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.