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 tluorescamine 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 1.-cystine-bis-glycine, and of the lysine derivative N"-acetyllysine were also measured. All were found to be reactive toward photoaddition to poly U.

The photochemical quantum yields for addition of glycine and the L-amino acids commonly occurring in proteins (excluding proline) to polyadenylic acid, polycytidylic acid, polyguanylic acid and polyribothymidylic acid have been determined in deoxygenated phosphate buffer at A 254 nm and pH 7, using a fluorescamine assay technique. Polyadenylic acid was reactive with eleven of the twenty amino acids tested, with phenylalanine, tyrosine, glutamine, lysine and asparagine having the highest quantum yields. Polyguanylic acid reacted with sixteen amino acids; phenylalanine, arginine, cysteine, tyrosine, and lysine displayed the largest quantum yields. Polycytidylic acid showed reactivity with fifteen amino acids with lysine, phenylalanine, cysteine, tyrosine and arginine having the greatest quantum yields. Polyribothymidylic acid, reactive with fifteen of nineteen amino acids surveyed, showed the highest quantum yields for cysteine, phenylalanine, tyrosine, lysine and asparagine. None of the polynucleotides were reactive with aspartic acid or glutamic acid.The quantum yields for photoaddition of eighteen dipeptides of the form glycyl X (X being one of the amino acids commonly occurring in proteins, including proline), and of L-alanyl-L-tryptophan, L-seryl-L-seryl-L-serine, L-threonyl-L-threonyl-L-threonine, L-cystine-bis-glycine. and N"-acetyllysine to polyadenylic acid, polycytidylic acid and polyguanylic acid were measured. All of these were found to add photochemically to each of these polymers. Polyribothymidylic acid, tested with eleven of these peptides and with N"-acetyllysine, was found to be reactive with all.