IDENTIFICATION OF AN ENZYME IN PROTEIN EXTRACTS OF POTATO (SOLANUM-TUBEROSUM L.) TUBERS WHICH INTERFERES WITH THE ASSAY OF FRUCTOKINASE ANDOTHER ENZYMES REQUIRING PHOSPHORYLATED NUCLEOSIDES

An enzyme has been identified in protein extracts of potato tubers and which interferes with the assay of fructokinase and other kinases. Th e enzyme was partially purified and characterised and, on the basis of its properties, identified as apyrase (EC 3.6.1.5), a soluble nucleos ide triphosphate diphosphohydrolase. Apyrase readily hydrolyses ATP du ring the course of the assay generating Pi, ADP and AMP. The latter tw o act as competitive inhibitors with respect to ATP during the assay o f fructokinase activity. Apyrase was also shown to interfere with the assay of other enzymes, which use phosphorylated nucleosides as substr ates, including hexokinase, ADPglucose pyrophosphorylase, 6-phosphofru ctokinase and pyruvate kinase. Given the broad range of substrates use d by apyrase (ATP, ADP, UTP and UDP were all hydrolysed), it is sugges ted that the presence of apyrase might interfere with the assay of a r ange of enzymes which utilise phosphorylated nucleosides or are allost erically regulated by the products of their hydrolysis. (C) 1998 Elsev ier Science Ireland Ltd. All rights reserved.