title: Isolation and characterization of diadenosine 5',5"'-P1,P4-tetraphosphate pyrophosphohydrolase from Physarum polycephalum.
abstract: A new enzyme that hydrolyzes diadenosine 5',5"'-P1,P4-tetraphosphate has been purified by a factor of 250 from the acellular slime mold Physarum polycephalum. Activity was assayed radioisotopically with [3H]Ap4A. Isolation of the enzyme was facilitated by dye-ligand chromatography. The enzyme symmetrically hydrolyzes Ap4A to ADP and exhibits biphasic kinetics for the substrate with values for the apparent Km of 2.6 micro M and 37 micro M. The two values of Vmax differ by a factor of 10. Mg2+, Ca2+, and other divalent cations inhibit the activity with 40-80% inhibition occurring at 0.5 mM. Mg2+, at 0.5 mM, decreases both values of Vmax by 50%, decreases the low Km value by about 30%, and increases the high Km value by about 100%. (Ethylenedinitrilo)tetraacetic acid (EDTA) and [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA), at 10 mM, inhibit the activity by 50%. ADP, ATP, Ap4, and Gp4 are equipotent inhibitors with 50% inhibition occurring at 30 micro M. AMP is a relatively weak inhibitor. The molecular weight of the enzyme is 26000 on the basis of elution of activity from a calibrated Sephadex G-75 column.
mesh_terms: D017766:Acid Anhydride Hydrolases; D002413:Cations, Divalent; D007700:Kinetics; D008970:Molecular Weight; D010727:Phosphoric Diester Hydrolases / Q000302:isolation & purification* / Q000378:metabolism; D010804:Physarum / Q000201:enzymology*; D011487:Protein Conformation
chemical_list: D002413:Cations, Divalent; D010727:Phosphoric Diester Hydrolases; D017766:Acid Anhydride Hydrolases; C036849:bis(5'-nucleosyl)tetraphosphatase (symmetrical)