title: Heat inactivation and reactivation of broccoli peroxidase.
abstract: Heat inactivation characteristics differed for acidic (A), neutral (N), and basic (B) broccoli peroxidase. At 65 degrees C, A was the most heat stable followed by N and B. The activation energies for denaturation were 388, 189, and 269 kJ/mol for A, N, and B, respectively. Reactivation of N occurred rapidly, within 10 min after the heated enzyme was cooled and incubated at room temperature. The extent of reactivation varied from 0 to 50% depending on the isoenzyme and heating conditions (temperature and time). The denaturation temperature allowing the maximum reactivation was 90 degrees C for A and horseradish peroxidase (HRP) and 70 and 80 degrees C for B and N, respectively. In all cases, heat treatment at low temperatures for long times prevented reactivation of the heated enzymes. Calcium (5 mM) increased the thermal stability of N and B but had no effect on reactivation. The presence of 0.05% bovine serum albumin decreased thermal stability but increased the extent of reactivation of A..
authors.affiliation: Department of Food Science and Technology, University of California, One Shields Avenue, Davis, California 95616-8598, USA.
authors.forename: Tipawan
authors.initials: T
authors.lastname: Thongsook
authors.forename: Diane M
authors.initials: DM
authors.lastname: Barrett
mesh_terms: D001937:Brassica / Q000201:enzymology*; D002118:Calcium / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D004793:Enzyme Reactivators; D004795:Enzyme Stability / Q000187:drug effects; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000378:metabolism; D009195:Peroxidase / Q000378:metabolism*; D012710:Serum Albumin, Bovine / Q000494:pharmacology
chemical_list: D004793:Enzyme Reactivators; D007527:Isoenzymes; D012710:Serum Albumin, Bovine; D004533:Egtazic Acid; D009195:Peroxidase; D002118:Calcium