Tetrachlorohydroquinone Oxidase Activity in Beef Heart Mitochondria

SUMMARY The properties of the oxidation of tetrachlorohydroquinone (THQ) by beef heart mitochondria are described. The addition of protamine is essential for enzymatic activity in mitochondria, although other mitochondrial preparations, such as electron transport particles, can catalyze the oxidation of THQ at maxi- mal rates in the absence of polycation. It is suggested that the addition of protamine to mitochondria which are in a partially open form converts them to a closed system similar to electron transport particles. Specificity studies show that only the tetrahalogenated hydro- quinones can serve as a substrate for the enzyme. Substances such as duroquinone are not enzymatically oxidized by mito- chondrial preparations. It is proposed that the addition of THQ to protamine results in a model cytochrome c compound in which the protein moiety is replaced by protamine, and the heme group by THQ. In mitochondrial preparations, it seems that the cytochrome c oxidase system is responsible for the oxidation of THQ. The effects of inhibitors and the rapid reduction of cytochromes a and u3 indicate that the primary site of interaction of THQ and the respiratory chain may be cytochrome a itself, or that the interaction is between cytochromes a and u3. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. REFERENCES