Figure 3.

Sequential mixing stopped-flow fluorescence transients of Na⁺,K⁺-ATPase from shark rectal gland noncovalently labeled with RH421. All experimental conditions were as described in Fig. 1. The number of averaged transients and the F values for double-exponential fits to the data were: 0.2 mM K⁺ (17 transients, F = 148), 2 mM K⁺ (19 transients, F = 3167), 5 mM K⁺ (14 transients, F = 1416), and 20 mM K⁺ (15 transients, F = 404). The K⁺ concentrations are all after mixing.