title: Direct evidence for an ADP-sensitive phosphointermediate of (K+ + H+)-ATPase.
abstract: Direct evidence for the occurrence of an ADP-sensitive phosphoenzyme of (K+ + H+)-ATPase, the proton-pumping system of the gastric parietal cell is presented. The enzyme is phosphorylated with 5 microM [gamma-32P]ATP in 50 mM imidazole-HCl (pH 7.0) and in the presence of 7-15 microM Mg2+. Addition of 5 mM ADP to this preparation greatly accelerates its hydrolysis. We have been able to establish this by stopping the phosphorylation with radioactive ATP, by adding 1 mM non-radioactive ATP, which leads to a slow monoexponential process of dephosphorylation of 32P-labeled enzyme. The relative proportion of the ADP-sensitive phosphoenzyme is 22% of the total phosphoenzyme. Values for the rate constants of breakdown and interconversion of the two phosphoenzyme forms have been determined.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D004492:Edetic Acid / Q000494:pharmacology; D005753:Gastric Mucosa / Q000201:enzymology*; D017506:H(+)-K(+)-Exchanging ATPase; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D010766:Phosphorylation; D011485:Protein Binding; D013552:Swine
chemical_list: D000244:Adenosine Diphosphate; D004492:Edetic Acid; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase