Urinary peptides; method for assay.

THE USUAL METHOD of peptide estimation requires the assay of a protein-free filtrate for amino-acid concentration before and after hydrolysis. Peptide amino acid is then calculated by difference (1). In another method (2) specifically designed for urine, the peptides are precipitated with phosphotungstic acid from a trichloroacetic acid filtrate. The precipitate is dissolved and color is formed by a reaction with Folin’s phenol reagent. A separate assay of uric acid must be made since this substance also reacts with the color-forming reagent. The method proposed in this paper is based on the reaction of a biuret reagent with the peptides of a protein-free filtrate of urine. The principal advantage of this method is its simplicity, which allows for fewer reagents and manipulations than either of the above methods and permits an assay to be completed within 1 hour.