Distribution of amino acids in the cellular fractions ofStaphylococcus aureus

WhenStaphylococcus aureus cells were labeled with a single radioactive amino acid for 20 minutes, the highest activity, except for alanine, leucine, and glycine, was found in the free pool. Significant amounts of the above amino acids and also valine and methionine were incorporated into the protein — cell wall fraction.Cells previously labeled with a single amino acid underwent a net loss of radioactivity when transferred to buffer, glucose, or complete medium. An exception was glycine. The greatest loss in activity occurred in the free pool.While some amino acids (alanine, cystine) were transferred from the free pool to the protein — cell wall fraction under all conditions tested, others (glutamic acid, proline) were transferred only under conditions of growth.Cells labeled with certain single amino acids and then transferred to a complete medium lost a significant portion of the label. The most extreme case noted was proline, but other amino acids also effluxed from the cell under these conditions.