The spectrophotometric determination of tyrosine and tryptophan in proteins

I8olation of veratric acid. Some 800 oothecae of Blatta orientali8 were crushed in dilute aqueous potassium cyanide (c. 250 ml.) containing some sulphur. dioxide. After 3 hr. the mixture was filtered with the aid of 'Hyflo supercel'. The filtrate was weakly acid-to litmus. The residue was extracted further by allowing to stand for 2 hr. with water (300 ml.) which had been made just acid to Congo red with sulphuric, acid, and the procedure repeated until the extracts no longer gave a green colour with ferHic chloride. The com- bined filtrate and extracts were concentrated in vacuo under nitrogen to small bulk (c. 300 ml.), the concentrate filtered from a trace of solid material and extracted continuously with peroxide-free ether (700 ml.). The ethereal extract which con- tained all the material giving a coloration with ferric chloride was concentrated to one-third bulk and treated with ethereal diazomethane (from 10 g. nitroso-N-methylurea). After 2 days the ether was evaporated and the residue refluxed for 2 hr. with methanolic potassium hydroxide' (2 %).