LACCASE-MEDIATED FORMATION OF THE PHENOXAZINONE DERIVATIVE, CINNABARINIC ACID

The phenoxazinone chromophore occurs in a variety of biological system s, including numerous pigments and certain antibiotics. It also appear s to form as part of a mechanism to protect mammalian tissue from oxid ative damage. During cultivation of the basidiomycete, Pycnoporus cinn abarinus, a red pigment was observed to accumulate in the culture medi um. It was identified as the phenoxazinone derivative, cinnabarinic ac id (CA). Laccase was the predominant extracellular phenoloxidase activ ity in P. cinnabarinus cultures. In vitro studies showed that CA was f ormed after oxidation of the precursor, 3-hydroxyanthranilic acid (3-H AA), by laccases. Moreover, oxidative coupling of 3-HAA to form CA was also demonstrated for the mammalian counterpart of laccase, the blue copper oxidase, ceruloplasmin.