Purification and properties of a unique flavin-containing chloroperoxidase from the capitellid polychaete Notomastus lobatus

Abstract

A unique flavin-containing chloroperoxidase from the marine worm Notomastus lobatus was purified to homogeneity. This enzyme is composed of two dissociable protein moieties, a flavoprotein and a heme protein, in 1:1 molar ratio. The flavoprotein (Mr = 120,000) consists of four identical subunits having Mr of 30,000, and contains FAD. The heme protein (Mr = 54,000) is composed of two copies each of two non-identical subunits (Mr = 15, 500 and 11, 500) and contains ferriheme. The native N. lobatus chloroperoxidase (Mr = 174,000) therefore has a structure of alpha 4 beta 2 gamma 2. Neither the flavoprotein nor the heme protein alone has detectable chloroperoxidase activity but readily associate to form fully active enzyme. This enzyme is capable of oxidizing Cl-, Br-, and I- with optimum pH values of 4.5, 5.0, and 4.5, respectively, at 440 microM H2O2 and has halide-independent catalase activity in the absence of organic substrate. The enzyme can halogenate a wide variety of aromatic compounds, including phenol, from which it produces 4-bromophenol, 2,4-dibromophenol, and 2,4,6-tribromophenol. The same compounds are found in N. lobatus. The N. lobatus chloroperoxidase is the first haloperoxidase to be purified to homogeneity from a marine polychaete, the first reported to contain flavin, and has several unusual physical and catalytic properties. This chloroperoxidase appears to represent a new class of haloperoxidases.