The enzyme, characterized from the bacteria?Escherichia coli?and?Bacillus subtilis, is involved in the recycling of the murein peptide, of which?L-Ala-D-Glu is a component.?In vitro?the enzyme from?E.coli?epimerizes several?L-Ala-L-X dipeptides with broader specificity than the enzyme from?B.subtilis. Formerly EC?5.1.1.n1.