Biotechnologie, Agronomie, Société et Environnement (Jan 2006)
Purification et caractérisation de deux phosphatases acides du tubercule de taro Xanthosoma sp. et leur rôle dans la conservation post-récolte
Abstract
Purifi cation and caracterization of two acid phosphatases from cocoyam tuber (Xanthosoma sp.) and its role on postharvesting preservation. Two forms of acid phosphatases (EC 3.1.3.2) were purifi ed from enzymatic crude extract of cocoyam tuber Xanthosoma sp., «atoumbou oronô» variety. This variety of cocoyam is cultivated and eaten in south and south-East areas of Côte dʼIvoire. These two phosphatases (PI and PII) exhibiting maximum activities at pH respectively 5.4 and 5.8 were purifi ed to homogeneous by polyacrylamide gel electrophoresis in native conditions. In SDS-PAGE, PI and PII showed each other one band with molecular weights of 25,000 and 22,000 respectively. In gel fi ltration, the molecular weights of the two acid phosphatases PI and PII were estimated to 30,000 and 25,000 respectively. These two acid phosphatases were inhibited by Hg2+ and Mo7+ ions and chemicals as DTNB (Dithionitrobenzoic acid), pCMB (4-Chloromercuribenzoic acid) and EDTA (Ethylenediaminetetraacetic acid). However they were activated by Mg2+ and Ca2+. The KM values were 0.72 and 0.30 mM respectively for PI and PII with pNPP (4-Nitrophenyl phosphate). These two acid phosphatases are also able to hydrolyze at different proportions other natural phosphorylated substrates like glucose-1-phosphate, galactose-1-phosphate, glucose-6- phosphate and NADP. PI hydrolyzed ATP but not PII. The two acid phosphatases hydrolyzed pyrophosphate. However, PI [KM = 0.61 mM and catalytic effi ciency (Vmax/KM = 213)] made it better than PII, it suggests that pyrophosphate should be one of the physiological substrates of this acid phosphatase involved in the metabolic process during the post-harvesting preservation of cocoyam tuber.
