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Electrochemical potential of ions have been postulated to play a major role in free energy transductions and information transfer of cells. In neural transmission, Na and K currents are responsible for the generation and propagation of the action potential [1,2]. In mitochondrial ATP synthesis, the proton gradient across the inner membrane is the high energy intermediate, which, upon translocation of protons along the electrochemical gradient, transfers its potential energy to ATPase for the synthesis of ATP [3-8]. In photosynthetic processes, the energy of a photon is used to pump a proton into an energy reservoir and ATP synthase then uses the electrochemical potential energy of the proton for synthesis of ATP [7,9,10]. Notwithstanding, there is no compelling evidence which would exclude a direct energy transfer between the electric field and a protein, thus allowing a temporary storage of energy in the conformational states of the protein [11]. Previously, we proposed a mechanism, Electroconformational Coupling (ECC), to test the feasibility of direct energy transaction between a transmembrane electric field and an enzyme conformational equilibrium for driving ion pumps and ATP synthesis [12-15]. Here we will summarize new experimental evidence and analysis based on the concept of ECC. We will examine and compare the ECC model and the common enzyme catalytic process as exemplified by the Michaelis-Menten Mechanism. The electric potential across cell membranes is of the order of 10 to 250 mV, which corresponds to a field intensity of 20 to 500 kV/cm. Under such a strong field, molecules will behave quite differently than they will under the zero field condition. Ion pairs will dissociate, dipoles will orient, molecules will be electronically and automatically polarized, equilibria between different conformers of a protein will be shifted, etc. [16,17]. There are two geometric situations under which these changes can take place. The first is where all molecules and ions freely diffuse. The second is when they are fixed relative to the field direction. The first situation is represented by a reaction in an homogeneous aqueous solution. The field effect on the rapidly tumbling molecule is generally small and has been discussed elsewhere [12,16,17]. Here we will focus on the second situation which is more relevant for dealing with effects of an electric field on a membrane protein. Let us start by considering a general enzyme catalytic reaction. |
