The human non-gastric H,K-ATPase has a different cation specificity than the rat enzyme.
The primary sequence of non-gastric H,K-ATPase differs much more between species than that of Na,K-ATPase or gastric H,K-ATPase. To investigate whether this causes species-dependent differences in enzymatic properties, we co-expressed the catalytic subunit of human non-gastric H,K-ATPase in Sf9 cells with the beta(1) subunit of rat Na,K-ATPase and compared its properties with those of the rat enzyme (Swarts et al., J. Biol. Chem. 280, 33115-33122, 2005). Maximal ATPase activity was obtained with NH(4)(+) as activating cation. The enzyme was also stimulated by Na(+), but in contrast to the rat enzyme, hardly by K(+). SCH 28080 inhibited the NH(4)(+)-stimulated activity of the human enzyme much more potently than that of the rat enzyme. The steady-state phosphorylation level of the human enzyme decreased with increasing pH, [K(+)], and [Na(+)] and nearly doubled in the presence of oligomycin. Oligomycin increased the sensitivity of the phosphorylated intermediate to ADP, demonstrating that it inhibited the conversion of E(1)P to E(2)P. All three cations stimulated the dephosphorylation rate dose-dependently. Our studies support a role of the human enzyme in H(+)/Na(+) and/or H(+)/NH(4)(+) transport but not in Na(+)/K(+) transport.
Swarts
Herman G P
HG
Department of Biochemistry, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
Koenderink
Jan B
JB
Willems
Peter H G M
PH
De Pont
Jan Joep H H M
JJ
D000251:Adenosine Triphosphatases / Q000032:analysis / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000641:Ammonia / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D020134:Catalytic Domain; D002412:Cations; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics; D017506:H(+)-K(+)-Exchanging ATPase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008274:Magnesium / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D009840:Oligomycins / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010766:Phosphorylation; D011188:Potassium / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012964:Sodium / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D013045:Species Specificity; D018411:Spodoptera / Q000166:cytology / Q000378:metabolism
D002412:Cations; D004791:Enzyme Inhibitors; D007093:Imidazoles; D009840:Oligomycins; D021122:Protein Subunits; D011994:Recombinant Proteins; C035235:Sch 28080; D010042:Ouabain; D000641:Ammonia; D012964:Sodium; D000251:Adenosine Triphosphatases; D017506:H(+)-K(+)-Exchanging ATPase; D008274:Magnesium; D011188:Potassium