From A H, Zimmer S D, Michurski S P, Mohanakrishnan P, Ulstad V K, Thoma W J, Uğurbil K
Department of Medicine, Minneapolis Department of Veterans Affairs Medical Center, Minnesota.
Biochemistry. 1990 Apr 17;29(15):3731-43. doi: 10.1021/bi00467a020.
The mechanisms that underlie the balance between the consumption and oxidative generation of ATP in the intact cell are not well-defined. Cytosolic inorganic phosphate (Pi) and ADP levels, the cytosolic ATP/ADP ratio, and the cytosolic phosphorylation potential (PP) have all been proposed as major regulatory variables, the latter as a component of a "near-equilibrium" thermodynamic regulatory scheme. Therefore, the potential regulatory roles of these variables in the intact cell were evaluated with 31P NMR and Langendorff perfused rat hearts; in this preparation, the tissue oxygen consumption rate (MVO2) can be varied over a wide range. When the exogenous carbon source was varied, none of the proposed regulatory parameters, i.e., the ATP/ADP ratio, PP, or cytosolic ADP level, were found to be uniquely related to MVO2. Rather, ADP levels at a given MVO2 decreased progressively for the exogenous carbon sources in the following order: glucose, glucose + insulin, palmitate + glucose, lactate, pyruvate + glucose, and octanoate + glucose. In the octanoate and pyruvate groups, MVO2(-1) was linearly dependent upon [ADP]-1 with apparent Km values being in the range previously observed in isolated mitochondria. A similar trend was observed in the MVO2-[Pi] relationship. The present findings suggest that exogenous carbon sources which effectuate deregulation of intramitochondrial NADH generation lower cytosolic ADP and Pi to levels which are limiting to the rate of oxidative phosphorylation. For other carbon sources, the processes controlling the rate of NADH generation also participate in determining the rate of oxidative ATP synthesis. However, this control must be exerted kinetically rather than through a near-equilibrium thermodynamic mechanism as indicated by the present data and prior kinetic studies of the ATP synthetic process in both isolated mitochondria and intact myocardium [La Noue, K. F., et al. (1986) Biochemistry 25, 7667-7675; Kingsley-Hickman, P., et al. (1987) Biochemistry 26, 7501-7510].
完整细胞中ATP消耗与氧化生成之间平衡的潜在机制尚未明确界定。胞质无机磷酸盐（Pi）和ADP水平、胞质ATP/ADP比率以及胞质磷酸化电位（PP）都被认为是主要的调节变量，后者是“近平衡”热力学调节方案的一个组成部分。因此，利用31P NMR和Langendorff灌注大鼠心脏评估了这些变量在完整细胞中的潜在调节作用；在这种制备方法中，组织氧消耗率（MVO2）可以在很宽的范围内变化。当改变外源碳源时，未发现任何提出的调节参数，即ATP/ADP比率、PP或胞质ADP水平与MVO2有唯一关联。相反，对于给定的MVO2，外源碳源的ADP水平按以下顺序逐渐降低：葡萄糖、葡萄糖+胰岛素、棕榈酸酯+葡萄糖、乳酸、丙酮酸+葡萄糖和辛酸+葡萄糖。在辛酸和丙酮酸组中，MVO2（-1）与[ADP]-1呈线性相关，表观Km值在先前在分离线粒体中观察到的范围内。在MVO2与[Pi]的关系中也观察到了类似趋势。目前的研究结果表明，导致线粒体内NADH生成失调的外源碳源会将胞质ADP和Pi降低到限制氧化磷酸化速率的水平。对于其他碳源，控制NADH生成速率的过程也参与决定氧化ATP合成的速率。然而，如本数据和先前对分离线粒体和完整心肌中ATP合成过程的动力学研究所表明的，这种控制必须通过动力学方式而非近平衡热力学机制来实现[La Noue, K. F., 等人（1986年）《生物化学》25卷，7667 - 7675页；Kingsley - Hickman, P., 等人（1987年）《生物化学》26卷，7501 - 7510页]。
