Properties of the V-type ATPase from the excretory system of the usherhopper, Poekilocerus bufonius
2002
Al-Fifi, Z.I.A. | Al-Robai, A. | Khoja, S.M.
The bafilomycin A1 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 A1 (IC50 = 1.3 nM) and NEM (IC50 = 10.1 micromolar). 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, LiCl, choline Cl, NaCl, KCl and tris-HCl. The activity of V-type ATPase was stimulated by a variety of different anions and cations, and HCO3(-) 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.
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