D-amino acid hydrolysing enzymes

Only a few enzymes that hydrolyse peptide bonds involving D-amino acids effectively have been discovered and characterised in multicellular organisms. Mammalian renal dipeptidase hydrolyses various dipeptides with a D-amino acid only at the C-terminal with similar efficiency to their L-amino acid diastereomers, but not dipeptides with an N-terminal D-amino acid residue. Nor does the enzyme act on tripeptides. Dipeptides similar to those hydrolysed by the enzyme are also hydrolysed by cytosolic leucine aminopeptidase, but much less effectively than their L-amino acid diastereomers. Peptidyl-D-amino acid hydrolase from cephalopods has a somewhat broader substrate specificity than the renal dipeptidase and hydrolyses, as well, some dipeptides with a D-amino acid at the N-terminal. It also acts on larger peptides than dipeptides, albeit slowly. Carnosinase is specific to dipeptides containing L-His as the C-terminal residue, and hydrolyses D-Ala-L-His about as well as carnosine.