Diadenosine 5′,5‴-P1,P4-tetraphosphate hydrolase is present in human erythrocytes, leukocytes and platelets

Molecular Characterization and Mutational Analysis of Recombinant Diadenosine 5′,5″-P¹,P⁴-Tetraphosphate Hydrolase from <i>Plasmodium falciparum</i>

“…The low K m value of wild-type enzyme indicated that the Plasmodium enzyme has high affinity for Ap 4 A; this high substrate affinity was previously observed for Ap 4 A hydrolase isolated from both human erythrocytes (K m 0.7 µM) and leukocytes (K m 1.5 µM). 24) Several studies of Nudix hydrolases have referred to the importance of catalytic residues inside and adjacent to the catalytic motif. The principles of this catalytic mechanism appear to be well conserved among the Nudix hydrolases, including those of humans.…”

Human diadenosine triphosphate hydrolase: preliminary characterisation and comparison with the Fhit protein, a human tumour suppressor.

“…Protein extracts obtained by ammonium sulphate fractionation (40-80%) of platelet homogenates exhibit hydrolase activity on e-(Ap 3 A) and e-(Ap 4 A) due to Ap 3 Aase and asymmetrical Ap 4 Aase, respectively. The presence of asymmetrical Ap 4 Aase in human blood cells has previously been reported [19,21]. Hydrolase activity on e-(Ap 2 A), the substrate used to detect non-specific phosphodiesterase activity, was negligible.…”

“…Enzyme purification. Concentrates of human platelets (700 ml) were processed to eliminate other contaminating blood cells and to fractionate platelet protein between 40% and 80% of ammonium sulphate saturation according to [19]. The protein pellet after 80% ammonium sulphate precipitation was redissolved in 50 mM Hepes KOH, pH 7.0, 0.1 M KCl, 5% glycerol (26 ml), divided into three aliquots and each subjected to gel-filtration chromatography on a Sephacryl S-200 column (26 mm´900 mm) equilibrated in the same buffer and eluted at 2.0 ml/min.…”

Metabolic transformation of AZTp4A by Ap4A hydrolase regenerates AZT triphosphate

“…Since it has been demonstrated that the Ap 4 A hydrolase has limited specificity for the base and for whether the 2 -oxy or deoxy sugar is present, it was anticipated that it might be able to hydrolyze AZTp 4 A. Further, Ap 4 A hydrolase is widely distributed in mammalian tissues, having been identified in Ehrlich ascites tumor cells (Moreno et al, 1982), human leukemia cells (Ogilvie and Antl, 1983), human placenta (Lazewska et al, 1993), human erythrocytes, leukocytes, and platelets (Hankin et al, 1995). Hence, the metabolism of AZTp 4 A by Ap 4 A hydrolase could influence the effectiveness of AZT therapy.…”