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 microM Km. Preincubation with the nitric oxide donor nitroprusside and dithiothreitol, elicited dose- and time-dependent, severalfold increase of Km and decrease of Vmax. At saturating ADP-ribose concentrations, fluoride was a strong inhibitor (IC50 approximately equal to 10-20 microM), 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 Vmax 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.