title: Diadenosine tetraphosphate hydrolase from mouse liver. Purification to homogeneity and partial characterization.
abstract: An enzyme hydrolyzing diadenosine 5',5"'P1, P4-tetraphosphate (Ap4A) to AMP and ATP has been purified to apparent homogeneity from mouse liver cell extracts. The isolation procedure comprised ammonium sulfate precipitation, chromatography on Sephadex G-75. DEAE-cellulose, blue Sepharose and AMP-Sepharose. The enzyme is a single polypeptide chain with a native Mr = 64,000 with a Km of 1.66 microM and Vmax of 1.25 mumol/min. AMP, ADP, Ap4, GTP, Gp4, Ap3A, Ap5A, Gp3G, and Gp5G are noncompetitive inhibitors of the Ap4A hydrolase activity, whereas Gp4G inhibits Ap4A hydrolysis competitively with a Ki of 6 microM. Theophylline, caffeine, and isobutylmethylxanthine do not or only slightly inhibit Ap4A hydrolysis. Mitogenic factors have no effect on the enzymatic activity of Ap4A hydrolase, excluding that a direct influence of internalized mitogens on Ap4A degradation could be responsible for mitogen-dependent fluctuation of intracellular Ap4A pool sizes.
mesh_terms: D017766:Acid Anhydride Hydrolases; D000818:Animals; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D051379:Mice; D008970:Molecular Weight; D010744:Phosphoric Monoester Hydrolases / Q000302:isolation & purification* / Q000378:metabolism; D012265:Ribonucleotides / Q000494:pharmacology; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D012265:Ribonucleotides; D013439:Sulfhydryl Reagents; D010744:Phosphoric Monoester Hydrolases; D017766:Acid Anhydride Hydrolases; C020023:bis(5'-nucleosyl)tetraphosphatase (asymmetrical)