Paired Moving Charges in Mitochondrial Energy Coupling

The postulate of charge pairing in the mitochondrial inner membrane is justified by applying a formula due to Fuoss to calculate the probability density for the distance between a positive and a negative charge. For dielectric constants 10 or less pairing is absolute, for 20 there is some tendency towards pairing, and at 78 it is nonexistent. Pairing, partner exchange or charge substitution, inhibition, and antiport uncoupling can be rationalized within this framework.In the charge pair model presently under development (1)(2)(3)(4)(5) the pairing of opposite charges is the fundamental principle by which the operation of mitochondria and of other bioenergetic systems is rationalized. This pairing has so far been treated as a postulate. Due to its fundamental significance it needs to be justified and its limitations must be explored.The distribution of all charges in and near the mitochondrial inner membrane is a problem of discouraging complexity unless some simplifying principle is recognized. The experimental techniques available in the field tend to focuson the electrons in the electron transfer chain. This point of view does not seem to lead to a successful theory. It was necessary to recognize that energy passes between two charges (6, 7), and that these charges are of-opposite sign (1). One of them can be the electron. Classification of charge separationsThere are two fields which have historically dealt with the distribution of charges from the point of view of our present interests. One is physical chemistry, as exemplified by the theory of catalysis (8), which deals with charge separations of the order of 1 A. The other one is the theory of electrolytes (9), which is valid for distances between charges larger than a few Angstroms, so that specifically quantum mechanical effects can be ignored. The medium here is characterized by a dielectric constant, which of course also means charge separation, but on a scale usually much smaller than 1 A. The charge separations of primary bioenergetic interest fall into the range of competence of the theory of electrolytes.The separation of ions in electrolytic solutions was investigated by Fuoss (9, 10). If one positions a negative ion at the center of coordinates, the probability density G(r) of finding the nearest positive ion between distances r and r + dr is G(r) = 47rr2p exp -47rp f x2e~/xdx}, In an electrolytic solution charges of both signs are free to move in three-dimensional space. The only restrictions arise from the mutual electrostatic interaction of the ions themselves and their distance of nearest approach a in Eq. [1]. This means that there is a competition between the energetic effect of the attractive Coulomb interaction favoring the nearest possible approach of opposite charges and the entropy effect favoring separations of the order of p -" due to the larger configurational volume available at larger separations. Low values of the dielectric constant make the Coulomb interaction dominant and charges tend to pair. High values of the dielec...

Section: Classification Of Charge Separationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

See 1 more Smart Citation

Physical basis of charge pairing in mitochondria.

Kemény¹,

Singer²

1975

“…This cavity we assume to be the space between the unattached portions of the ETC and ITC complexes, a separating distance of only 15 A being sufficiently small to allow strong charge-charge interaction during paired charge separation (1).…”

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confidence: 99%

Resolution of complex III of the mitochondrial electron transfer chain into two component complexes.

Fry¹,

Green²

1978

Corplex III can be resolved into an electron transfer complex an an ion transfer complex. The electron transfer complex contains exclusively the oxidation-reduction proteins of complex III, and the ion transfer complex the capability for augmenting cation-induced fluorescence of 8-ani-lino-l-naphthalenesulfonic acid. This finding has important implications for the molecular mechanism of mitochondrial energy coupling. The middle segment of the mitochondrial respiratory chain involved in the catalytic reduction of cytochrome c by reduced coenzyme Q and containing cytochromes b and cl is designated complex III (bcl-complex).The principle of paired charge separation (1) leads to the prediction that energy coupling systems should be resolvable into an exergonic and an endergonic center (2). The present communication documents evidence on the resolution of complex III into an electron transfer complex (ETC) and an ion transfer complex (ITC).EXPERIMENTAL PROCEDURES Preparation of Complex III. The method of Rieske (3) was used. It was found that freezing the dialysate overnight led to a more complete precipitation of the S-1 fraction (4), and this procedure was therefore routinely employed. Final preparations of complex III were dissolved in 0.01 M Tris-HCI (pH 7.4) to about 30 mg of protein/ml and dialyzed against 100 vol of the same buffer for 4-6 hr at 4VC. Sufficient cholate and ammonium sulfate were removed by this step so that the point of insolubility of complex III was just reached.Assay of Complex III. Catalytic activity of complex III was estimated by measuring the reduction of cytochrome c at 550 nm as adapted from the method of Green and Burkhard (5) by Rieske (3) with reduced coenzyme Q2 as reductant.Estimation of Protein. The biuret method after bleaching of heme by hydrogen peroxide (6) was used routinely to determine protein with bovine serum albumin as standard. Where necessary, protein samples were first solubilized with deoxycholate and/or alkali.Estimation of Heme. The pyridine hemochromogen method of Basford et al. (7) was routinely used for the determination of ci and b heme. Spectral measurements were made in a Cary model 118 spectrophotometer. The mM absorption coefficients used were as follows: cytochrome b (reduced pyridine hemochromogen at 558 nm) 34.7 and cytochrome cl (reduced minus oxidized pyridine hemochromogen at 550 nm) 19.1.The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.

“…Ionophores occupy a central position in energy coupling systems by virtue of their unique capability for charge separation (1,2). The present communication has two objectives-first, to summarize the rapidly growing body of experimental evidence relevant to the intrinsic ionophores of the mitochondrion, and second, to provide a framework and perspective for the new field of experimental inquiry revolving about these intrinsic ionophores.…”

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Paired moving charge model of energy coupling. III. Intrinsic ionophores in energy coupling systems.

Green¹,

Blondin²,

Kessler³

et al. 1975

The experimental basis for the postulated role of intrinsic ionophores in mitochondrial ion transport and energy coupling is summarized. Intrinsic ionophores appear to be linked to, or contained within, specific ionophoroproteins localized in the inner membrane, and the isolation of these ionophores requires their release from the ionophoroproteins. At least ten different species of ionophores have been isolated from the mitochondrion, five of which have been wholly or in part chemically identified. Intrinsic ionophores have been implicated in the activation of inorganic phosphate in ATP synthesis and hydrolysis, and in the control of the coupling modes. The presence of ionophores in soluble proteins such as troponin and in ATP-energized kinases has been demonstrated.Ionophores occupy a central position in energy coupling systems by virtue of their unique capability for charge separation (1, 2). The present communication has two objectives-first, to summarize the rapidly growing body of experimental evidence relevant to the intrinsic ionophores of the mitochondrion, and second, to provide a framework and perspective for the new field of experimental inquiry revolving about these intrinsic ionophores.Historical. The use of antibiotic ionophores in the study of energy coupling in mitochondria has a long history dating back to the discovery by Dubos and Hotchkiss (3) that the polypeptide antibiotics produced by Bacillus brevis, collectively referred to as gramicidin, were uncouplers of mitochondrial oxidative phosphorylation (4, 5) and facilitated the movement of K+ across bacterial membranes (6). Lardy (7,8) and Pressman (9, 10) have been the pioneers in examining the modulating role of antibiotic ionophores on mitochondrial energy coupling and in introducing the use of antibiotic ionophores for the study of energy coupling. Eisenman (11,12) and Eigen (13) have developed the framework of principles which underlie the transport of ions across membranes by antibiotic ionophores. In recent years, ionophoretic activity has been demonstrated in a wide variety of molecular structures (14); moreover, the synthetic chemist has shown great aptitude in designing molecular structures that exhibit ionophoretic capability (14).The curious point is that, although these experimental and theoretical developments established beyond peradventure that ionophores were active at incredibly high dilutions in facilitating ion transport, and provided the perfect models for the natural mediators of active transport and ion movements generally, nonetheless there was great reluctance, nay strong opposition, to taking the next obvious step of identifying the natural mediators of ion movements as ionophores. What was the basis for this resistance to the next obvious step? There were three main reasons. First, since extrinsic ionophores were antibiotics and potentially lethal reagents, the presence of natural counterparts of these ionophores in coupling systems was deemed to be highly improbable. Second, the concept of fixed channels i...