THE CELL-WALL LOCALIZATION OF 2 STRONGLY BASIC ISOPEROXIDASES IN ETIOLATED LUPINUS-ALBUS HYPOCOTYLS AND ITS SIGNIFICANCE IN CONIFERYL ALCOHOL OXIDATION AND INDOLE-3-ACETIC-ACID CATABOLISM

Two strongly basic peroxidase (EC 1.11.1.7) isoenzymes, B3 and B4, of isoelectric points 9.5 and 9.7, are localized in cell walls of young Lupinus albus hypocotyls. The binding of B3 and B4 isoenzymes to cell walls is specific and, unlike that observed for acidic isoperoxidases, is maximal at neutral pH values. By comparison with A1 and A2 acidic isoperoxidases, cell wall-bound basic B3 and B4 isoperoxidases are little involved in coniferyl alcohol oxidation and indole-3-acetic acid catabolism. However, due to the localization of these isoenzymes in vacuoles also, they are probably involved in some type of H2O2-dependent oxidation reaction common to both lytic compartments. These results are discussed on the basis of a possible participation of these isoenzymes, as indicated by other authors, in the oxidative transformation of tetracyclic bisquinolizidine-type alkaloids in lupin.