DEOXYCHOLATE STIMULATION OF GOLDFISH INTESTINAL (NA++K+)-ATPASE AND ITS RELATION TO DIGOXIN BINDING

1. 1. Low concentrations of deoxycholate inhibit Mg2+-activated ATPase, enahnce the (Na+ + K+)-activated ATPase and leave unchanged the total ATPase activity of goldfish intestinal membrane preparations. 2. 2. Tritiated digoxin has been shown to bind to the membrane preparation. A large part of the total digoxin bound (approx. 65%) was dependent on the presence of Mg2+ + Na+ + ATP, and this fraction has been taken to represent digoxin specifically bound to the (Na+ + K+)-activated ATPase. 3. 3. The deoxycholate-induced change sin (Na+ + K+)-ATPase activity are not accompanied by parallel changes in digoxin binding. 4. 4. There is a marked incrase in the catalytic centre activity of the (Na+ + K+)-ATPase at high deoxycholate concentrations (1.25-2.5 mM). 5. 5. It is concluded that deoxycholate inhibition of Mg2+-ATPase is not associated with its transformation to the (Na+ + K+)-activated enzyme. The deoxycholate activation of (Na+ + K+)-ATPase probably represents an increase in the effective turnover rate of a fixed number of enzyme sites. © 1969.