Hydrolytic properties of the (Na+ + K+)-ATPase isozymes for beta-(2-furyl)acryloyl phosphate, a pseudosubstrate for the sodium pump.
The hydrolysis of beta-(2-furyl)acryloyl phosphate (FAP), a synthetic substrate for the (Na+ + K+)-ATPase by the partially purified enzyme from rat brain and rat kidney, has been assessed. Using previously determined FAPase reaction conditions, it was discovered that the KI for ouabain of the alpha 2/3 isozyme of the (Na+ + K+)-ATPase was approximately 10(-5) M, while for the alpha 1 isozyme the KI was approximately 10(-3) M. These values were an order of magnitude higher (lower affinity) than the KI's for ouabain as determined when using ATP in a coupled assay for (Na+ + K+)-ATPase activity: approximately 10(-6) M and approximately 10(-4) M for the alpha 2/3 and alpha 1 isozymes, respectively. This discrepancy was alleviated by altering established reaction conditions. Previously published FAPase studies have overlooked this fact, since either the properties of the isozymes of the (Na+ + K+)-ATPase were unknown at that time, or ouabain titration profiles were never performed.
Brodsky
J L
JL
Department of Biochemistry & Molecular Biology, Harvard University, Cambridge, MA 02138.
Guidotti
G
G
D000179:Acrylates / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000201:enzymology*; D007527:Isoenzymes / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D015222:Sodium Channels / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D012995:Solubility; D013379:Substrate Specificity
D000179:Acrylates; D007527:Isoenzymes; D015222:Sodium Channels; C025983:beta-(2-furyl)acryloyl phosphate; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase