EPR DETECTION OF PHYTOPHENOXYL RADICALS STABILIZED BY ZINC IONS - EVIDENCE FOR THE REDOX COUPLING OF PLANT PHENOLICS WITH ASCORBATE IN THE H2O2-PEROXIDASE SYSTEM

Chlorogenic acid (CGA; 3-o-caffeoylquinic acid), a phenylpropanoid met abolite of plants, was oxidized by H2O2 in the presence of horseradish peroxidase. The primary and secondary oxidized products both were fre e radicals which gave EPR multiline signals at g = 2.0044 and 2.0042 i n the presence of zinc as a spin stabilizing agent. The EPR kinetics s howed that ascorbate functioned as a cooperative reductant by regenera ting CGA from its corresponding radicals. These results provide eviden ce to support the idea that the ascorbate-phenolic redox couple in con junction with guaiacol peroxidase is an efficient H2O2 scavenging mech anism in higher plants. (C) 1998 Federation of European Biochemical So cieties.