Prartial Purification and Some Properties of ADP-glucose Phosphorylase from Potato Tubers

Abstract

ADP-glucose phosphorylase [adenosine diphosphate glucose: orthophosphate adenylyltransferase; Dankert et al., Biochim. Biophys. Acta, 81, 78 (1964)] was found to be widely distributed in plant tissues. The enzyme was purified 570-fold in a 24% yield from cell-free extract of growing tubers of potato (Solanum tuberosum L.). The following reaction catalyzed by the purified enzyme was found to proceed stoichiometrically.
ADP-glucose+P₁→ADP+glucose-l-P
Maximal activity was observed at pH 8. The enzyme was the most stable at pH 7, showing 50% loss of its original activity after 50min heating at 57°C. The following kinetic parameters were obtained: activation energy, 11.1 kcal/mole; Km (P₁), 2.5mM; Km (ADP-glucose), 0.05mM. The enzyme did not act on GDP-mannose, GDP-glucose and UDP-glucose. Neither activator nor inhibitor was found among various phosphorylated metabolites tested. The enzyme was inhibited by metal-binding reagents, EDTA and o-phenanthroline. None of the metal ions tested was found to recover the activity of chelator-treated enzyme.