(Na +-K +)-activated ATPase in isolated mucosal cells of toad bladder

Abstract

1. 1. A method is described for reproducible measurement of ATPase activity in isolated mucosal cells of toad bladder. 47 ± 7 % (S.D.) of the total activity is Na +- and K +-dependent, and yields 22 ± 5 (S.D.) μmoles P i per mg protein per h. 2. 2. The curve depicting this enzymatic activity as a function of Na + concentration is sigmoid in shape, suggesting cooperative interaction between binding sites for cations. 3. 3. Graded doses of ouabain were preincubated without ATP with the enzyme for 10 min. In deoxycholate-treated preparations, half-maximal inhibition was seen at 10 −4 M and complete inhibition at ⩾ 10 −3 M. In the absence of deoxycholate, 39 % of the activity persisted even at 10 −2 M ouabain.