Electron spin resonance--spin stabilization in enzymatic systems: detection of semiquinones produced during peroxidatic oxidation of catechols and catecholamines

The electron spin resonance-spin stabilization technique has been applied in an enzymatic system. This technique, which generates radicals in high steady-state concentration under static conditions, involves the use of limited quantities of enzyme and substrate while allowing facile spectral interpretation. In this work $\text{o}$-semiquinone intermediates produced during peroxidase-catalyzed oxidation of catechols and catecholamines have been detected as their metal complexes with Zn²⁺. No significant effect on the peroxidase activity was found for the concentrations of Zn²⁺ ions employed.