1 dialdehyde and HPLC yielded the adduct, identified by itscharacteristic UV and mass spectra. The structure of the Lys-AFB1 dialdehyde adduct isconcluded to be (S)-
-amino-2,3-dihydro-2-oxo-4-(1,2,3,4-tetrahydro-7-hydroxy-9-methoxy-3,4-dioxocyclopenta[c][1]benzopyran-6-yl)-1H-pyrrole-1-hexanoic acid, structure B of the formerpaper and 8 of the latter, based on work with the methylamine adduct described in the followingpaper in this issue [Guengerich, F. P., Voehler, M., Williams, K. M., Deng, Z., and Harris, T.M. (2002) Chem. Res. Toxicol. 15, 793-798]. The time course of product formation at varyingconcentrations of AFB1 dialdehyde could be described by complexation with albumin with aKd of 1.5 mM and a first-order reaction rate with the N6-amino group of Lys of 0.033 min-1.The reaction of AFB1 dialdehyde with N2-acetylLys was monitored by UV spectroscopy andyielded a final spectrum similar to that of the described Lys adduct. Kinetic analysis of thechanges at pH 7.2 was best described with a scheme involving equilibrium of the dialdehydewith dihydrodiol and a rate-limiting reaction of AFB1 dialdehyde with the N6 atom of N2-acetylLys, with an apparent second-order rate constant of 2.6 × 103 M-1 min-1, followed byputative carbinolamine formation and rearrangement, collectively described by a first-orderrate constant of 7.6 min-1. Competition experiments with the hydrolysis of AFB1 exo-8,9-epoxideindicate that N2-acetylLys also reacts with the epoxide at pH 7.2 (k = 350 M-1 min-1) and 9.5(k = 1.8 × 103 M-1 min-1). This reaction might contribute to the formation of protein Lysadducts, depending upon the local concentration of free or protein Lys. Mass spectral analysisof trypsin digests of bovine serum albumin modified with AFB1 dialdehyde indicated selectivemodification of Lys455 and Lys548. Collectively, these results provide more insight into themechanism of formation of AFB1 dialdehyde-protein adducts and indicate that the formationof Lys adducts is a moderately efficient process. The binding of AFB1 dialdehyde to albuminor the protonation of the N6-amino group retards the reaction with Lys residues.
-amino-2,3-dihydro-2-oxo-4-(1,2,3,4-tetrahydro-7-hydroxy-9-methoxy-3,4-dioxocyclopenta[c][1]benzopyran-6-yl)-1H-pyrrole-1-hexanoic acid, structure B of the formerpaper and 8 of the latter, based on work with the methylamine adduct described in the followingpaper in this issue [Guengerich, F. P., Voehler, M., Williams, K. M., Deng, Z., and Harris, T.M. (2002) Chem. Res. Toxicol. 15, 793-798]. The time course of product formation at varyingconcentrations of AFB1 dialdehyde could be described by complexation with albumin with aKd of 1.5 mM and a first-order reaction rate with the N6-amino group of Lys of 0.033 min-1.The reaction of AFB1 dialdehyde with N2-acetylLys was monitored by UV spectroscopy andyielded a final spectrum similar to that of the described Lys adduct. Kinetic analysis of thechanges at pH 7.2 was best described with a scheme involving equilibrium of the dialdehydewith dihydrodiol and a rate-limiting reaction of AFB1 dialdehyde with the N6 atom of N2-acetylLys, with an apparent second-order rate constant of 2.6 × 103 M-1 min-1, followed byputative carbinolamine formation and rearrangement, collectively described by a first-orderrate constant of 7.6 min-1. Competition experiments with the hydrolysis of AFB1 exo-8,9-epoxideindicate that N2-acetylLys also reacts with the epoxide at pH 7.2 (k = 350 M-1 min-1) and 9.5(k = 1.8 × 103 M-1 min-1). This reaction might contribute to the formation of protein Lysadducts, depending upon the local concentration of free or protein Lys. Mass spectral analysisof trypsin digests of bovine serum albumin modified with AFB1 dialdehyde indicated selectivemodification of Lys455 and Lys548. Collectively, these results provide more insight into themechanism of formation of AFB1 dialdehyde-protein adducts and indicate that the formationof Lys adducts is a moderately efficient process. The binding of AFB1 dialdehyde to albuminor the protonation of the N6-amino group retards the reaction with Lys residues.