A fuel cell model in biological energy conversion

Consideration of the high energy conversion efficiency of biological systems leads to the idea that mechanical energy may arise via a series of steps, of which a rate-determining one occurs in a fuel-cell-like element. The mitochondrion is suggested as the site of such entities. The observed efficiency would be consistent with a potential loss of about 0.5 V. The supposed biological fuel cells would be able to act as an electrical power source, driving chemical reactions against their spontaneous direction. Considerations of electrical conductance in wet proteins shows that ohmic (i.e., non-interfacial) potential differences through mitochondrial membranes could be negligible. The cathodic reaction would be the reduction of oxygen, O₂+4H⁺+4e^-→H₂O and the anodic reaction, 2NADH⁺→2NAD+2H⁺+4e^-. The anodes are suggested as being molecular, buried in the invaginations of the inner membrane forming the cristae. The cathodes are located on enzymes which are probably on the inner side of the membrane but could be, respectively, on the outer (cathodic), and the inner (anodic) sides. The electron transport occurs though proteins within each membrane. The relation of the so-called fuel cell potentials to potentially observable membrane potentials, and those measured by fluorescent probes, are discussed. The fuel cells produce electrical energy and this energy is transferred to ADP by an electrolytic route, using electric power from the cells to work the endergonic ATP synthesis. Possible electrode reactions are suggested. An exponential dependence of the rate of ATP synthesis upon applied potential has been observed. Biological cells radiate electromagnetically in the 10⁹ to 10¹⁵ Hz region. Such phenomena support a fuel cell model of a biological cell because they demand the presence of mobile electrons.