Kinetics of formation and utilization of metabolic pools in the biosynthesis of protein and nucleic acid

Abstract

A study of the kinetics of formation and utilization of metabolic pools of amino acids and phosphorus in T. utilis has been carried out using 14C-fructose and 32PO 4 ---. The distribution of these tracers among the chemical fractions of the cell during steady-state conditions was first established. The interrelationships among these fractions in the formation of metabolic pools and in the transfer of pool material for protein and nucleic acid synthesis were then determined. The pools were demonstrated to be complex and so the kinetics of formation and transfer of individual pool amino acids were investigated. These investigations and a study of the effects of wxogenous amino acid competitors upon pool amino acids led us to the following conclusions. 1. 1. The carbon of the cold TCA-soluble fraction is mostly contained in amino acids and acts as a metabolic pool for the synthesis of protein and nucleic acid. The TCA-soluble fraction also contains a metabolic pool of phosphorus which supplies phosphorus for nucleic acid and other end products found in the hot TCA-soluble fraction. 2. 2. The results of kinetic investigations permit the distinction between endogenous metabolic pools as essential intermediates for synthesis and reservoir pools not on the main line of synthetic events. The amino acid and phosphorus pools are in the direct line of synthetic events converting exogenous substrate to endogenous macromolecular compounds. 3. 3. The pool amino acids are not free amino acids but are adsorbed to larger molecules and these adsorption sites are intimately connected with the process of protein synthesis. 4. 4. Internal conversion of one pool amino acid to another pool amino acid may occur on a single site prior to incorporation into protein. 5. 5. Nucleic acids are probably not the macromolecules furnishing the adsorption sites since there are more than 3 times as many pool amino acids as there are nucleotides. The protein fraction is the only cellular component present in sufficiently large quantities to furnish the adsorption sites for the pool amino acids. A mixture of nucleic acid and protein is not excluded however.