Mechanism of inhibition of horseradish peroxidase by cyclopropanone hydrate.

Cyclopropanone hydrate irreversibly inactivates horseradish peroxidase in a time-dependent manner in the presence of oxidizing agent, hydrogen peroxide. The inhibition reaction is a second order reaction of cyclopropanone hydrate with compound I, the 2 electron-oxidized form of peroxidase, and results in covalent modification of the heme cofactor. A new propionic acid side chain is substituted for one of the methine protons of the heme. A mechanism for inhibition is proposed to involve oxidative ring opening of cyclopropanone hydrate to give the primary free radical of propionic acid, which subsequently alkylates the heme. An isoporphyrin pi cation intermediate is predicted by this mechanism, and this intermediate has been detected spectroscopically.