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 identifie d 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 an d novel properties disclosed in this work. In the presence of Mg2+, Ar temia ADPRibase was highly specific for ADP-ribose and showed a low, 0 .7 mu M K-m. Preincubation with the nitric oxide donor nitroprusside a nd dithiothreitol, elicited dose- and time-dependent, severalfold incr ease of K-m and decrease of V-max. At saturating ADP-ribose concentrat ions, 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 activit y measured at lower or higher strengths. The novel fluoride and ionic strength effects were studied also with rat liver ADPRibase-I. Differe nces between the Artemia enzyme and ADPRibase-I concerned molecular we ight (31 000 versus 38 500, respectively), Mn2+ ability to substitute for Mg2+ as the activating cation (better for the rat enzyme), and V-m ax decrease by nitroprusside (not seen with the rat enzyme). The resul ts are discussed in relation with the role of specific ADPRibases as p rotective factors limiting free ADP-ribose accumulation and protein gl ycation, and as targets for cytotoxic agents.