FURTHER STUDIES ON THE REDUCTION OF TRIPHENYLTETRAZOLIUM CHLORIDE BY THE SUCCINIC DEHYDROGENASE COMPLEX

Pigeon breast muscle succinoxidase purified by repeated isoelectric precipitation, could not reduce TTC in the presence of succinate even though the excess amount of boiled extract of liver or crude coenzyme A as cofactor was added. And TTC reducing activity was restored by the addition of dialyzed supernatant of rat liver homogenate.<br>It was concluded that a certain protein component, which is contained in rat liver supernatant and has no succinic dehydrogenase activity by itself, was required for TTC reduction by succinoxidase with cofactor.<br>Rat liver particles could not efficiently reduce TTC in the presence of succinate, but the addition of boiled supernatant and dialyzed supernatant could restore the TTC reducing activity. The addition of each one, per se, could not restore the activity.<br>The system for the determination of cofactor activity was suggested because the amount of boiled extract or crude coenzyme A became a rate limiting factor under the addition of the excess amount of dialyzed rat liver supernatant.<br>Rat liver homogenate could reduce TTC in the presence of reduced cytochrome c. In this case, also, the cofactor and protein component were required for efficient TTC reduction by rat liver particles.<br>Methylene blue could enhance the TTC reduction in rat liver homogenate by succinate. Cyanide strongly inhibited TTC reduction in rat liver homogenate by succinate, but inhibited it less in the addition of methylene blue.<br>From these results, the mechanism of TTC reduction by succinoxidase were discussed.