Un concepto unificado de transducción de energia por los sistemas bioquímicos

Abstract

Electronic energy —resulting either from electron excitation or localization — is the obligatory link between the different forms of energy (light, redox, acid-base, metahosphate-ortophosphate) transducible by biochemical systems. The key in energy coupling between any two transducing systems lies precisely in the fact that both of them share a common intermediate that cyclically participates in the overall transduction process by alternating between its electronically energized state and its unenergized basal state. All the energy-transducing biochemical systems must operate, according to their nature and character of the energization, at two midpoint redox potentials, at two pKa's, or at two phosphate transfer potentials. Three basic energy-transducing systems in bioenergetics, namely, redox, acid-base and metaphosphate- ortophosphate, couple between them through the acylium cation [R-C=0]**— carboxylate anion (R—COO") pair. These forms are, respectively, twice-energized and unenergized and can accept, at two energy levels, either two electrons or two protons or the ortophosphate anion (H2PO4") and the "zwitterion" metaphosphate (~PÕ3"**). Both at the substrate level and at the membrane level, ortophosphate energization to metaphosphate, by removal of an oxide anion (02~), brings about a decrease in pKa with the concomitant dissociation of the two protons (2Ht ) , whereas deenergization of metaphosphate to ortophosphate, by addition of an oxide anion, brings about an increase in pKa with the concomitant fixation of two protons. One of the greatest discoveries of bioenergetics was the introduction in cell metabolism of the one-electron redox photosystem chlorophyll a and was followed by the starting of the one-electron/one-proton redox/acid-base energytransducing systems of the photosynthetic and respiratory electron transport chains.