Metabolism of trans, trans-muconaldehyde, a cytotoxic metabolite of benzene, in mouse liver by alcohol dehydrogenase Adh1 and aldehyde reductase AKR1A4

Short, D.M. and Lyon, R.C. and Watson, D.G. and Barski, O.A. and McGarvie, G. and Ellis, E. (2006) Metabolism of trans, trans-muconaldehyde, a cytotoxic metabolite of benzene, in mouse liver by alcohol dehydrogenase Adh1 and aldehyde reductase AKR1A4. Toxicology and Applied Pharmacology, 210 (1-2). pp. 163-170. ISSN 0041-008X (http://dx.doi.org/10.1016/j.taap.2005.09.017)

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Abstract

The reductive metabolism of trans, trans-muconaldehyde, a cytotoxic metabolite of benzene, was studied in mouse liver. Using an HPLC-based stopped assay, the primary reduced metabolite was identified as 6-hydroxy-trans, trans-2,4-hexadienal (OH/CHO) and the secondary metabolite as 1,6-dihydroxy-trans, trans-2,4-hexadiene (OH/OH). The main enzymes responsible for the highest levels of reductase activity towards trans, trans-muconaldehyde were purified from mouse liver soluble fraction first by Q-sepharose chromatography followed by either blue or red dye affinity chromatography. In mouse liver, trans, trans-muconaldehyde is predominantly reduced by an NADH-dependent enzyme, which was identified as alcohol dehydrogenase (Adh1). Kinetic constants obtained for trans, trans-muconaldehyde with the native Adh1 enzyme showed a Vmax of 2141 ± 500 nmol/min/mg and a Km of 11 ± 4 μM. This enzyme was inhibited by pyrazole with a KI of 3.1 ± 0.57 μM. Other fractions were found to contain muconaldehyde reductase activity independent of Adh1, and one enzyme was identified as the NADPH-dependent aldehyde reductase AKR1A4. This showed a Vmax of 115 nmol/min/mg and a Km of 15 ± 2 μM and was not inhibited by pyrazole.

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