Abstract
The apparent affinity constants for the binding of Cs+, Rb+, K+, Li+, Tl+ and NH4+ to (Na+ + K+)-dependent ATPase [EC 3.6.1.3] from teleost [Anguilla anguilla] gills were measured and the values discussed in terms of the ion-selectivity isotherm described by Eisenman et Krasne (1975). The ion selectivity of the present enzyme is remarkably similar to that from nerve and brain.