Characteristics of MgATP2--dependent electrogenic proton transport in tonoplast vesicles of the facultative crassulacean-acid-metabolism plant Mesembryanthemum crystallinum L. |
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Authors: | I Struve U Lüttge |
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Institution: | (1) Institut fur Botanik, Technische Hochschule Darmstadt, Schnittspahnstrasse 3-5, D-6100 Darmstadt, Federal Republic of Germany |
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Abstract: | Membrane vesicles were isolated from mesophyll cells of Mesembryanthemum crystallinum in the C3 state and in the crassulacean acid metabolism (CAM) state. The distribution of ATP-hydrolysis and H+-transport activities, and the activities of hydroxypyruvate reductase and Antimycin-insensitive cytochrome-c-reductase on continuous sucrose gradients was studied. For isolations carried out routinely a discontinuous sucrose gradient (24%/37%/50%) was used. Nitrate-sensitive ATP-hydrolysis and H+-transport activities increased several-fold during the transition from C3 photosynthesis to CAM. Nitrate-sensitive ATPase showed a substrate preference for ATP with an apparent Km (MgATP2-) of 0.19–0.37 mM. In both C3 and CAM states the ATPase showed a concentration-dependent stimulation by the anions chloride and malate. However, the pH optima of the two states were different: the ATPase of C3-
M. crystallinum had an optimum of pH 7.4 and that of CAM-M. crystallinum an optimum of pH 8.4. The optical probe oxonol-VI was used to demonstrate the formation of MgATP2--dependent electric-potential gradients in tonoplast vesicles.Abbreviations Bistris-Pronane
1,3-bis tris(hydroxymethyl)-methylaminol propane
- CAM
Crassulacean acid metabolism
- DIDS
4,4-dilsothiocyano-2,2-stilbene disulfonic acid:
- DTT
dithiothreitol
- ER
endoplasmic reticulum
- Hepes
4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid
- HPR
hydroxypyruvate reductase
- IDPase
inosine 5 -diphosphatase
- OX-VI
oxonol VI
- Tris
2-amino-2-(hydroxymethyl)-1,3-propanediol |
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Keywords: | ATP hydrolysis Crassulacean acid metabolism (induction) Membrane potential (tonoplast) Mesembryanthemum (H+ transport) Mg2+ ATPase Proton transport |
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