A model of mitochondrial energy coupling has been proposed based on the principles of paired charge separation and vectorial paired charge flow. The unique role of the electron transfer chain and ionophores in mediating charge separation is emphasized.The present model evolved in three stages. The study of configurational transitions in isolated mitochondria led to the concept of a conformationally strained energized state (1) generated by an exergonic center and discharged by an endergonic center (the conformational model). The study of energized proton ejection in turn led to the concept of the energized state as a charge-separated state (2, 3) with the protein acting as an electromechanochemical transducer (the electromechanochemical model). Finally, the study of respiratory control in liposomal vesicles of cytochrome oxidase (4) led to the recognition of the primary role of moving charges in energy coupling. From the conformational model, the principle of direct coupling between exergonic and endergonic centers was deduced. From the electromechanochemical model was derived the principle that energy coupling requires the charge-separated state in both exergonic and endergonic centers. Thus, the two earlier models prepared the ground for the development of the moving charge model (5, 6). THE PAIR MOVING CHARGE MODELExergonic and Endergonic Centers. Coupling invariably involves two reaction centers vectorially aligned with respect to the membrane (see Fig. 1)-one in which an exergonic reaction (the driving reaction) takes place and the other in which endergonic reaction (the driven reaction) takes place. The two centers are separated by a linkage system to be defined later which facilitates the coupling of the two respective chemical reactions. We are assuming complete separation in space of the exergonic and endergonic centers and no mixing of any of the reactants or products.The exergonic and endergonic reactions proceed in a vectorial fashion (see Fig. 2) so that the initial reactants are on one side of the membrane and the final products are on the other side of the membrane (7)(8)(9).The Essentiality of the Charge-Separated State for Energy Coupling. Chemical energy may be defined as the energy intrinsic to the system of paired electrons and protons in atoms and molecules. The utilization of chemical energy requires, as a first preliminary, the tearing out of charges beyond orbital constraints. We are thus postulating that the charge-separated state of the reactants in a chemical reaction is a prerequisite for energy coupling.Consider the energy of an electron and a proton in a H atom (the valency state) and the energy of the separated electron and proton at a critical distance at which orbital interactions no longer apply. We are assuming that this separation is achieved by the appropriate conditions (paired charge separation) and with the necessary catalysts, e.g., an electron transfer chain or an ionophore, to satisfy the requirements for reversibility. According to Kemeny (10), the valency stat...
The thesis is developed that an acceptable model of biological energy coupling must have universal application. The paired moving charge model of mitochondrial energy coupling is examined from the standpoint of this thesis. Fundamental to this model is the notion that energy coupling involves interaction between paired uncompensated charged species in two vectorially aligned and spatially separated reaction centers. The two charge-separating devices are assumed to be the electron transfer chain (in chloroplast and mitochondria) and intrinsic ionophores (in all transducing organelles and kinases). The universality of the ionophore principle becomes then the crucial test of the validity of the paired moving charge model. The multiple facets of ionophoremediated coupled processes are explored, e.g., coupled hydrolysis of ATP, hormonal control of ion movements, and active transport.The design and performance of living systems reflect to a profound degree two sets of principles-the principles of heredity and the principles of energy. The double helix principle of nucleic acid construction enunciated by Watson and Crick two decades ago (1) has been shown by overwhelming evidence to apply across the board to the hereditary process in all types of cells and in all forms of life. Moreover, all the events and systems that translate the hereditary process reflect with great fidelity both the centrality and the uniqueness of the double helix principle. The systems that execute replication (ribosomes, messenger RNA, transfer RNA, chromosomes, and the mitotic apparatus) and that control replication (genes, cistrons, and operons) are in fact molecular devices for the precise translation of the double helix principle. The point to be made is that, given a universal principle of heredity, then all the agents, systems, and tactics that underlie the execution of this principle must also be universal in nature. The ribosome and transfer RNA are two such examples in the structural domain. The mechanisms of protein and nucleic acid synthesis are examples in the functional domain. The universality of the genetic code is an example in the domain of molecular strategy.We have considered elsewhere the compelling nature of the case for the proposition that the principles of energy, like those of heredity, must be universal in character in biological systems (2, 3). We shall restrict our treatment of energy to the molecular tactics by which two processes are coupled one to another. Energy coupling subtends the most crucial aspects of energy in biological systems, and in our view, the understanding of all other aspects of energy, such as catalysis, is derivative from the fundamental principles of energy coupling. In the previous communication of this series, we have proposed and developed a model for mitochondrial energy coupling (4). Since the principles that underlie the model were arrived at by the fitting of theory and experiment, the ability of the model to rationalize mitochondrial energy coupling is in large measure a reflect...
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