Identification of an enzyme in protein extracts of potato ( Solanum tuberosum L.) tubers which interferes with the assay of fructokinase and other enzymes requiring phosphorylated nucleosides

Abstract

An enzyme has been identified in protein extracts of potato tubers and which interferes with the assay of fructokinase and other kinases. The enzyme was partially purified and characterised and, on the basis of its properties, identified as apyrase (EC 3.6.1.5), a soluble nucleoside triphosphate diphosphohydrolase. Apyrase readily hydrolyses ATP during the course of the assay generating Pi, ADP and AMP. The latter two act as competitive inhibitors with respect to ATP during the assay of fructokinase activity. Apyrase was also shown to interfere with the assay of other enzymes, which use phosphorylated nucleosides as substrates, including hexokinase, ADPglucose pyrophosphorylase, 6-phosphofructokinase and pyruvate kinase. Given the broad range of substrates used by apyrase (ATP, ADP, UTP and UDP were all hydrolysed), it is suggested that the presence of apyrase might interfere with the assay of a range of enzymes which utilise phosphorylated nucleosides or are allosterically regulated by the products of their hydrolysis.