, AND H. R. HOMANN. Characteristics and intermediates of short-term C'402 incorporation during ribose oxidation by Hydrogenomonas facilis. J. Bacteriol. 89:839-847. 1965.-Ribose-grown cells of Hydrogenomonas facilis, which had been suspended in growth medium and were oxidizing ribose, were exposed to HC'403of high specific activity. The uptake was proportional to cell mass. Short-term uptake (less than 2 min) was completely inhibited by 10-3 M 2,4-dinitrophenol (DNP) or by <4 X 10-6 M m-chlorocarbonyl cyanide phenylhydrazone, and to the extent of 42% by 5 X 10-5 M DNP. The following observations were made in kinetic studies (8, 16, 35, 67, 96, and 181 sec) of fixation in the presence of ribose. Glutamate was extensively labeled in periods up to 3 min. It was one of the major early products, containing 30% of the label at 8 sec. The sugar phosphate fraction was not detectably labeled at 8 or 16 sec, but its C14-content increased rapidly to 27%o at 35 sec and then slowly decreased. Label in phosphoglycerate, phosphoenolpyruvate, and alanine did not appear until 35 sec, and did not exceed about 7, 2, and 3%, respectively, of the total extracted radioactivity. Adenosine triphosphate and adenosine diphosphate were heavily labeled after fixation in a pilot study for 125 sec. Although considerable radioactivity incorporated during the pilot study was intractable by the extraction procedure employed, virtually no C14 was found in the residue in poly-,B-hydroxybutyric acid. A large number of amino acids and organic acids and some organic phosphates were not detectably labeled in any of the experiments. Omission of ribose greatly diminished incorporation, particularly into glutamate.
MCFADDEN, BRUCE A. (Washington State University, Pullman), AND H. ROBERT HOMANN. Quantitative studies of the effect of organic substrates and 2, 4-dinitrophenol on heterotrophic carbon dioxide fixation in Hydrogenomcnas facilis. J. Bacteriol. 86:971-977. 1963.-Whole cells of Hydrogenomonas facilis under heterotrophic conditions fixed levels of C1402 which depended upon the nature of the carbon source being oxidized. It was established that oxidative rates varied as a function of PCO2. Therefore, all studies were conducted in the presence of 1.5 mole % CO2 in the gas phase. With glucosegrown cells supplied with glucose as substrate, the heterotrophic fixation was curtailed 98% by
Exposure of ribose-grown Hydrogenomonas facilis to '4CO2 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 C,, suggesting operation of the reductive pentose phosphate cycle. Glutamate was labeled initially to the extent of 90% in C, and 10% in C(, 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, a-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.
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