Characterization of recombinant TbrPPX1. Panel A: Michaelis-Menten kinetics with pentasodium triphosphate as substrate. Each assay point was done in triplicate (standard deviations are too small to be visible in the graph). A representative graph of three independent experiments is shown. Panel B: Sodium pyrophosphate is neither a substrate for, nor an inhibitor of TbrPPX1. Enzyme reactions were run in the absence (triangles) or presence (squares) of 100 mM petasodium triphosphate, and with increasing concentrations of sodium pyrophosphate. Panel C: Influence on TbrPPX1 activity (at 100 μM sodium pentaphosphate) by 1: H2O (control); 2: 1 mM sodium pyrophosphate; 3: 1 mM cAMP; 4: 1 mM of each dATP, dCTP, dGTP and TTP; 5: 300 mg/ml tRNA; 6: 100 u/ml heparin; 7: 200 u/ml heparin, 8: 10 mM arginine, and 9: 10 mM EDTA. Panel C: Inhibition of TbrPPX1 by Zn2+ in the presence of 1 mM MgCl2.