Incorporation of C 14 From Carbon Dioxide into Sugar Phosphates, Carboxylic Acids, and Amino Acids by Clostridium thermoaceticum

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Abstract
Ljungdahl, Lars (Western Reserve University, Cleveland, Ohio), and Harland G. Wood . Incorporation of C 14 from carbon dioxide into sugar phosphates, carboxylic acids, and amino acids by Clostridium thermoaceticum . J. Bacteriol. 89: 1055–1064. 1965.—The mechanism of synthesis of acetate from carbon dioxide by Clostridium thermoaceticum was investigated by incubating cells with glucose or xylose in the presence of C 14 O 2 . Sugar phosphates, amino acids, and carboxylic acids were isolated and the specific radioactivities were determined; the distributions of C 14 were also determined in some of the compounds. Only fructose-1,6-diphosphate, formate, and lactate had higher specific activities than the acetate. The specific activities and distribution of C 14 in the fructose-6-phosphate and ribose-5-phosphate were such that we conclude that the synthesis of acetate does not occur via a pathway involving the sugar phosphates as direct intermediates. Likewise, it is shown that pathways including lactate, aspartate, serine, glycine, malate, and succinate are not of importance in the synthesis of acetate from CO 2 . The methyl group of free methionine was unlabeled and is not a precursor of the methyl group of acetate.