An Approach to the Characterization of Betanine Oxidation Catalyzed by Horseradish Peroxidase

Abstract

Horseradish peroxidase (HRP, EC 1.1.11.7) catalyzed oxidation of betanine is complex, as judged by the shape of the consecutive absorption spectra of the reaction medium. Graphic analysis of these spectra by a matricial test revealed the presence of at least three kinetically related absorbent species in the reaction mixture. Analysis by HPLC confirmed the presence of several reaction products. During the course of the reaction, a red intermediate and several yellow products, presumably of a polymeric nature, are generated, betalamic acid being one of the final products. Even in the absence of enzyme, the reaction, once initiated, continued again, yielding betalamic acid as a final product, which is formed as both substrate and intermediate product disappear. The chemical nature of the intermediate product and the possible reaction mechanism are discussed. Keywords: Beta vulgaris; betanine oxidation; peroxidase; red beet