Nutritional Value of d-Amino Acids, d-Peptides, and Amino Acid Derivatives in Mice

This paper describes a method for determining the nutritional value of
d-amino acids,
d-peptides, and amino acid derivatives using a growth assay in mice fed a synthetic all-amino acid diet. A large number of experiments were carried out in which a molar equivalent of the test compound replaced a nutritionally essential amino acid such as
l-lysine (
l-Lys),
l-methionine (
l-Met),
l-phenylalanine (
l-Phe), and
l-tryptophan (
l-Trp) as well as the semi-essential amino acids
l-cysteine (
l -Cys) and
l -tyrosine (
l -Tyr). The results show wide-ranging variations in the biological utilization of test substances. The method is generally applicable to the determination of the biological utilization and safety of any amino acid derivative as a potential nutritional source of the corresponding
l -amino acid. Because the organism is forced to use the
d -amino acid or amino acid derivative as the sole source of the essential or semi-essential amino acid being replaced, and because a free amino acid diet allows better control of composition, the use of all-amino acid for such determinations may be preferable to protein-based diets.