Abstract Peroxidases from several plants, including horseradish peroxidase, were capable of converting flavonols to the corresponding 2,3-dihydroxyflavanones in presence of H2O2 . Contrastingly, protein extracts from Mentha piperita plants and Mentha arvensis cell suspension cultures perform ed the same enzymatic step in absence of H2O2 , but only with quercetin, not with kaempferol. H2O2-independent, quercetin converting enzymes were isolated and purified from these extracts, and they could be classified in two groups according to the extent of stimulation of the enzyme reaction by H2O2 . Enzymes from group I were stimulated by exogenous H2O2 , and they resembled horse radish peroxidase in several aspects. They possessed IAA oxidase activity, but quercetin was the preferred substrate. Enzymes from group II from the plants appeared to be a distinctly different set of enzymes. They were not stimulated by H2O2 , but required molecular oxygen and converted only 3,3′,4′-trihydroxyflavones under aerobic conditions. Also, they showed no Soret-bands and possessed no IAA oxidase activity. These proteins appear to be a new class of enzymes participating in the first step of flavonol degradation in plants.
Isolation and Characterization of Microprotoplasts from Propyzamide-treated Cell Suspension Cultures of Hemerocallis hybrida
