Lupin peroxidases. I. Isolation and characterization of cell wall‐bound isoperoxidase activity

Cell wall fragments, isolated from dark‐grown Lupinus albus L. (cv. multolupa) hypocotyls, and purified by washing with Triton X‐100, did not show detectable contamination by enzyme markers of cytosol or endoplasmic reticulum in which peroxidase activity was also located by electron microscopy. Peroxidase (EC 1.11.1.7) isoenzymes, solubilized from these cell wall fractions by high saline forces, showed a high affinity towards guaiacyl type substrates, whereas syringyl type substrates were not oxidized. On the other hand, both the isoenzyme patterns and the substrate specificity of these cell wall isoperoxidases could be altered by chromatographic and denaturating/renaturating procedures, which break the protein‐phenol interactions, and this suggests the presence of phenol‐induced conformers. These results draw attention to the origin of the enzymatic polymorphism, and catalytic properties, of the peroxidase activity located in the cell wall.