PEROXIDASE ACTIVITY IN SATUREJA HORTENSIS L. ROOTS

Peroxidases have diverse functions in plant life such as defense against pathogen, cross-linking of cell wall components, formation of lignin and suberin, axin catabolism, and antioxidant defense. Because of the antioxidant properties found in savory (Satureja hortensis L.), it is important to characterize the peroxidases present in this labiatae. An extract from Satureja hortensis L. roots was obtained and peroxidase activity was determined by following the H₂O₂-mediated oxidation of o-dianisidine, guaiacol, ascorbate, ferulic acid and ABTS in the presence of extract aliquots. Apparent Km and Vmax were 0.11 ± 0.01 mM and 0.72 ± 0.04 mM.min^-1 (mg protein)^-1 for o-dianisidine at pH 5.5, 2.7 ± 0.2 mM and 0.24 ± 0.01 mM.min^-1 (mg protein)^-1 for guaiacol at pH 6.5, 0.2 ± 0.05 mM and 0.09 ± 0.01 mM.min^-1 (mg protein)^-1 for ascorbate at pH 8.0, 0.055 ± 0.005 mM and 1.64 ± 0.095 mM.min^-1 (mg protein)^-1 for ferulic acid at pH 5, and 0.28 ± 0.02 mM and 0.21 ± 0.02 mM.min^-1 (mg protein)^-1 for ABTS at pH 4.0. Catalytic efficiencies (calculated per mg protein in the extract) were 6.5 ± 0.2 min^-1 (mg protein)^-1 for o-dianisidine, 0.087 ± 0.004 min^-1 (mg protein)^-1 for guaiacol, 0.445 ± 0.045 min^-1 (mg protein)^-1 for ascorbate, 30 ± 2 min^-1 (mg protein)^-1 for ferulic acid and 0.75 ± 0.03 min^-1 (mg protein)^-1 for ABTS. All peroxidase activities were sensitive to KCN, with IC50 of 1 μM for o-dianisidine, 0.3 μM for guaiacol, 3.6 mM for ascorbate, 0.5 μM for ferulic acid and 15 μM for ABTS. Results point out the importance of peroxidase isoenzymes in the roots of Satureja hortensis L., notably the predominance of lignin peroxidase and the comparatively low activity of ascorbate peroxidase.