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Three peroxidase fractions (peak I, II, III) were isolated from Fuji apples using CM-cellulose chromatography. The homogeneity of the isolated peroxidase isozymes was established by isoelectric focusing and electrophoresis. Isoelectric points of the isozymes were 3.80, 3.82, and 3.85, respectively. The optimum pH of peroxidase isozymes were pH 5.0(peak I) or 5.5(peak II, III), and optimum temperature was 40℃ when assayed by using guaiacol and H₂O₂ as substrates. Inactivation rate of three peroxidase isozymes were different at temperature of 70℃ and at pH of 5.5. The isozyme of peak II was found to be more heat stable than those of peak I and III. D values at 70℃ of peroxidase isozymes (peak I, II, III) were estimated to be 660 sec, 1,320 sec, and 600 sec, respectively. The thermal stability of Fuji apple peroxidase was not influenced in the presence of 0.032 M sucrose or lactose. However, the thermal stability of the enzyme was decreased by fructose and glucose.
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