Isolation and Characterization of Pectin Methylesterase from Apple Fruit

Two forms of the enzyme pectin methylesterase are evidenced in the apple ( Malus communis ). They differ both in their charge and molecular weight. The two enzymes were separated by DEAE‐cellulose chromatography. Their molecular weights, determined by gel‐filtration, were 55000 and 28000 daltons. The heavier form has been purified at homogeneity and subjected to investigations regarding its activity as a function of the pH and temperature, and determination of its kinetic parameters. The enzyme has a Km value of 1.05 mg/mL for citrus pectin and an optimum activity in the pH range between 6.5‐7.5. The enzyme was stable up to 40°C. Incubation for 1 min at 90°C leads to its complete inactivation.