RESPIRATORY ENZYMES IN OXIDATIVE PHOSPHORYLATION

Abstract

The cytochromes of the non-phosphorylating DPNH’ and succinate oxidase preparations (1, 2) have been examined in detail by visual (1) and photoelectric (3) spectroscopic methods, and it is often tacitly assumed that the oxidative phosphorylation system of mitochondria contains an identical set of respiratory enzymes that act in the same way as those in non-phosphorylating preparations (4). In order to determine the properties of intact mitochondria, we have studied by direct spectrophotometric methods the respiratory enzymes of rat and guinea pig liver preparations. Our method allows us to observe the spectra of the components of the respiratory chain with as little mutual interference as possible because the spectrophotometer is used differentially to respond only to small changes of absorption caused by the effect of specific reactants upon the enzyme system (5). The properties of the mitochondrial respiratory chain are rather different from those of non-phosphorylating preparations, especially with respect to pyridine nucleotide, flavoprotein, and cytochrome c. In addition to cytochromes a3, a, and b, which are present in about the usual relationship, cytochrome e, cytochrome bg, and catalase are identified spectroscopically in the mitochondrial preparations by suitable chemical tests. The components of the mitochondrial respiratory chain, determined by their difference spectra, represent those readily observed to participate in electron transfer in intact yeast or ascites tumor cells (6-8). On the basis of spectroscopic data given here and kinetic data given later (9), we find that no abbreviated respiratory chain is involved in the phosphorylating DPNH oxidase system; cytochrome b, (2, 4) and flavoprotein (10) are present and functioning, as are cytochromes c, a, and a3 (ll), in spite of reports based upon non-phosphorylating systems.