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Beyond the Chemiosmotic Theory: Analysis of Key Fundamental Aspects of Energy Coupling in Oxidative Phosphorylation in the Light

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Beyond the Chemiosmotic Theory: Analysis of Key Fundamental Aspects of Energy Coupling in Oxidative Phosphorylation in the Light J Bioenerg Biomembr (2010) 42:293–300 DOI 10.1007/s10863-010-9296-5 Beyond the Chemiosmotic Theory: Analysis of Key Fundamental Aspects of Energy Coupling in Oxidative Phosphorylation in the Light of a Torsional Mechanism of Energy Transduction and ATP Synthesis— Invited Review Part 1 Sunil Nath Received: 3 December 2009 /Accepted: 3 April 2010 /Published online: 20 May 2010 # Springer Science+Business Media, LLC 2010 Abstract In Part 1 of this invited article, we consider the Coupling . Membrane and ion transport . Electrogenic . fundamental aspects of energy coupling in oxidative Electroneutral . Valinomycin . Uncoupler . Unified theory of phosphorylation. The central concepts of the chemiosmotic ATP synthesis and hydrolysis theory are re-examined and the major problems with its experimental verification are analyzed and reassessed from first principles. Several of its assumptions and interpreta- Introduction tions (with regard, for instance, to consideration of the membrane as an inert barrier, the occurrence of energy The fundamental process of oxidative phosphorylation in transduction at thermodynamic equilibrium, the completely mitochondria constitutes the core of bioenergetics. The delocalized nature of the protonmotive force, and the notion quest for a comprehensive understanding of the link of indirect coupling) are shown to be questionable. between energy-generating and energy-utilizing processes Important biological implications of this analysis for in the cell has inspired an immense amount of research. Yet molecular mechanisms of biological energy transduction a complete understanding of the subtle and complex are enumerated. A fresh molecular mechanism of the problems in biological energy coupling and the detailed uncoupling of oxidative phosphorylation by classical weak elucidation of the molecular mechanism of the functioning acid anion uncouplers and an adequate explanation for the of the F1FO-ATP synthase and their counterpart elements in existence of uncoupler-resistant mutants (which until now photosynthetic energy transduction and photophosphoryla- has remained a mystery) has been proposed based on novel tion have defied even the intense research efforts of insights arising from a new torsional mechanism of energy numerous individuals and groups (Lipmann 1941; Davies transduction and ATP synthesis. and Krebs 1952; Slater 1953; Pullman et al. 1960; Williams 1961; Mitchell 1961;Williams1962; the group of Keywords Bioenergetics . F1FO-ATP synthase . Oxidative Lehninger (Lehninger 1964;Reynafarjeetal.1982); Phosphorylation . Photosynthesis and Mitchell 1966; Chance and Mela 1966; Pressman et al. photophosphorylation . Mitochondria . Energy 1967; Morowitz 1978; Kell 1979; Williams 1979; Green transduction . Chemiosmotic theory. Torsional mechanism . 1981; the group of Slayman (Hansen et al. 1981); Slater 1987; Boyer 1993; the group of Walker (Stock et al. 1999; S. Nath (*) Menz et al. 2001); Senior et al. 2002; the group of Pedersen Department of Biochemical Engineering and Biotechnology, (Bianchet et al. 1998; Chen et al. 2004); Junge et al. 2009). Indian Institute of Technology, Delhi, In the 1970s, after considerable debate and controversy, Hauz Khas, the chemiosmotic theory emerged as the mechanism New Delhi 110016, India “ ” e-mail: [email protected] generally accepted ( more by erosion of the opposition, e-mail: [email protected] in the words of Prebble (2002)). Williams, however, 294 J Bioenerg Biomembr (2010) 42:293–300 launched vigorous opposition to the theory, which he The central physiological-cum-biochemical coupling contended was based on false premises and postulated concept of chemiosmosis more localized models of coupling (Williams 1961; Williams 1962; Williams 1979). He independently devel- According to the chemiosmotic theory, the flux of electrons oped the idea that respiratory chains produce protons by through the electron transport chain leads to the generation charge separation and that these protons are coupled to of a delocalized electrical potential (Δ8) by uncompensat- phosphorylation (Williams 1961; Williams 1962). He ed, electrogenic translocation of protons from one bulk ascribed the coupling to anhydrous protons localized within aqueous phase to the other across the energy-transducing the hydrophobic matrix of the membrane, i.e., in his membrane (Mitchell 1961; Mitchell 1966). This general mechanism, the protons responsible for ATP synthesis principle, called “coupling by proticity”, was hypothesized are intramembrane and are delivered to the F1FO-ATP to energize bulk aqueous media on either side, such that synthase without crossing the coupling membrane. Com- this “protonmotive power” couldbeusedbyother prehensive critiques of the chemiosmotic theory were also complexes inserted in the membrane, such as F1FO-ATP published by others (Green 1981; Slater 1987). Therefore, synthase (Mitchell 1979). This protonmotive force, Δp, it must be stressed that the acceptance of the chemios- was expressed in electrical potential units (mV) by the motic theory was by no means universal, and currently a equation considerable amount of experimental data is found to be Δp ¼ Δ8 À 2:303RT ΔpH=F ð1Þ incompatible with the theory (Nath 2003). Indeed there are a large number of new mechanistic issues and where R is the universal gas constant, T the absolute searching questions that have not been answered satisfac- temperature and F the value of Faraday’s constant. torily by chemiosmosis nor by any of the other older In mitochondria, the major part of the Δp was presumed mechanisms and theories. to correspond to a delocalized electrical potential across the During the past 15 years, the current author has inner mitochondrial membrane. The protonmotive force formulated and developed in detail an alternative approach was postulated to be maintained because of the low that has become known as the torsional mechanism of permeability of the inner mitochondrial membrane to ions. energy transduction and ATP synthesis (Nath 1994; Nath The membrane itself was conceived by chemiosmosis to act 1997; Nath 1998; Rohatgi et al. 1998; Nath et al. 1999; simply as an “insulator” between the energized aqueous Nath et al. 2000; Nath and Jain 2000; Jain and Nath 2000; media on either side and not to participate in conforma- Jain and Nath 2001; Nath and Jain 2002; Nath 2002; Nath tional changes or energy transduction. Further, in the 2003; Jain et al. 2004; Nath 2004; Nath 2006; Nath 2008; theory, uncouplers of oxidative phosphorylation were Nath and Nath 2009). The original proposal and its logical thought to act as proton conductors that achieve their development has been shown to resolve the fundamental uncoupling action by dissipating the protonmotive gradient issues in biological energy transduction discussed above but do not interact specifically with components of the ATP and has offered new ways of analyzing and interpreting the synthase. plethora of experimental data. Recently, using a novel Thus a major tenet of the theory is that the sum of the systems biology/engineering approach, the rationale has interchangeable Δ8 and ΔpH components across bulk been advanced as a powerful unifying concept in bioener- aqueous phases generated in mitochondria by oxidation- getics and motility through the formulation in detail of the reduction reactions provide an adequate Δp (Eq. 1) and act unified theory of ATP synthesis and hydrolysis (Nath 2004; as the sole driving force of phosphorylation, i.e. through Nath 2006; Nath 2008; Nath and Nath 2009). indirect coupling mediated by Δ8 or Δp. Several reports On the tenth anniversary of the realization of the torsional have appeared in the literature that the putative driving mechanism (Nath et al. 1999), we propose, in Part 1 of this force, Δp, is inadequate in magnitude to perform this role invited review, to summarize the central concepts of (Slater et al. 1973; Deutsch et al. 1979) and that ATP chemiosmosis and discuss major problems with its experi- synthesis occurs at physiological rates in several biological mental verification. These have been analyzed and reas- systems at low values of Δp (Ferguson and Sorgato 1982; sessed from first principles to identify their important Westerhoff et al. 1984; Slater 1987; Tupper and Tedeschi biological implications. A fresh molecular mechanism of 1969). The original proponents of the theory have the action of the classical anionic uncouplers of oxidative addressed this key issue only once (Mitchell and Moyle phosphorylation has been proposed based on novel insights 1969), even though this is of fundamental importance and arising from the torsional mechanism and the unified theory. has major implications for molecular mechanisms of Since the article deals with the very topics epitomized by the biological energy transduction. Their cryptic calculations, title of this journal, we expect that it would be of great reported in a single Table, have not been seriously tested or relevance and interest to the readers of the journal. derived from first principles. Do the calculations and the J Bioenerg Biomembr (2010) 42:293–300 295 interpretations resulting from them withstand careful inside versus outside measures 340 and a concentration of a scrutiny? species in the outer compartment has to be multiplied by this factor to obtain its correct concentration in the inner compartment. Problems with the experimental verification The above analysis gives the concentration factor of chemiosmosis and reassessment of the results required
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