28] Inosine diphosphatase (nucleoside diphosphatase) from mammalian liver: Nucleoside diphosphate + H2O → nucleoside monophosphate + orthophosphate

Abstract

Publisher Summary This chapter discusses the extraction of inosine diphosphatase (IDP or nucleoside diphosphatase) from mammalian liver. In the assay method, the enzymatic liberation of orthophosphate from a susceptible nucleoside diphosphate is determined. IDP is used as the substrate for routine work, because, at the moment, it is less expensive than other hydrolyzable nucleotides, such as uridine diphosphate (UDP) or guanosine diphosphate (GDP). The enzyme from beef or calf liver does not catalyze the dephosphorylation of ATP, ITP, ribose 5-triphosphate, IMP, AMP, ADP, or CDP. The relative activities with IDP, UDP, and GDP are 1, 1.7, and 1.6 with purified enzyme from beef liver, and the relative rates of hydrolysis of IDP, UDP, GDP, and ribose 5-pyrophosphate are about 1.0, 0.6, 0.8, and 0.6 with the enzyme from calf liver. A preparation from lamb liver has been reported to hydrolyze thiamine pyrophosphate slowly. The optimal action of the enzyme from beef liver is at pH 6.9. The activity at pH 6.45 or 7.4 is only 10 to 15% lower than at the optimum.