Characteristics of MgATP2--dependent electrogenic proton transport in tonoplast vesicles of the facultative crassulacean-acid-metabolism plantMesembryanthemum crystallinumL.
✍ Scribed by I. Struve; U. Lüttge
- Publisher
- Springer-Verlag
- Year
- 1987
- Tongue
- English
- Weight
- 1010 KB
- Volume
- 170
- Category
- Article
- ISSN
- 0032-0935
No coin nor oath required. For personal study only.
✦ Synopsis
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 ATPhydrolysis 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 (MgATP 2-) of 0.19-0.37 raM. 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 MgATPZ--dependent electric-potential gradients in tonoplast vesicles.