Hydrolysis of triphosphoinositides by a soluble fraction of Crithidia fasciculata

Abstract

Homogenates of Crithidia fasciculata (a species of Trypanosomidae) were shown to contain a phosphatase (EC 3.1.3.36) and a phosphodiesterase (EC 3.1.4.11) which hydrolyse triphosphoinositides. Approximately 30% of the diesterase and most of the phosphatase are present in the soluble fraction. The triphosphoinositide phosphatase is specifically dependent upon Mg(2+) and is stable to storage with or without freezing. The triphosphoinositide phosphodiesterase requires Ca(2+) and is inactivated during storage. Both activities are maximal in the presence of cetyltrimethylammonium bromide and require protection or reactivation by GSH or dithiothreitol. Unlike similar mammalian enzymes the protozoal triphosphoinositide phosphatase does not hydrolyse diphosphoinositides. The two enzymes may be separated by (NH4)2SO4 fractionation and gel filtration on Sephadex G-200.