CHARACTERIZATION OF A BIS(5'-NUCLEOSIDYL) TRIPHOSPHATE PYROPHOSPHOHYDROLASE FROM ENCYSTED EMBRYOS OF THE BRINE SHRIMP ARTEMIA

1. A P1,P3-his(5'-nucleosidyl)triphosphate pyrophosphohydrolase (Np3Na se) has been partially purified from Artemia embryos. 2. The Np3 Nase has a native M(r) of 115,000 and preferentially hydrolyses substrates of the form Np3N. Relative rates of hydrolysis are Ap3A (V(rel) = 1.0) , Gp3G (V(rel) = 0.71), Ap4A (V(rel) = 0.08), Ap5A (V(rel) = 0.09), Gp 4G (V(rel) = 0.3) and Gp5G (V(rel) = 0.33). An NMP is always one of th e products. 3. The K(m) values for Ap3A and Gp3G are 15 and 10-mu-M re spectively. 4. Mg2+, Mn2+ and Ca2+ ions all stimulate the activity, wh ile Zn2+, Co2+ and Ni2+ ions are inhibitory. 5. The activity of the NP 3Nase remains constant during pre-emergence development of encysted em bryos but decreases slightly after hatching.