Characterisation of a bis(5'-nucleosidyl) triphosphate pyrophosphohydrolase from encysted embryos of the brine shrimp Artemia.

1. A P1,P3-bis(5'-nucleosidyl)triphosphate pyrophosphohydrolase (Np3 Nase) has been partially purified from Artemia embryos. 2. The Np3 Nase has a native Mr of 115,000 and preferentially hydrolyses substrates of the form Np3 N. Relative rates of hydrolysis are Ap3A (Vrel = 1.0), Gp3G (Vrel = 0.71), Ap4A (Vrel = 0.08), Ap5A (Vrel = 0.09), Gp4G (Vrel = 0.3) and Gp5G (Vrel = 0.33). An NMP is always one of the products. 3. The Km values for Ap3A and Gp3G are 15 and 10 microM respectively. 4. Mg2+, Mn2+ and Ca2+ ions all stimulate the activity, while Zn2+, Co2+ and Ni2+ ions are inhibitory. 5. The activity of the Np3 Nase remains constant during pre-emergence development of encysted embryos but decreases slightly after hatching.