The energy transduction mechanism is different among P-type ion-transporting ATPases. Acetyl phosphate causes uncoupling between hydrolysis and ion transport in H+,K(+)-ATPase.
H+,K(+)-ATPase, Na+,K(+)-ATPase, and Ca(2+)-ATPase belong to the P-type ATPase group. Their molecular mechanisms of energy transduction have been thought to be similar until now. Ca(2+)-ATPase and Na+,K(+)-ATPase are phosphorylated from both ATP and acetyl phosphate (ACP) and dephosphorylated, resulting in active ion transport. However, we found that H+,K(+)-ATPase did not transport proton nor K+ when ACP was used as a substrate, resulting in uncoupling between energy and ion transport. ACP bound competitively to the ATP-binding site of H+,K(+)-ATPase. The hydrolysis of ACP by H+,K(+)-ATPase was stimulated by cytosolic K+, the half-maximal stimulating K+ concentration (K0.5) being 2.5 mM, whereas the hydrolysis of ATP was stimulated by luminal K+, the K0.5 being 0.2 mM. Furthermore, during the phosphorylation from ACP in the absence of K+, the fluorescence intensity of H+,K(+)-ATPase labeled with fluorescein isothiocyanate increased, but those of Na+,K(+)-ATPase and Ca(2+)-ATPase decreased. These results indicate that phosphorylated intermediates of H+,K(+)-ATPase formed from ACP are not rich in energy and that there is a striking difference(s) in the mechanism of energy transduction between H+,K(+)-ATPase and other cation-transporting ATPases.
Asano
S
S
Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Japan.
Kamiya
S
S
Takeguchi
N
N
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D001692:Biological Transport; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004734:Energy Metabolism; D005453:Fluorescence; D017506:H(+)-K(+)-Exchanging ATPase; D006868:Hydrolysis; D010755:Organophosphates / Q000494:pharmacology*; D010766:Phosphorylation; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D010755:Organophosphates; C011632:acetyl phosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase