Abstract
The bafilomycin A
1 and N-ethylmaleimide (NEM)-sensitive (V-type) ATPase was partially purified from the apical membrane-rich fractions of excretory system (Malpighian tubules and hind gut) of
P. bufonius. Enzymatic activity was inhibited by bafilomycin A
1 (IC
50 = 1.3 nM) and NEM (IC
50 = 10.1 μM). The V-type ATPase activity is confined to the apical membrane fraction, while the activity of Na
+/K
+ -ATPase forms the major part of the basal membrane fraction. The optimal pH required for maximal activity of V-type ATPase was pH 7.5. The effect of 30 mM of various salts on ATPase activity was investigated. NaCl and KCl caused increases of 175% and 184%, respectively. Other chloride salts also caused an increase in activity in the following ascending order: RbCl, LiCI, choline Cl, NaCI, KCl and
tris-HCl. The activity of V-type ATPase was stimulated by a variety of different anions and cations, and HCO
3
– was found to be the most potent cationic activator of ATPase activity. The present results show that the properties of V-type ATPase of
P. bufonius are similar to those reported for other insect tissues.