Isolation and thermostability of peroxidase isoenzymes from apple cultivars Gala and Fuji

Extracts of soluble peroxidase and ionically-bound peroxidase were obtained from the peel and pulp of apples (Mallus comunis), cultivars Gala and Fuji, using 100 mM sodium phosphate buffer and pH 6.0 and 7.0 for pulp and peel of Gala cultivar, respectively and pH 5.5 for the pulp and the peel of cultivar Fuji. Then the enzymatic activity of peroxidase (POD) was determined in both extracts, soluble fractions and ionically-bound. Electrophoresis results shows similar compositions for the anionic and cationic isoenzymes in both cultivars. The molecular weights and pI values of the isolated isoenzymes from the Fuji cultivar were: two anionic, A1 and A2 (38, 28 kDa and pI 4.4; 5.0, respectively) and three cationic C1, C2 and C3 (40, 34, 26 kDa and pI 8.0, 8.3, 9.0, respectively). From the Gala cultivar, also, two anionic isoenzymes were isolated A2 and A4 (28, 26 kDa and pI 5.0 and 5.7, respectively) and three cationic isoenzymes C1, C2 and C3 (40, 34, 26 kDa and pI 8.0, 8.3 and 9.0, respectively). The cationic isoenzymes were more heat-stable under the heat treatments at 65, 70, 75 and 80 °C in both cultivars.