Site of synthesis of the peptide component of the cell wall of Bacillus megaterium

Abstract

In the presence of growth-inhibitory concentrations of chlor-amphenicol, the incorporation of most L-[C14] amino acids into the protein fractions of B. megaterium is inhibited about 96%. Incorporation of L-[C14] alanine into the cellular protein is only 50-85% inhibited by the same concentration of chloramphenicol. The residual incorporation can be accounted for largely by the uptake of C14 into the peptide fraction of the cell wall. However, when the L-[C14] alanine is presented to the cell for less than 2 min., the proteins of the membrane fraction are more highly labelled than are the cell-wall peptides. In the presence of growth-inhibitory concentrations of both penicillin and chloramphenicol, L-[C14] alanine is incorporated into the protein of the cytoplasmic-membrane fraction, but not appreciably into the cytoplasmic protein or the cell-wall peptides. In the presence of chloramphenicol, L-[C14]-aspartic acid is still converted relatively efficiently into the protein or peptide fractions of the cell-wall and cytoplasmic membrane. Radio-autographs of these fractions show that the radioactivity is mainly associated with diaminopimelic acid. It is concluded that the peptide components of the cell wall are synthesized at sites on or closely associated with the cytoplasmic membrane.