An ouabain-sensitive Na+,K(+)-ATPase in tentacles of the sea anemone Stichodactyla helianthus

Tentacles of Stichodactyla helianthus contain an ouabain-inhibitable, (Na+,K+)-stimulated ATPase. The K0.5 for Na+ was 24 mM and for K+, 3.2 mM. The apparent affinity for ouabain was low, I50 = 10(-4) M. The order of cation affinities was Rb+ > K+ > NH4+ = Cs+. The catalytic subunit of the enzyme comprised a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, M(r) = 105 kDa, that was phosphorylated by [32P]ATP in the presence of NaCl and dephosphorylated by the addition of KCl. The alpha subunit was weakly reactive with antibodies directed against the rat alpha subunit.