Comparative toxicity of some naturally occurring and synthetic non-protein amino acids

Evaluation of the comparative toxicity of 55 non-protein amino acids, in terms of their effect on growth of Lemna minor, revealed that these compounds possess a wide diversity in their growth-inhibiting ability. Replacement of the sulphur atom by selenium in protein amino acids and certain fluoro-substitution was toxic. Addition of a methyl or phenyl group to the carbon skeleton of an individual protein amino acid did not affect Lemna growth. The tested amino acids were arranged in order of their decreasing toxicity and, for convenience, were divided into five groups based on their relative toxicity. Group I included the most disruptive secondary amino acids and members of Group II and III exhibited an intermediate growth inhibiting capacity. Slightly toxic secondary amino acids and compounds which had no discernible effect on Lemna growth were placed in Group IV and V, respectively.