Properties of the V-type ATPase from the excretory system of the usherhopper, Poekilocerus bufonius.
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 microM). 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.
Al-Fifi
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ZI
King Abdulaziz University, Faculty of Science, Department of Biological Sciences, P.O. Box 80203, Jeddah 21589, Saudi Arabia. z_alfifi@hotmail.com
Al-Robai
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Khoja
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D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D005260:Female; D006430:Hemiptera / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D018942:Macrolides; D008297:Male; D012492:Salts; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D004791:Enzyme Inhibitors; D018942:Macrolides; D012492:Salts; C040929:bafilomycin A1; D000255:Adenosine Triphosphate; D025262:Vacuolar Proton-Translocating ATPases; D005033:Ethylmaleimide