Conversion of isophenoxazine to catechol in Tecoma stans

Abstract

Isophenoxazine, formed by the condensation of two molecules of ο-aminophenol, is reduced by an enzyme system from Tecoma stans leaves to two molecules of catechol. The reaction proceeds well under anaerobic conditions; a 1-2 mole stoichiometry between the substrate disappeared and the product formed was maintained. The enzyme showed maximum activity at ρH 5. The substrate at high concentrations caused a diminution in the activity and the optimum concentration of substrate was at 6 × 10^-4m. The enzyme preparation was able to convert cinnabarinic acid and diphenylene dioxide 2,3-quinone into the corresponding catechol substances. The diphenylene dioxide 2,3-quinone at the same concentration was three times more susceptible to enzymic cleavage than isophenoxazine. Cinnabarinic acid inhibited the enzymic cleavage of isophenoxazine competitively. None of the known electron donors was found to activate the reaction. Inhibition studies suggested that intact sulfhydryl groups are necessary for enzyme activity. Heavy metal ions like Hg⁺⁺, Ag⁺, Co⁺⁺, Fe⁺⁺, Ni⁺⁺, and Fe³⁺⁺ inhibited the reaction. Metal chelating agents did not have any effect on the enzyme.