Partial purification of potato tuber invertase and its proteinaceous inhibitor

Improved purification of potato tuber invertase was achieved by utilizing a form of affinity chromatography between the enzyme and Concanavalin A (Con A) bound to Sepharose. Twenty-fold increases in specific activity were routinely obtained with this step and the enzyme was purified 190-fold over that found in the crude homogenate. The Con A-Sepharose chromatography step gave a greater purification than any other step in the invertase isolation procedure. There was up to 170% recovery of the activity loaded onto the column. α-Methyl-d-mannoside, sucrose, d-glucose and d-fructose eluted the enzyme from the Con A-Sepharose column with similar recoveries, although the volume of eluent required varied with the sugar. This unusually high recovery of invertase activity was obtained with some batches of tubers but not with others. There was evidence to suggest that the high recovery, or activation, may be due to the release of an inhibitor from the enzyme in the presence of Con A-Sepharose. Adsorption of invertase to Con A-Sepharose could be eliminated by incubation of the enzyme with α-mannosidase and β-glucosidase, indicating that potato tuber invertase is a glycoprotein. Proteinaceous inhibitor purification was improved by treatment of the tuber extract at low pH.