The interaction of energy and electron transfer reactions in mitochondria. I. General properties and nature of the products of succinate-linked reduction of pyridine nucleotide.

Several observations stimulate interest in the quantitative aspects of energy expenditure in the reduction of pyridine nucleotide and the oxidation of cytochrome. First, a comparison of energy conserved in electron transfer with that expended in its reversal gives a measure of the efficiency of the process: the full energy of the oxidation-reduction reaction must be expended in activating the reverse of electron transfer, whereas the forward reaction may conserve only part of the free energy change involved. A second point of interest concerns a theory of active transport postulating a mechanism by which the energy stored in adenosine triphosphate can be used to activate electron transfer. Indeed, it is possible that the adenosine 5’-triphosphate-electron transfer activity demonstrated in our experiments is, in principle, that postulated for the active transport processes in gastric secretion (1). Third, these experiments may provide a model for cytochrome oxidation and pyridine nucleotide reduction observed upon illumination of anaerobic cells of photosynthetic organisms such as Rhodospirillum rubrum. This paper describes several approaches to a quantitative evaluation of the efficiency with which adenosine 5’-triphosphateelectron transfer reactions may proceed in the energy-linked reduction of pyridine nucleotide and oxidation of cytochrome. The experimental results show this to be a highly efficient process which may be compared with the over-all efficiency of oxidative phosphorylation.