Studies of high potassium and low potassium sheep erythrocyte membrane sodium-adenosine triphosphatase. Interactions with oligomycin, adenosine triphosphate, sodium, and potassium.

The effects of oligomycin on Na+-ATPase of high K (HK) and low K (LK) sheep erythrocyte membranes have been investigated. Activation of LK Na+-ATPase is observed with ATP 5 0.2 pM; activation of HK is observed with ATP 5 0.02 PM. Inhibition occurs with higher ATP. At 0.2 pM ATP, oligomycin stimulation of LK Naf-ATPase is associated with a 3to 4-fold increase in the 3ZP-“intermediate;” inhibition of HK is associated with only a slight increase (1.3-fold) in 32P-“intermediate.” The effects of oligomycin are similar for HK and LK in that activation occurs at low catalytic rates (5 20 pmoles mg-l min-I); inhibition occurs at higher rates, irrespective of the means of altering the rate (varying ATP or Na+ concentration, or both; stimulation of LK with specific isoimmune antiserum). Oligomycin counteracts K+-inhibition (LK) and K+ counteracts oligomycin inhibition (HK). The results are consistent with a reaction sequence involving oligomycin-sensitive conformational changes of phosphorylated and probably unphosphorylated intermediate, i.e. EiP + EOP and Ei + E,,; the resulting shift in equilibrium can, at low catalytic rates, be evidenced in stimulation of Na+-ATPase. Interaction of HK and LK Na+-ATPase with Naf, K+, and ATP are interdependent and markedly different for the two; at constant ATP (0.2 KM), HK is more sensitive to activation by Na+ and less sensitive to inhibition by K+ than LK ATPase. Although effects of both Kf and oligomycin are dependent on ATP concentration, a difference in affinity for ATP in addition to, or as a result of, a different relative affinity for Naf and K+ may be the basis for the distinctions between HK and LK membranes.