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Title:   Author  item
                                            Friedman, Mendel
  Submitted to: Chemistry and Biodiversity
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 1/1/2010
                                    Publication  Date: 6/16/2010
                                    Citation: Friedman, M. 2010. Origin, Microbiology, Nutrition, and Pharmacology of D-Amino Acids. Chemistry and Biodiversity. 7(6):1491-1530Interpretive Summary: We previously declined an invitation to participate in the First International Conference of D-Amino Acid Research, Awaji Island, Japan, July 1-4, 2009. However, in response from the invitation of one of the organizers (Professor Hans Brueckner, Research Centre for BioSystems, Land Use, and Nutrition, Giessen University, Germany), we agreed to contribute a review paper to the Proceedings which will be published in the peer-reviewed journal Chemistry & Biodiversity. Exposure of food proteins to certain processing conditions induces two major chemical changes: racemization of all L-amino acids (LAA) to D-amino acids (DAA) and concurrent formation of crosslinked 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 L-amino acids residues to their D-isomers in food and other proteins is pH-, time-, and temperature-dependent. Although racemization rates of L-amino acid residues in a protein vary, relative rates in different proteins are similar.  The nutritional utilization of different DAA varies widely in animals and humans. Since DAA 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 DAA. Also covered are the evolutionary origin of chirality, distribution of DAA in food and possible roles in aging, and the causes and therapy of human diseases.  It is worth noting that microbes are a major source of dietary DAA, that that cell walls of both Gram-positive and Gram-negative bacteria consist of DAA-containing peptidoglycans, that DAA-containing natural peptide antibiotics (bacitracin, gramicidin) possess strong antimicrobial properties, and that peptides may acquire antibiotic competence upon racemization.
                                Technical Abstract: Exposure of food proteins to certain processing conditions induces two major chemical changes: racemization of all L-amino acids (LAA) to D-amino acids (DAA) and concurrent formation of crosslinked 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 L-amino acids residues to their D-isomers in food and other proteins is pH-, time-, and temperature-dependent. Although racemization rates of L-amino acid residues in a protein vary, relative rates in different proteins are similar. The nutritional utilization of different DAA varies widely in animals and humans.  Some DAA 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 DAA 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 DAA 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 DAA. Also covered are the origin and distribution of DAA in food and possible roles of DAA in human physiology, aging, and the etiology and therapy of human diseases.


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