Purification and heat stability of Cox's apple pulp peroxidase isoenzymes

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Abstract
Summary: Three peroxidase isoenzymes, two anionic and one cationic, were isolated from extracts of apple pulp using gel filtration and ion‐exchange chromatography. The homogeneity of the purified isoenzymes was established by isoelectric focusing and staining for peroxidase activity. The isoenzymes varied in their heat stability: the anionic isoenzymes were found to be more heat stable than the cationic isoenzyme. The measured enzymic activity of the isoenzymes was greatest when o‐dianisidine was used as the test substrate. After heating solutions of the anionic isoenzymes at 80–100°C for 2 min, up to 80% of the original enzymic activity was observed to regenerate when the heat‐treated isoenzymes were held at 30°C for 1 hr. Regeneration of enzymic activity following heat inactivation was not observed for the cationic isoenzyme.