Effects of W-7, W-5, Verapamil and Diltiazem on vacuolar proton transport. Comparison of vacuolar H+-ATPase and H+-PPase from roots of Zea mays |
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Authors: | Wolfgang Pfeiffer |
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Institution: | Inst. für Pflanzenphysiologie der Univ., Hellbrunner Straβe 34, A-5020 Salzburg, Austria |
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Abstract: | The vacuolar membrane of plant cells is characterized by two proton pumps: the vacuolar H+-ATPase (V-ATPase; EC 3.6.1.3) and the vacuolar H+-PPase (V-PPase; EC 3.6.1.1). Recently, Du Pont and Morrissey reported that Ca2+ stimulates hydrolytic activity of purified V-ATPase (Arch. Biochim. Biophys., 1992. 294: 341–346). Since this effect may be due to degradation during purification further investigation of Ca2+ regulation of native V-ATPase was done. However, native tonoplast membranes contain a Ca2+/H+ antiport activity, which interferes with effects of calcium ions on proton transport activity of vacuolar ATPase. Therefore, the effects of anti-calmodulin drugs (W-7, W-5, calmidazolium), and calcium channel antagonists (Verapamil, Diltiazem) on proton transport activities of the vacuolar-type H+-ATPase and H+-PPase in tonoplast enriched membrane vesicle preparations from roots of Zea mays L. were studied. The concentrations for half maximal inhibition of vacuolar H+-ATPase (H+-PPase) were: 71 (191) μM W-7, 470 (> 800) μM W-5, 26 (24) μM calmidazolium (= compound R 24571). 398 (700) μM Verapamil, and 500 (1 330) μM Diltiazem. Estimation of Hill coefficients (nH) for the inhibition by Verapamil showed a further difference between the two vacuolar proton pumps (H+-ATPase, nH= 2.02; H+-PPase, nn= 0.96). The data indicate that the vacuolar H+-ATPase itself is affected by these chemicals. It is suggested that some biological activities of W-7, W-5, Verapamil, and Diltiazem are due to their effects on proton translocation by the vacuolar-type H+-ATPase. |
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Keywords: | Calmidazolium calmodulin antagonists Diltiazem H+-ATPase H+-PPase vacuolar proton pumps Verapamil W-7 W-5 |
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