Succinic dehydrogenase of Azotobacter vinelandii.

During the investigation of the Krebs cycle in Azotobacter agile, strain 4.4 (Repaske and Wilson, 1953), it was found that whole cells normally required 20 minutes before adaptation to succinate, but succinoxidase activity could be demonstrated in cell-free extracts made from unadapted cells. If extracts prepared in a 10 kc Raytheon sonic oscillator were centrifuged at 145,000 G for 30 minutes, the supernatant fluid still retained its ability to oxidize all members of the tricarboxylic acid cycle. Succinic dehydrogenase and the terminal electron transport sytem, both usually associated with particulate cell material, were present in the supernatant fluid. As preparations from Azotoacter vinelandii, strain 0, had similar properties, the enzyme from this organism was studied because the cells could be stored at -10 C for at least 5 months without loss of enzyme activity, and total units of enzyme per gram of cells was greater than in A. agile preparations although the specific activity was no higher.