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¹⁴CO₂ Fixation, Glutamate Labeling, and the Krebs Cycle in Ribose-grown Hydrogenomonas facilis

^a Department of Chemistry, Washington State University, Pullman, Washington

ABSTRACT

Exposure of ribose-grown Hydrogenomonas facilis to ¹⁴CO₂ for 6 to 12 sec during ribose oxidation resulted in labeling of a number of compounds, three of which were glutamate, phosphoglycerate, and pyruvate. Phosphoglycerate and pyruvate were labeled almost exclusively in C₁, suggesting operation of the reductive pentose phosphate cycle. Glutamate was labeled initially to the extent of 90% in C₁ and 10% in C₅, and this was followed by a concentration of radioisotope in C₅. All of the enzymes of the tricarboxylic acid cycle were detectable in ribose-grown cells, and, in general, specific activities were similar to those found in yeast extract-grown cells. Reduced nicotinamide adenine dinucleotide oxidase, aconitase, and the dehydrogenases for pyruvate, -ketoglutarate, and succinate appeared to be of particulate origin. In addition to enzymes of the tricarboxylic acid cycle, an acetyl coenzyme A-stimulated phosphoenolpyruvate carboxylase was found, as was isocitrate lyase. Possible participation of these catalysts in glutamate synthesis is discussed.

¹ Research Career Development Awardee (1-K3-AI-5,268) of the U.S. Public Health Service.

² NASA Trainee.

³ Predoctoral Fellow (GPM-16,383) of U.S. Public Health Service. Present address: Concordia College, Moorhead, Minn.