Extraction of 2,4,6-trinitrophenyl derivatives of amino acids and peptides from aqueous acid. A simple method for determining aminotripeptidase activity

2,4,6-Trinitrophenyl (TNP) amino acids and peptides vary greatly in the extent to which they are extracted from acid solution into organic solvents. A method based on this observation is described, in which leu is determined specifically in the presence of gly-gly and an excess of leu-gly-gly. This method has been applied to the assay of aminotripeptidase activity in some tissue extracts, using leu-gly-gly as substrate. Extraction characteristics of many TNP-amino acids and -peptides are recorded. No solvent tested extracted all TNP-amino acids quantitatively from acid solution. The application of this information to the solution of other analytical problems is discussed.