Conversion of Chl a into Chl d by horseradish peroxidase

Abstract

We report for the first time on the Chl a into Chl d conversion with horseradish peroxidase in aqueous acetone at room temperature in the dark, both in the presence and absence of hydrogen peroxide, H2O2. After 48 h incubation, the Chl d formation from Chl a catalyzed by horseradish peroxidase was observed in acetone/water (10/1, v/v) even in the absence of H2O2, where the conversion yield, 0.1%, was much lower than that observed in the case of papain, 2%. Very fast conversion occurred with the combination of horseradish peroxidase and dilute H2O2 (acetone/0.3% H2O2 = 10/1, v/v); the yield reached up to 1% for 2 h incubation. However, the converted Chl d was then gardually degraded probably due to the oxidation power of H2O2. In contrast, such a rapid conversion was not observed in the case of papain, where the conversion yield was, rather, depressed from 2% down to 0.2% by H2O2. These results suggest that chemical mechanisms for the Chl a into Chl d conversion catalyzed by papain and horseradish peroxidase are essentially different from each other, which will provide new insight into the unsolved question as to the birth of Chl d in nature.