Acid phosphatase in the tubers of Dioscorea species and its purification from the white yam (D. rotundata poir)

Abstract

Acid phosphatase activity was determined in 15 cultivars from four species of yam. A 12-fold purification of the enzyme from Dioscorea rotundata (cv. chikakwondo) gave a homogeneous preparation as demonstrated by polyacrylamide gel electrophoresis. This enzyme preparation has an apparent molecular weight of 115 000 +2000 and an optimum activity at a p H of 5-20 and a temperature of 50°C. The K, ofthe enzyme is 3.81 m M with disodium p-nitrophenylphosphate (p-NNP) as a substrate. The energy of activation, heat of activation, energy of inactivation and heat of inactivation are 7.0, 6.4, 4.41 and 4.34 kcal M -~, respectively. Although it has very little activity with most organic phosphoric acid esters, it is significantly inhibited by Ca2+, Hg2+ and EDTA and activated by Mgz+.The enzyme has a half-life of 50,170r 13 days, respectively, when stored at W C , 0°C or room temperature (29+2"C).