Isolation and purification of D-alanyl-meso-2, 6-diaminopimelic acid endopeptidase of Streptomyces L-3 enzyme using soluble substrates of known chemical structure from Lactobacillus plantarum cell wall digests.

D-alanyl-meso-2, 6-diaminopimelic acid (D-Alanyl-meso-A2pm) endopeptidase was isolated and purified from a crude Streptomyces L-3 enzyme preparation by ion exchange chromatography and isoelectric focusing in a density gradient. During its purification, its hydrolytic activity was assayed on cell walls of Lactobacillus plantarum ATCC 8014 and soluble glycopeptides and peptides, of known chemical structures, prepared enzymatically from these cell walls. A fraction with an isoelectric point of pH 7.9 cleaved the bond between the carboxyl group of the D-alanine residue at the C-terminal in one peptide subunit and one of the two amino groups of the A2pm residue in the neighboring peptide subunit. Unlike the crude enzyme, the endopeptidase in this fraction showed no N-acetylmuramyl-L-alanine amidase, A2pm carboxyamide amidase or proteinase(s) activity and it was immunologically homogeneous.