Dual effect of ADP on the activity of the plasma membrane H+‐ATPase of red beet |
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Authors: | Roberto Papini Maria Ida De Michelis |
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Institution: | R. Papini and M. I. De Michelis (corresponding author, e‐mail;, present address: Univ. di Milano, Dipto di Biologia, Sez. Fisiol. Bioch. Piante, via G. Celoria 26 3C, I‐20133 Milano, Italy), Istituto Botanico dell' Univ. di Genova, corso Dogali 1c, I‐16136 Genova, Italy. |
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Abstract: | The effect of ADP on the activity of the plasma membrane (PM) H+‐ATPase of red beet ( Beta vulgaris L.) parenchyma discs was evaluated by analyzing the effect of increasing concentrations of ADP on the kinetics of the reaction. When the PM H+‐ATPase activity was assayed at pH 6.3, ADP behaved as a simple competitive inhibitor. When the activity was assayed at pH 7.1, ADP not only increased the apparent Km for MgATP but also decreased the Vmax of the reaction. When the C‐terminal domain of the PM H+‐ATPase was cleaved by controlled trypsin treatment or displaced by addition of lysophosphatidylcholine, only the competitive component of inhibition by ADP of the activity assayed at pH 7.1 was evident. The results are discussed in relation to the physiological relevance of the activation of the PM H+‐ATPase by displacement of the autoinhibitory C‐terminal domain. |
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Keywords: | Beta vulgaris inhibition by ADP plasma membrane H+‐ATPase red beet regulation |
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