Three peroxidase isoenzyme-groups found in cell walls of tobacco were tested for their capacity to form H2O2. Isoenzyme-group GI, located only in cell walls (GIIand GIIIare also found in protoplasts) showed the highest Kapp-value for H2O2-formation. The lowest Kapp-value, i.e., maximal H2O2-formation was received for group GIIIwhich is ionically bound to the cell wall. As shown before, GIyields maximal polymerization rates for coniferyl- and p-coumarylalcohol. These facts indicate that each of the peroxidase isoenzyme groups of the cell wall is involved with different catalytic functions within the same pathways of H2O2-formation and succeeding lignification. H2O2-formation catalyzed by all 3 groups was increased by very low concentrations of Mn2+-ions. The required amount of Mn2+leading to maximal stimulation was in each case dependent on the basic rate of H2O2-formation. Maximal stimulation of H2O2-formation by phenolic compounds was achieved by coniferylalcohol at a concentration of 10-4M for all groups. Stimulation by p-coumaryl-and by sinapylalcohol was not as significant.
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