EFFECT OF TEMPERATURE AND PH ON ATP HYDROLYSIS BY DUCK SALT-GLAND NA-ATPASE(,K+)

The shape of the substrate curve during ATP hydrolysis by duck salt gl and Na+,K+-ATPase was found to depend on experimental conditions. Unde r optimal conditions (pH 7.4, 37 degrees C) the curve has an intermedi ary plateau in the range of 0.7-0.9 mM ATP. Both acidification of the medium and decrease in incubation temperature (below 20 degrees C) tra nsform this curve into a simple hyperbole characteristic of GTP or UTP hydrolysis, having no modifying effect on the enzyme. We recently sug gested that the deviation from Michaelis-Menten kinetics during ATP hy drolysis is explained by the formation of short-lived oligomeric compl etes during the hydrolytic cycle of the enzyme. We interpret the data in terms of the idea that the studied factors affect interprotomer int eractions in the Na+,K+-ATPase oligomers.