Synthesis of C4-dicarboxylic acids from pyruvate by Hydrogenomonas eutropha strain H 16

1. Crude extracts and partially purified enzyme preparations obtained from Hydrogenomonas eutropha strain H 16 have been tested for enzymes carboxylating pyruvate and phosphoenolpyruvate. Radiometric methods employing 14C-bicarbonate have been used for the determination of enzyme activities; due to the presence of high activities of NADH oxidase coupled optical tests were unsatisfactory. 2. The rates of carbon dioxide fixation are dependent on the growth substrate of the cells (fructose, lactate, succinate, and hydrogen + carbon dioxide). 3. The activities of phosphoenolpyruvate carboxykinase and phosphoenolpyruvate carboxylase are high. By acetyl coenzyme A the latter enzyme was stimulated by a factor of four or five. 4. The presence of a biotin dependent pyruvate carboxylase could be excluded, while under the same experimental conditions this enzyme could be determined in yeast. 5. The results are discussed with respect to similar investigations in other autotrophic microorganisms