|
Everted membrane vesicles of Helicobacter pylori were prepared and the membrane-resided ATPases were characterized. For comparison, Escherichia coli membrane ATPases and hog gastric mucosal H,K-ATPase were employed. ATPase assay revealed that the composite enzyme pool was relatively low in specific activities, below 1/10 times than that found in E. coli. According to their inhibitory specificities, most of the ATPase pool appeared to belong to the P-type ATPase, sensitive to vanadate but not to azide. The enzyme pool was extraordinarily resistant against treatment by N,N´-dicyclohexylcarbodiimide (DCCD). Certain monovalent cations, e.g., K^+ or NH_4^+ stimulated the whole enzyme pool only in the presence of Mg^2+. On the contrary, Ni^2+ and Zn^2+ increased enzyme activity rather effectively without the aid of Mg^2+. Under a defined condition employed, H. pylori cells could retain the membrane ATPase pool to the extent of 17% at pH 3.2. Moreover, its activity was most stable in acidic conditions (pH 5.4∼6.4). However, cytoplasmic or peripheral ATPase pools were hardly detected under acidity (below pH 4.6).
|