Biochemistry of Amino Acids - A. Majster 1961

General Biochemistry and Physiology of Amino Acid Metabolism
Racemization of Amino Acids
General Remarks

D-Amino Acids were first obtained in 1886 by Schulze and Bosshard, who utilized The phenomenon of stereospecific assimilation of racemic amino acids by the mold Penicillium glaucum (p. 80). D-Amino acids were discovered in natural sources considerably later. To date, A number of D-Amino acids have been identified in Materials of biological origin (p. 67). It has been established that some of these compounds can undergo enzymatic transformations, and research is currently underway to elucidate THE ORIGIN OF D-Amino Acids and their metabolic pathways.

Certain D-amino acids, when incorporated into the diet in place of their corresponding L-isomers, can support animal growth and microbial reproduction. In most cases, these D-isomers are apparently converted into L-amino acids via Oxidative Deamination to form α-keto acids, followed by re-amination through Transamination. It should be emphasized that this mechanism of D-amino acid inversion in the Organism cannot be considered fully proven; nevertheless, these concepts are consistent with data indicating that animal and Microbial growth can be supported by α-keto analogues of Certain amino acids, as well as with the existence and widespread distribution of D-Amino Acid Oxidase and various transaminases. Observations on the growth of young rats have demonstrated that the corresponding α-keto derivatives can be administered to the organism instead of the D-amino acids that replace the respective L-amino acids. At the same time, in some instances α-keto acids (for example, the α-keto analogues of leucine and isoleucine) support the growth of young animals, whereas their corresponding D-Amino acids are not utilized by the growing organism; these findings suggest that The rate of oxidative deamination of D-amino acids is not always high enough to sustain animal growth.