The effects of dietary amino acid levels upon lysine and methionine requirements for growing rats.

The amino acid requirement has been investigated by many laboratories since 1931. Authors considered that the requirement was influenced by the protein level of the basal diet and also by the experimental method. In light of those earlier studies, the present study investigated the effect on lysine and methionine requirements by modifying total nitrogen level or essential amino acid level. The result of our study confirmed that when the amino acid requirement for maximum growth was expressed as the dietary percentage, amino acid to total amino acid ratio, and amino acid to total nitrogen ratio, the requirement had changed according to not only essential amino acids but also to nonessential amino acids. Furthermore, we investigated the relationship between amino acid intake and body protein gain, and found that 6.2 mg lysine and 9.0 mg methionine were required for the maintenance of a rat weighing 80 g and 71.6 mg of lysine and 48.8 mg of methionine were required for one gram of body protein gain. The lysine and methionine intakes required for one gram of protein gain were equivalent to 100% and 124% of amino acid contents of body protein, respectively.