D-Amino acid

"Environmental ᴅ-amino acids are thought to be derived from organic diagenesis such as racemization and release from bacterial cell walls and even from microbial production.

[3] An immense amount of D-Ser can also be detected in the brain, wherein it composes a significant regulatory role in the development of the "central nervous system and is closely associated with learning, memory, and mammalian behavior."

A great amount of D-Ser, has also been "detected in human urine; it plays a regulatory role in pathogenic gene expression in the urinary system.

Aside from those two special cases, L- and D-amino acids have identical properties (color, solubility, melting point) under many conditions.

Even though D-amino acids are minimal constituents of living organisms, they occur in a broad range of natural environments such as soils, rivers, lakes, marine systems, snow and ice, aerosols and precipitation.

They have been known to synthesize more than 10 kinds of D-amino acids, most frequently D-alanine and D-glutamate for crosslinking within the peptidoglycan cell wall.

Apart from structural function in the bacterial cell wall, D-amino acids have also been associated to growth fitness and to further processes such as biofilm development, spore germination and signaling.

Amino-acid racemase, a PLP-dependent enzyme, racemizes amino acids via the formation of the alpha-iminoacids, where the stereogenic center is lost.

The D-alanine in peptidoglycans that comprise bacterial cell walls helps its host resist attack by proteolytic enzymes.

In another study, from 56 sediments collected from the deep sea (depth range 800–1500 m), "28 ᴅ-amino acid utilizers" were isolated, in Sagami Bay, Japan.

Most conducted studies and experiments usually also utilize mainly D-alanine, D-aspartate, and D-glutamate, as they signify the most common D-amino acids found in living organisms.