Abstract
The second derivative spectra of N-acetyl ethyl esters of tryptophan, tyrosine and phenylalanine were measured with various values of derivative wavelength difference, Δλ, at pH 7 and 13. The second derivative spectra of tryptophan at pH 7 and 13 were very similar at and Δλ, as were those of phenylalanine. However, the derivative spectrum of tyrosine at pH 13 was quite different from that at pH 7 ; at pH 7 there were two peaks and troughs between 270 and 300nm, whereas at pH 13, these spectral bands were not present but there were broad positive and negative spectral bands, due to acid dissociation of the phenolic-OH group. A method for the quantitative determination of these amino acids was developed on the basis of the spectral properties of the three aromatic amino acids. This method should be suitable for determining the amounts of these three aromatic amino acid residues in proteins.
