Specific ADP-ribose pyrophosphatase from Artemia cysts and rat liver: Effects of nitroprusside, fluoride and ionic strength

One specific ADP-ribose pyrophosphatase (ADPRibase) has been identified in Artemia cysts, following a protocol that in rat liver allows the identification of three ADPRibases. Artemia ADPRibase resulted similar, but not identical, to rat liver ADPRibase-I with respect to known and novel properties disclosed in this work. In the presence of Mg2+, Artemia ADPRibase was highly specific for ADP-ribose and showed a low, 0.7 mu M K-m. Preincubation with the nitric oxide donor nitroprusside and dithiothreitol, elicited dose- and time-dependent, severalfold increase of K-m and decrease of V-max. At saturating ADP-ribose concentrations, fluoride was a strong inhibitor (IC50 approximate to 10-20 mu M), whereas bringing ionic strength to 0.3-1.3 mol/l doubled the activity measured at lower or higher strengths. The novel fluoride and ionic strength effects were studied also with rat liver ADPRibase-I. Differences between the Artemia enzyme and ADPRibase-I concerned molecular weight (31 000 versus 38 500, respectively), Mn2+ ability to substitute for Mg2+ as the activating cation (better for the rat enzyme), and V-max decrease by nitroprusside (not seen with the rat enzyme). The results are discussed in relation with the role of specific ADPRibases as protective factors limiting free ADP-ribose accumulation and protein glycation, and as targets for cytotoxic agents.