Studies on succinic dehydrogenase. I. Preparation and assay of the soluble dehydrogenase.

The investigations reported here evolved from studies on a coupled aerobic reaction between cysteinesulfinic acid (CSA)’ and a substance obtained from yeast extracts, which was catalyzed by soluble preparations from Proteus vulgaris and a variety of animal tissue, and yielded equal amounts of aspartate, pyruvate, and sulfate as products (2, 3). The reaction required DPN and an autoxidizable dye. Methylene blue, brilliant cresyl blue, and phenazine methosulfate served as carriers with bacterial extracts and homogenates of liver mitochondrial acetone powder, but only phenazine methosulfate was effective with heart preparations or with soluble enzyme extracts of liver mitochondria. No reduction of pyridine nucleotide occurred under anaerobic conditions and no cysteic acid was formed in the reaction, in contrast to CSA dehydrogenase action in bacteria (4). CSA alone was not oxidized, and the cosubstrate from yeast was only slowly oxidized in the absence of CSA. With the aid of a suitable assay system (3) the substance from yeast was isolated in pure form, and it was identified as succinic acid (2, 3). The over-all reaction could, then, be written as follows.