Igamberdiev Abir U, Kleczkowski Leszek A
Department of Plant Science, Faculty of Agriculture and Food Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2.
Biochim Biophys Acta. 2003 Dec 8;1607(2-3):111-9. doi: 10.1016/j.bbabio.2003.09.005.
Concentrations of adenylate species and free magnesium (Mg(2+)) within cells are mediated by the equilibrium governed by adenylate kinase (AK), the enzyme abundant in plants in chloroplast stroma and intermembrane spaces of chloroplasts and mitochondria. Ratios of free and Mg-bound adenylates (linked to the values of [Mg(2+)] established under AK equilibrium) can be rationalized in terms of the overall dependence of concentrations of Mg(2+) and free and Mg-bound adenylates, as well as electric potential values across the inner membranes of mitochondria and chloroplasts. The potential across the inner mitochondrial membrane, by driving adenylate translocators, equilibrates free adenylates across the inner membrane according to the Nernst equation and contributes to the ATP(total)/ADP(total) ratio in the cytosol. The ratio affects the exchange of free adenylates with chloroplasts and this, in turn, influences the value of potential across the inner chloroplast membrane. From measurements of subcellular ATP(total)/ADP(total) ratios, we suggest a method of estimating the values of potential across inner membranes of mitochondria and chloroplasts in vivo, which allows a comparison of the operation of these organelles under different physiological conditions. We discuss also how the equilibration of adenylates by AK drives adenylate transport across membranes, and establishes [Mg(2+)] in the cytosol and chloroplast stroma, maintaining the rates of photosynthesis and respiration. This provides a tool for metabolomic research, by which the determined concentrations of adenylate species could be used for computation of essential metabolic parameters in the cell and in subcellular compartments.
细胞内腺苷酸种类和游离镁（Mg(2+)）的浓度由腺苷酸激酶（AK）所控制的平衡介导，AK是一种在植物叶绿体基质以及叶绿体和线粒体的膜间隙中大量存在的酶。游离腺苷酸与镁结合腺苷酸的比例（与AK平衡下建立的[Mg(2+)]值相关）可以根据Mg(2+)、游离腺苷酸和镁结合腺苷酸的浓度以及线粒体和叶绿体内膜两侧的电势值的总体依赖性来解释。线粒体内膜两侧的电势通过驱动腺苷酸转运体，根据能斯特方程使内膜两侧的游离腺苷酸达到平衡，并有助于细胞质中ATP（总量）/ADP（总量）的比例。该比例影响游离腺苷酸与叶绿体之间的交换，进而影响叶绿体内膜两侧的电势值。通过对亚细胞ATP（总量）/ADP（总量）比例的测量，我们提出了一种在体内估计线粒体和叶绿体内膜两侧电势值的方法，这使得在不同生理条件下对这些细胞器的运行情况进行比较成为可能。我们还讨论了AK介导的腺苷酸平衡如何驱动腺苷酸跨膜运输，并在细胞质和叶绿体基质中建立[Mg(2+)]，维持光合作用和呼吸作用的速率。这为代谢组学研究提供了一种工具，通过该工具，所测定的腺苷酸种类浓度可用于计算细胞和亚细胞区室中的基本代谢参数。
