D/L Amino Acids

Optical isomers can have very different biological properties. They can interact with enzymes in a different way such as one isomer is bioactive, and the other is not. In other case, one isomer is associated with a different outcome or pathway from the other. Optical isomers can also have a different taste profile. D and L amino acids do not always present the same taste.  Aside from endogenous optical isomers, bacteria and cancer cells can produce and utilize D and L amino acids in different ways. While L-Histidine (the common isomer) is bitter, D-Histidine is sweet. While L-Glutamate (the common isomer) is Umami (think MSG), the D-isomer of glutamate is sour. All living systems are made up of L-amino acids, which is the biologically active form found in proteins, peptides and utilized by cells for cellular metabolism. However, D-amino acids can also be present in certain disease states, as well as, in normal metabolism.  D amino acids have been observed in brain tissue from Alzheimer’s patients and in patients’ plasma with kidney disease. Scientists have also linked D-amino acids to other diseases, including cancer and schizophrenia. This is a largely unexplored area such that the majority of metabolomics platforms do not differentiate these isomers.