ADP Is a Competitive Inhibitor of ATP-Dependent H Transport in Microsomal Membranes from Zea mays L. Coleoptiles |
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| Authors: | Rausch T Ziemann-Roth M Hilgenberg W |
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| Affiliation: | Botanisches Institut der J. W. Goethe-Universität, Siesmayerstrasse 70, 6000-Frankfurt, Federal Republic of Germany |
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| Abstract: | An anion-sensitive ATP-dependent H+ transport in microsomal membranes from Zea mays L. coleoptiles was partially characterized using the pH gradient-dependent decrease of unprotonated neutral red. The following criteria strongly suggest a tonoplast origin of the H+ transport observed: strict dependence on Cl−; inhibition by SO42− and NO3−; insensitivity against vanadate, molybdate, and azide; reversible inhibition by CaCl2 (H+/Ca2+ antiport); inhibition by diethylstilbestrol. The substrate kinetics revealed simple Michaelis Menten kinetics for ATP in the presence of 1 millimolar MgCl2 with a Km value of 0.56 millimolar (0.38 millimolar for MgATP). AMP and c-AMP did not influence H+ transport significantly. However, ADP was a potent competitive inhibitor with a Ki value of 0.18 millimolar. The same inhibition type was found for membranes prepared from primary roots by the same procedure. |
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