Mechanism responsible for oligomycin-induced occlusion of Na+ within Na/K-ATPase.
The mechanism whereby oligomycin occludes Na+ within Na/K-ATPase was investigated to study Na+ and K+ transport mechanisms. Oligomycin stimulated Na+ binding to Na/K-ATPase but inhibited Na-K and Na-Na exchange. The oligomycin concentration required to stimulate Na+ binding to half-maximal was 4.5 microM, which was close to the concentration that reduced Na-Na and Na-K exchange and ATPase activity to half-maximal, suggesting that Na/K-ATPase possesses an oligomycin binding site responsible for stimulating Na+ binding and reducing ion exchange and ATPase activity. In contrast, neither K+ binding nor K+ transport was affected by oligomycin. Limited tryptic digestion of Na/K-ATPase showed that, unlike Na+, K+, and ouabain, oligomycin treatment did not result in a specific digestion pattern. Oligomycin appeared to inhibit ouabain binding in a noncompetitive manner, whereas it did not affect ATP binding. Na/K-ATPase isoforms with low and high sensitivities to ouabain were equally sensitive to oligomycin. These results suggest that the oligomycin binding site is located on the extracellular side of Na/K-ATPase, at a different position from the ouabain binding site, and this antibiotic did not induce a conformational change of Na/K-ATPase. We propose that oligomycin interacts with the Na+ occlusion site from the extracellular side of Na/K-ATPase, which delays Na+ release to the extracellular side without inducing a conformational change, suggesting that the pathways responsible for Na+ and K+ transport differ.
Arato-Oshima
T
T
Second Department of Biochemistry, Kyorin University School of Medicine, Mitaka, Tokyo 181, Japan.
Matsui
H
H
Wakizaka
A
A
Homareda
H
H
D000818:Animals; D001665:Binding Sites; D002417:Cattle; D004285:Dogs; D007668:Kidney / Q000201:enzymology*; D007679:Kidney Medulla / Q000201:enzymology; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D008961:Models, Structural; D009840:Oligomycins / Q000378:metabolism / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D011188:Potassium / Q000378:metabolism; D011487:Protein Conformation; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry* / Q000378:metabolism*
D009840:Oligomycins; D010446:Peptide Fragments; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium