A study of succinoxidase system in rat liver mitochondria has been made, with special reference to the site of action of ethylurethane, and the site of electron transfer to several electron acceptors in this system.
1. The inhibitory action of ethylurethane on succinoxidase system varied with the variety of acceptors used and it was not observed when brilliant cresyl blue was the acceptor. The inhibition was completely reversible up to the concentration of 0.5 M.
2. The existence of two pathways: an “antimycin A-sensitive” and an “antimycin A-resistant, ” was indicated to link ferricyanide, 2, 6-dichlorophenolindophenol, and methylene blue with the succinoxidase system. One of the factors involved in the antimycin A-sensitive pathway is cytochrome c.
3. The sensitivity of succinoxidase toward ethylurethane was exaggerated by the treatment with antimycin A and BAL and by the addition of cytochrome c. On the other hand, simultaneous addition of ethylurethane failed to protect the inhibition by BAL. Antimycin A titer of succinoxidase was decreased slightly by the presence of ethylurethane.
4. From these results, the mechanism of action of ethylurethane was discussed together with that of antimycin A and BAL, and it was concluded that the site of action of ethylurethane lies at the portion of cytochrome b and Slater factor.
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