KINETICS OF PAPAYA PECTINESTERASE

Purified papaya (Carica papaya L. var. exotica) pectinesterase (EC 3.1 .1.11) was investigated for its activity as a function of NaCl, pH and temperature, and determination of its kinetic parameters. The activit y was linear up to 20 min with an enzyme concentration of up to 6.14 m u g. Optimum activity was obtained with 0.25 M NaCl concentration and the optimum pH was found to be 8. The energy of activation of enzyme w as 5690 cal mol(-1). A Q(10) of 1.29 was observed in the temperature r ange of 30-50 degrees C and the optimum temperature for the enzyme act ivity was 65 degrees C. The K-m value for citrus pectin was 0.11 mg/ml , corresponding to a V-max value of 730 mu mole/min/mg protein. The tu rnover number was calculated as 23 360 mole/(mole.min). Enzyme activit y was found to be inhibited by the addition of polygalacturonic acid, alginic acid and sucrose in the reaction mixture and their K-i values were calculated as 0.019 mg/ml, 0.17 mg/ml and 29%, respectively. Poly galacturonic acid was found to act as a competitive inhibitor whereas alginic acid and sucrose showed a competitive-non-competitive and unco mpetitive type of inhibition, respectively.