Acid-labile ATP and/or ADP/P(i) binding to the tetraprotomeric form of Na/K-ATPase accompanying catalytic phosphorylation-dephosphorylation cycle.
The Na/K-ATPase has been shown to bind 1 and 0.5 mol of (32)P/mol of alpha-chain in the presence [gamma-(32)P]ATP and [alpha-(32)P]ATP, respectively, accompanied by a maximum accumulation of 0.5 mol of ADP-sensitive phosphoenzyme (NaE1P) and potassium-sensitive phosphoenzyme (E2P). The former accumulation was followed by the slow constant liberation of P(i), but the latter was accompanied with a rapid approximately 0.25 mol of acid-labile P(i) burst. The rubidium (potassium congener)-occluded enzyme (approximately 1.7 mol of rubidium/mol of alpha-chain) completely lost rubidium on the addition of sodium + magnesium. Further addition of approximately 100 microM [gamma-(32)P]ATP and [alpha-(32)P]ATP, both induced 0.5 mol of (32)P-ATP binding to the enzyme and caused accumulation of approximately 1 mol of rubidium/mol of alpha-chain, accompanied by a rapid approximately 0.5 mol of P(i) burst with no detectable phosphoenzyme under steady state conditions. Electron microscopy of rotary-shadowed soluble and membrane-bound Na/K-ATPases and an antibody-Na/K-ATPase complex, indicated the presence of tetraprotomeric structures (alphabeta)(4). These and other data suggest that Na/K-ATP hydrolysis occurs via four parallel paths, the sequential appearance of (NaE1P:E.ATP)(2), (E2P:E.ATP:E2P:E. ADP/P(i)), and (KE2:E.ADP/P(i))(2), each of which has been previously referred to as NaE1P, E2P, and KE2, respectively.
Yokoyama
T
T
Biological Chemistry, Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan.
Kaya
S
S
Abe
K
K
Taniguchi
K
K
Katoh
T
T
Yazawa
M
M
Hayashi
Y
Y
Mârdh
S
S
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002384:Catalysis; D004285:Dogs; D006868:Hydrolysis; D008956:Models, Chemical; D010710:Phosphates / Q000378:metabolism*; D010766:Phosphorylation; D011487:Protein Conformation; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine
D010710:Phosphates; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase