Origin, Microbiology, Nutrition, and Pharmacology of D‐Amino Acids

Abstract

Exposure of food proteins to certain processing conditions induces two major chemical changes: racemization of all L-amino acids (LAAs) to D-amino acids (DAAs) and concurrent formation of cross-linked amino acids such as lysinoalanine (LAL). The diet contains both processing-induced and naturally-formed DAA. The latter include those found in microorganisms, plants, and marine invertebrates. Racemization impairs digestibility and nutritional quality. Racemization of LAA residues to their D-isomers in food and other proteins is pH-, time-, and temperature-dependent. Although racemization rates of LAA residues in a protein vary, relative rates in different proteins are similar. The nutritional utilization of different DAAs varies widely in animals and humans. Some DAAs may exert both adverse and beneficial biological effects. Thus, although D-Phe is utilized as a nutritional source of L-Phe, high concentrations of D-Tyr in such diets inhibit the growth of mice. Both D-Ser and LAL induce histological changes in the rat kidney. The wide variation in the utilization of DAAs is illustrated by the fact that, whereas D-Meth is largely utilized as a nutritional source of the L-isomer, D-Lys is not. Similarly, although L-CysSH has a sparing effect on L-Meth when fed to mice, D-CysSH does not. Since DAAs are consumed as part of their normal diet, a need exists to develop a better understanding of their roles in foods, microbiology, nutrition, and medicine. To contribute to this effort, this overview surveys our present knowledge of the chemistry, nutrition, safety, microbiology, and pharmacology of DAAs. Also covered are the origin and distribution of DAAs in food and possible roles of DAAs in human physiology, aging, and the etiology and therapy of human diseases.

A novel pathway for the production of hydrogen sulfide from D-cysteine in mammalian cells

“…Discussion L-Amino acids are nonenzymatically racemized by heat and alkaline conditions applied during food processing, and 21-44% of L-cysteine is changed to D-cysteine by alkaline treatment 28,29 . D-cysteine may thus be mostly provided from food.…”

Amino Acid Racemization in Pseudomonas putida KT2440

“…Nonetheless, the D-enantiomer of each of the 19 amino acids is detected in biological systems (1)(2)(3)(4)(5)(6), and in certain environments, D-amino acids are abundant. These include microbe-rich environments, such as topsoil (7), fermented foods (8), and the rumen (9). Where free D-amino acid content is measured in bacterial culture supernatants or ethanolic extracts of freeze-dried bacterial samples, the most abundant free D-amino acid is typically D-alanine, but high concentrations of D-aspartate, D-glutamate, D-leucine, and D-methionine are also noted in some species (1,9).…”

Five primary sources of organic aerosols in the urban atmosphere of Belgrade (Serbia)

“…In the atmosphere, Gly suggests a more aged aerosol (Samy et al, 2013) correlated to long-range transport (Barbaro et al, 2011;Samy et al, 2013). D-AAs are used as markers of bacterial material both in terrestrial and marine environments (bacterioplankton) (Friedman, 2010;Kaiser and Benner, 2008;McCarthy et al, 1998). Enantiomeric D/L ratios are used as indicators of bacterial origin.…”