The Effect of Inhibitors on Succinoxidase*

In a previous publication it was shown that succinic acid is rapidly oxidized by homogenized suspensions of chick kidney (1). In view of the fact that succinic acid is an important intermediate in tissue oxidat.ions (2-4) it seemed desirable to study some of the properties of the succinoxidase system by means of the new technique. Quastel and Woolridge (5), using the methylene blue technique, showed that toluene-treated Bacillus coli were able to oxidize succinic acid as easily as did the untreated organisms, although the treated organisms were inactive with respect to many other substrates. They demonstrated the fact that malonic acid markedly inhibits the oxidation of succinic acid. Later Quastel and Wheatley (6) included minced rabbit muscle and brain, and human brain in their studies, using the Barcroft technique. They used 0.5 gm. of minced tissue in a total volume of 3 cc. In the case of the animal tissues, malonic acid again inhibited the oxidation of succinic acid. Clutterbuck (7) studied the conversion of succinic acid and fumaric acid into Lmalic acid by a polarimetric method. He showed that 30 gm. of minced liver in a volume of about 500 cc. could convert 5 gm. of succinic acid to an equilibrium mixture of fumaric and malic acids (about 3.5 gm.) in 6 hours, while the conversion of fumaric acid required only 2 hours. It thus appears that both fumarase and succinoxidase were highly active at the dilution employed in his experiments, and that the fumarase reaction is the faster of the two. Ogston and Green (8) have