Utilization of carbon dioxide in the synthesis of proteins by Escherichia coli. II.

The question of the mechanisms involved in protein synthesis is one of the most important problems in biology. One facet that has recently become amenable to experimental approach is the process of synthesis or accumulation of constituent amino acids. In an earlier paper (1) we have reported the utilization of Cl402 in protein synthesis by Escherichia coli and the identification of labeled aspartic and glutamic acids, arginine, lysine, proline, and threonine. Isotopic carbon was found in the amidine and carboxyl carbons of arginine, cr-carboxyl carbon of glutamic acid, and in the &carbon of aspartic acid. In the present paper additional information concerning the biochemical pathways involved in the synthesis of these six amino acids is presented. In experiments described below, the basal media possessing glucose as the sole energy source, and glucose and labeled carbon dioxide as the carbon sources, were supplemented with the six above amino acids and other additives. Thus the bacteria were presented with a choice between synthesis of their requirements for aspartic and glutamic acids, arginine, lysine, proline, or threonine and utilization of the preformed amino acids. The effect of some possible intermediate compounds in synthesis of these amino acids was similarly examined. The Cl4 content of the proteins was found to vary with the concentration and species of the additive employed. The results of these experiments have given new information on the relationships among the pathways of amino acid synthesis.