The effect of rotenone on respiration and its point of attack.

The action of rotenone on the respiration of fish gill filaments from Leuciscus rutilus (L.), mouse liver slices, and rat liver mitochondria has been studied. 1. 1. Exposure of intact and excised gill filaments to rotenone induces an inhibition of their oxygen consumption. This effect was more pronounced when the gill filaments were brought into contact with the rotenone in vivo. 2. 2. Rotenone also induced a decrease of the oxygen uptake of mouse liver slices, but in order to obtain the same degree of inhibition in liver slices as in gill filaments, the concentration of rotenone had to be increased 50 times. 3. 3. In isolated rat liver mitochondria the aerobic oxidation of pyruvate was almost completely inhibited by 6.0 × 10−7 M rotenone, but in the same experiment this concentration had no effect on the oxidation of succinate. The inhibition of the oxidation of pyruvate induced by rotenone was decreased to 14 per cent by addition of methylene blue. 4. 4. Addition of methylene blue reduced the inhibition of the oxygen uptake of gill filaments caused by rotenone after excision, as well as in vivo. 5. 5. Uncoupling of the phosphorylation by 10−4 M DNP did not release the inhibition of mitochondrial respiration caused by rotenone. 6. 6. By investigating the difference spectra of the components of the respiratory chain in a mitochondrial suspension it was found that the diaphorase, cytochromes b, c, a, and a3 were oxidized in the presence of rotenone. 7. 7. These results indicate that rotenone blocks in the electron transporting system a link which is situated at the diaphorase level.