The assimilation of amino acids by bacteria. 18. The incorporation of glutamic acid into the protein fraction of Staphylococcus aureus

Abstract

When washed suspensions of Staphylococcus aureus are incubated with glucose and C14-labelled glutamic acid (condition 1), the protein fraction of the cells becomes progressively more radioactive. The radioactivity is associated with the glutamic acid residues of the protein. The rate of this glutamic acid incorporation is increased by the addition of a mixture of amino acids containing all those essential for growth (condition 2). Omission of certain essential amino acids, such as histidine or tryptophan, results in the rate of incorporation falling to that obtained in condition 1. Omission of aspartic acid results in a greatly increased rate of incorporation which lasts for 30-60 min. and then falls to that under condition 1. The incorporation is abolished if the reaction temp. rises to 60[degree] or over. Incorporation under condition 1 is markedly less sensitive to inhibition by chloramphenicol or Aureomycin, and markedly more sensitive to inhibition by penicillin or bacitracin, than incorporation under condition 2. The incorporation of glutamic acid into cell protein under condition 1 is accompanied by a decrease in the specific activity but not the total amt. of the free glutamic acid within the cells. Inhibition of incorporation by penicillin or bacitracin does not affect the total amt. of free glutamic acid within the cells, but prevents the decrease in its specific activity. The processes involved in the incorporation of a variety of radioactive amino acids show differing sensitivities to penicillin, bacitracin, and chloramphenicol. The process most sensitive to penicillin is that involved in the incorporation of glutamic acid.