Fe-superoxide dismutase and 2-hydroxy-1,4-benzoquinone reductase preclude the auto-oxidation step in 4-aminophenol metabolism by <Emphasis Type="Italic">Burkholderia</Emphasis> sp. strain AK-5 |
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Authors: | Shinji Takenaka Jyun Koshiya Susumu Okugawa Akiko Takata Shuichiro Murakami Kenji Aoki |
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Institution: | (1) Department of Applied Biological Chemistry, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan;(2) Department of Bioscience, Biotechnology and Agrochemistry, Faculty of Agriculture, Meiji University, Tama-ku, Kawasaki 214-8571, Japan;(3) Department of Nutritional Management, Faculty of Nutritional Science, Sagami Women’s University, Bunkyo, Sagamihara 228-8533, Japan |
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Abstract: | Burkholderia sp. strain AK-5 converts 4-aminophenol to maleylacetic acid via 1,2,4-trihydroxybenzene, which is unstable in vitro and non-enzymatically
auto-oxidized to 2-hydroxy-1,4-benzoquinone. Crude extract of strain AK-5 retarded the auto-oxidation and reduced the substrate
analogue, 2,6-dimethoxy-1,4-benzoquinone, in the presence of NADH. The two enzymes responsible were purified to homogeneity.
The deduced amino acid sequence of the enzyme that inhibited the auto-oxidation showed a high level of identity to sequences
of iron-containing superoxide dismutases (Fe-SODs) and contained a conserved metal-ion-binding site; the purified enzyme showed
superoxide dismutase activity and contained 1 mol of Fe per mol of enzyme, identifying it as Fe-SOD. Among three type SODs
tested, Fe-SOD purified here inhibited the auto-oxidation most efficiently. The other purified enzyme showed a broad substrate
specificity toward benzoquinones, including 2-hydroxy-1,4-benzoquinone, converting them to the corresponding 1,4-benzenediols;
the enzyme was identified as 2-hydroxy-1,4-benzoquinone reductase. The deduced amino acid sequence did not show a high level
of identity to that of benzoquinone reductases from bacteria and fungi that degrade chlorinated phenols or nitrophenols. The
indirect role of Fe-SOD in 1,2,4-trihydroxybenzene metabolism is probably to scavenge and detoxify reactive species that promote
the auto-oxidation of 1,2,4-trihydroxybenzene in vivo. The direct role of benzoquinone reductase would be to convert the auto-oxidation
product back to 1,2,4-trihydroxybenzene. These two enzymes together with 1,2,4-trihydroxybenzene 1,2-dioxygenase convert 1,2,4-trihydroxybenzene
to maleylacetic acid. |
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