A K+-dependent phosphatase in the membranes of low-K+-type erythrocytes

Abstract 1. 1. A small K + -dependent fraction of p -nitrophenylphosphatase activity has been demonstrated in LK-type ruminant red cell ghosts. 2. 2. The K + -dependent enzyme has a K m of abut 3.3 mM for p -nitrophenylphosphate, and shows substrate inhibition. 3. 3. This phosphatase is stimulated by the anti-L antibody, without any measurable change in the apparent affinity for K + . 4. 4. Addition of 20 mM Na + + 10 μM ATP causes an increase in phosphatase activity at low concentrations, followed by inhibition as the K + concentration is increased. Anti-L treated cells show an increased (Na + + ATP)-dependent stimulation but without change in the reactivity towards K + . 5. 5. The K + -sensitive phosphatase is inhibited 50% by 1 mM ouabain in the absence, and 90% in the presence of (ATP + Na + ).