AN ISOPHENOXAZINE SYNTHASE FROM PYGNOPORUS COCCINEUS (FR.) BOND. AND SING.

Publisher Website
Google Scholar
Abstract
Mycelium from cultures of the red polypore Pycnoporus coccineus (Fr.) Bond. and Sing, contains an enzyme which catalyzes the oxidative condensation of 2 molecules of 2-aminophenol to yield 2-amino-3H-isophenoxazin-3-one. Fractionation of the crude extract has given a preparation with an 893-fold increase in specific activity. The purified enzyme has a pH optimum in citrate-phosphate buffer of 5.0, and a temperature optimum of 55°. The Kmvalue is 4.35 × 10−4 M. FMN and Mn++ions were required for maximum activity. FAD also served as an electron acceptor. Of the metal ions tested only Mn++activated the reaction. Hg++and Fe++inhibited strongly. The course of the reaction when cofactors were added separately suggested that flavin mononucleotide is the initial electron acceptor and that Mn++ions are required for reoxidation of the flavin. The enzyme has narrow specificity, and does not catalyze the oxidation of 3-hydroxyanthranilic acid, 3-hydroxykynurenine, or pyrocatechol.