The beta-subunits of Na+,K+-ATPase and gastric H+,K+-ATPase have a high preference for their own alpha-subunit and affect the K+ affinity of these enzymes.
The alpha- and beta-subunits of Na+,K+-ATPase and H+,K+-ATPase were expressed in Sf9 cells in different combinations. Immunoprecipitation of the alpha-subunits resulted in coprecipitation of the accompanying beta-subunit independent of the type of beta-subunit. This indicates cross-assembly of the subunits of the different ATPases. The hybrid ATPase with the catalytic subunit of Na+,K+-ATPase and the beta-subunit of H+,K+-ATPase (NaKalphaHKbeta) showed an ATPase activity, which was only 12 +/- 4% of the activity of the Na+,K+-ATPase with its own beta-subunit. Likewise, the complementary hybrid ATPase with the catalytic subunit of H+,K+-ATPase and the beta-subunit of Na+,K+-ATPase (HKalphaNaKbeta) showed an ATPase activity which was 9 +/- 2% of that of the recombinant H+,K+-ATPase. In addition, the apparent K+ affinity of hybrid NaKalphaHKbeta was decreased, while the apparent K+ affinity of the opposite hybrid HKalphaNaKbeta was increased. The hybrid NaKalphaHKbeta could be phosphorylated by ATP to a level of 21 +/- 7% of that of Na+,K+-ATPase. These values, together with the ATPase activity gave turnover numbers for NaKalphabeta and NaKalphaHKbeta of 8800 +/- 310 min-1 and 4800 +/- 160 min-1, respectively. Measurements of phosphorylation of the HKalphaNaKbeta and HKalphabeta enzymes are consistent with a higher turnover of the former. These findings suggest a role of the beta-subunit in the catalytic turnover. In conclusion, although both Na+,K+-ATPase and H+,K+-ATPase have a high preference for their own beta-subunit, they can function with the beta-subunit of the other enzyme, in which case the K+ affinity and turnover number are modified.
Koenderink
J B
JB
Department of Biochemistry, Institute of Cellular Signaling, University of Nijmegen, P. O. Box 9101, 6500 HB Nijmegen, The Netherlands.
Swarts
H G
HG
Hermsen
H P
HP
De Pont
J J
JJ
D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D002384:Catalysis; D017506:H(+)-K(+)-Exchanging ATPase / Q000737:chemistry / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000378:metabolism*; D018411:Spodoptera; D013270:Stomach / Q000201:enzymology*
D011994:Recombinant Proteins; D017506:H(+)-K(+)-Exchanging ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium