Fe-superoxide dismutase and 2-hydroxy-1,4-benzoquinone reductase preclude the auto-oxidation step in 4-aminophenol metabolism by Burkholderia sp. strain AK-5

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.

Bacterial degradation of monocyclic aromatic amines

“…The next step, catalyzed by a 1,2,4-benzenetriol dioxygenase involves ring-cleavage of 1,2,4-benzenetriol to maleylacetic acid ( Figure 2B ). This bacterium expresses a Fe-containing superoxide dismutase and a 2-hydroxy-1,4-benzoquinone reductase that prevents the autoxidation of the labile intermediate 1,2,4-benzenetriol to 2-hydroxy-1,4-benzoquinone ( Takenaka et al, 2011 ).…”

Aspartic protease from Aspergillus (Eurotium) repens strain MK82 is involved in the hydrolysis and decolourisation of dried bonito (Katsuobushi)

“…7 The purified enzyme was partially digested using lysyl endopeptidase, and the peptides formed were fractionated as reported previously. 7 The limitedly hydrolysed peptides derived from myoglobin were separated by electrophoresis on e-PAGEL E-T15S gel (ATTO Corporation, Tokyo, Japan). The separated peptides in the gel were then electroblotted onto a PVDF membrane as described above.…”

Evolutive and structural characterization of Nostoc commune iron-superoxide dismutase that is fit for modification

“…The theory of free radicals and tumors holds that reactive oxygen species originating in redundant radicals attack organisms, leading to genetic mutations and tumors (Behrend et al, 2003;Li et al, 2008;Takenaka et al, 2011). SOD is supposed to be the main cellular superoxide anion-degrading enzyme that inhibits tumor growth (Zhang et al, 2002;Hu et al, 2005).…”