Coupling Between ATP Hydrolysis and H+ Transport by ATPases in the Plasma Membrane and Tonoplast of Plant Cells

99220260 Spanswick本研究是一个项目的延续，该项目设计的长期目标是了解植物细胞中离子在植物细胞膜上运输的化学渗透方案。本提案中提出的具体问题是，观察到ATP水解和质子运输之间的耦合似乎是可变的，例如，取决于膜泡悬浮液中阴离子的浓度。涉及运输和atp酶活性之间的内在耦合（“滑移”）或电驱动的被动质子通量（“泄漏”）的假设将通过各种方法进行测试，以解释阴离子刺激atp酶介导的质子通量和atp酶活性之间的明显差异。盐在细胞内外以及单个细胞区室内外的适当分布对所有细胞的正常功能至关重要。本研究的长期目标是了解离子（如质子、钾和钠（盐的成分））在植物细胞膜上的运输机制，以维持它们的正态分布。这需要了解单个离子输运系统的性质。关于离子传输机制的一个有用的整体假设是基于一个方案，其中主要的主动传输系统是利用富含能量的分子ATP水解产生的能量，通过电化学梯度传输质子（氢离子）穿过细胞膜的酶。根据该方案，其他离子通过二级系统传输，二级系统的能量来源于质子的电化学梯度。（钙离子在质膜上的转运是个例外。）该项目的具体目标是详细研究ATP水解与质子在植物细胞外膜和细胞内腔室（细胞质）膜上的转运之间的关系。这项研究的结果应该提供一个基本的拼图，从长远来看，将导致对植物如何维持其盐平衡的完整理解。＊＊＊

99220260 Spanswick This research is the continuation of a program designed with the long term objective of understanding transport in plant cells in terms of a chemiosmotic scheme for the transport of ions across plant cell membranes. The specific problem addressed in this proposal is that raised by the observation that the coupling between ATP hydrolysis and proton transport by ATPases from both the plasma membrane and the tonoplast appears to be variable depending, for example, upon the concentration of anions present in the membrane vesicle suspension. Hypotheses involving intrinsic u coupling between transport and ATPase activity ("slip") or electrically driven passive proton fluxes ("leak") will be tested by a variety of methods to account for the apparent discrepancy between anion stimulation of ATPase-mediated proton fluxes and of ATPase activity. %%% A proper distribution of salts between the inside and outside of a cell and the inside and outside of individual cellular compartments is critical for the normal function of all cells. The long term goal of this research is to understand the transport mechanisms for ions such as protons, potassium, and sodium (the components of salts) across the membranes of plant cells to maintain their normal distributions. This requires understanding the properties of the individual ion transport systems. A useful overall hypothesis for the mechanism of ion transport is based on a scheme in which the primary active transport systems are enzymes that transport protons (hydrogen ions) across cell membranes against an electrochemical gradient, using energy from hydrolysis of the energy-rich molecule, ATP. According to this scheme, other ions are transported by way of secondary systems that derive their energy from the electrochemical gradient of protons. (Transport of calcium ions across the plasma membrane is an exception.) The specific goal of this project is to study in some detail the relation between ATP hydro lysis and proton transport across the plant cell outer membrane and the membrane of an intracellular compartment, the tonoplast. The results of this research should provide a fundamental piece of the puzzle that in the long run will result in a complete understanding of how plants maintain their salt balance. ***