Kinetic Studies on a Brain Microsomal Adenosine Triphosphatase. Evidence Suggesting Conformational Changes^*

The interaction of potassium ions and ATP on the sodium pump of resealed red cell ghosts.

“…2 shows that increasing ATP increases the Rb influx and, not surprisingly, the Rb influx is much greater at 200 fM than at D. A. EISNER AND D. E. RICHARDS at about 100 /sM-ATP, the influx at 10/M-Rb is half-saturated by 10 /zM-ATP. These results are therefore in agreement with those of Robinson (1967) on the isolated Na+-K+ ATPase in showing that the apparent affinity for ATP depends on the concentration of K. Furthermore, they show that at least part of the effect of K is at the external site.…”

Purification and Functional Characterization of a Low‐Molecular‐Mass Na+ K+‐ATPase Inhibitor Protein from Rat Brain Cytosol

“…Na ', K+-ATPase activity was assayed as described before [20,211. Briefly, the reaction mixture in a volume of 400 p1 containing 30 mM histidine, 25 mM sucrose and 1 mM EDTA, pH 7.5, 3 mM MgCI,, 10 pg protein with or without 130 mM NaCl and 20 mM KC1 was incubated at 37°C for 5 min.…”

Affinity of the (Na+ + K+)‐dependent ATPase for Na+ measured by NA+‐modified enzyme inactivation

“…Inactivation was terminated and residual activity measured by adding 4 vol of media to bring the concentrations of reactants to their standard assay concentrations: 30 mM histidine HC1 (adjusted to pH 7.8 with Tris), 3 mM ATP, 3 mM MgC12, 90 mM NaC1, and 10 mM KC1. ATPase activity was measured during this incubation, for 4-8 min 0 at 37 C., in terms of the production of P i, as previously described [6]. Inactivation was calculated relative to control activity, measured concurrently, representing corresponding preincubation and incubation conditions but without DCCD.…”