Photochemical Addition of Amino Acids and Peptides to Polyuridylic Acid

The quantum yields for photochemical addition of glycine and the L‐amino acids commonly occurring in proteins (excluding proline) to polyuridylic acid have been determined in deoxygenated phosphate buffer at pH 7, using a fluorescamine assay technique. All twenty amino acids were found to be reactive, with cysteine, tryptophan, phenylalanine, tyrosine, arginine, lysine and methionine being the most reactive. The analogous quantum yields for a series of eighteen dipeptides of the form glycyl X (X being one of the commonly occurring amino acids, including proline), of L‐alanyl‐L‐tryptophan, of the tripeptides L‐seryl‐L‐seryl‐L‐serine and L‐threonyl‐L‐threonyl‐L‐threonine, of the tetrapeptide L‐cystine‐bis‐glycine, and of the lysine derivative Nα‐acetyllysine were also measured. All were found to be reactive toward photoaddition to poly U.