Reaction: (1a) 2 2-aminophenol + O2 = 2 6-iminocyclohexa-2,4-dienone + 2 H2O
(1b) 2 6-iminocyclohexa-2,4-dienone + oxidant = 2-aminophenoxazin-3-one + reduced oxidant (spontaneous)
For diagram click here.
Glossary: 6-iminocyclohexa-2,4-dienone = 1,2-benzoquinone monoimine
isophenoxazine = 2-aminophenoxazin-3-one
Other name(s): isophenoxazine synthase; o-aminophenol:O2 oxidoreductase; 2-aminophenol:O2 oxidoreductase; GriF
Systematic name: 2-aminophenol:oxygen oxidoreductase
Comments: A flavoprotein. While the enzyme from the plant Tecoma stans is activated by Mn2+ [1], that from the bacterium Streptomyces griseus (GriF) requires Cu2+ for maximal activity. Two molecules of the product 6-iminocyclohexa-2,4-dienone (i.e. 1,2-benzoquinone monoimine) spontaneously condense with oxidation to yield 2-aminophenoxazin-3-one [4]. 3-Amino-4-hydroxybenzaldehyde, which has a -CHO group at the para-position with respect to the hydroxy group of 2-aminophenol, was found to be the best substrate for GriF [4].
Links to other databases: BRENDA, EXPASY, KEGG, CAS registry number: 9013-85-8
References:
1. Nair, P.M. and Vaidynathan, C.S. Isophenoxazine synthase. Biochim. Biophys. Acta 81 (1964) 507-516.
2. Nair, P.M. and Vining, L.C. Isophenoxazine synthase apoenzyme from Pycnoporus coccineus. Biochim. Biophys. Acta 96 (1965) 318-327. [PMID: 14298835]
3. Subba Rao, P.V. and Vaidyanathan, C.S. Studies on the metabolism of o-aminophenol. Purification and properties of isophenoxazine synthase from Bauhenia monandra. Arch. Biochem. Biophys. 118 (1967) 388-394. [PMID: 4166439]
4. Suzuki, H., Furusho, Y., Higashi, T., Ohnishi, Y. and Horinouchi, S. A novel o-aminophenol oxidase responsible for formation of the phenoxazinone chromophore of grixazone. J. Biol. Chem. 281 (2006) 824-833. [PMID: 16282322]