Incorporation of S-[3H]methyl-d-cysteine into the peptidoglycan of ether-treated cells ofEscherichia coli

Abstract

Certain d-amino acids can be incorporated into the murein sacculus of Escherichia coli apparently through a direct transpeptidation reaction independent of the normal biosynthetic pathway. Investigation of this process is important because it could lead to the identification of hitherto unknown enzymes involved in murein metabolism. However, a serious drawback is the lack of an appropriate in vitro assay. We have analysed the suitability of a system based on the incorporation of a radioactive substrate (S-[3H]methyl-d-cysteine) by ether-treated cells, a method successfully applied before to the study of murein biosynthesis. The results reported here indicate that ether-treated cells are indeed proficient in the incorporation of d-amino acids, matching closely the properties of the reaction in growing cells.