On the specificity of the uridine diphospho-N-acetylmuramyl-alanyl-D-glutamic acid: diamino acid ligase of Bifidobacterium globosum.

The peptidoglycan of Bifidobacterium globosum contains ornithine and lysine alternately in the same position of the peptide subunit. The uridine diphospho-N-acetylmuramyl-alanyl-D-glutamic acid: diamino acid ligase of this organism was purified 700-fold. Since the activities for the incorporation of ornithine and lysine into uridine diphospho-N-acetylmuramyl-tripeptide did not separate during purification and since the incorporation of ornithine is competitively inhibited by lysine and vice versa, both ornithine and lysine are assumed to be incorporated by one single enzyme. Studies on the specificity of the ligase toward analogs of ornithine have shown that the enzyme requires a diamino, monocarboxylic acid with 4-6 carbon atoms. Methylation of the epsilon-amino group or hydroxylation of the delta-carbon atom of lysine decreases the competitive properties of the analog, whereas the substitution of the gamma-methylen group by sulfur (S-2-aminoethyl cysteine) results in a highly competitive compound.