The Specificity for Amino Compounds

The ability of the water-soluble DD-carboxypeptidases of Streptomyces strains albus G, R61, Kll and R39 to perform transpeptidation was studied. The donor was diacetylL-lysyl-D-alanyl-D-alanine, and a whole range of amino acids, peptides and structurally related amino compounds were tested for acceptor function. No compound tested was an acceptor for the enzyme from strain albus G whereas the enzymes from strains R61 and Ki1 could utilize with varying efficiency a wide range of substances including peptides with N-terminal glycine or D-alanine, co-amino acids, aminohexuronic acids, 6-aminopenicillanic acid and D-cycloserine. Certain peptides, when present in higher concentration, inhibited the transpeptidation observed at lower concentration. The enzyme from strain R39 would not use any dipeptide as an acceptor, but a few compounds that were not glycine or a-amino acids of the D-configuration did function thus. These were D-cycloserine and the lactams of mesoor racemic-diaminoadipic acid.