Purification of Glucose Oxidase and Catalase Produced by the Apple Blue Mold, Penicillium expansum O-385-10, and Their Characteristics Including the Browning of Apple Fruit

Penicillium expansumO-385-10 produces glucose oxidase and catalase but showed poorgrowth in medium containing glucose as a sole carbon source. In this culture, gluconate wasaccumulated, the pH of the culture medium decreased during incubation, and growth wasremarkably inhibited. Glucose oxidase and catalase were purified as electrophoreticallyhomogeneous proteins from the culture in which the pH was adjusted using calcium carbonate.The molecular weights of glucose oxidase and catalase were estimated at about 130 kDa (homodimer) and 300 kDa (homotetramer). Glucose oxidase and catalase showed about 80%and 50% activity at pH 3, respectively. The catalase was remarkably activated by 1mM Ca2+and 1mM Ba2+. When glucose oxidase and catalase were simultaneously incubated withsmall pieces of apple, the fruit tissue browned remarkably. No browning reaction occurredwhen each enzyme was incubated independently.