Question?

The following is data on the four aromatic amino acids. If these are all aromatic, why are histidine and phenylalanine left off of Figure 3-6 in your book?

Phenylalanine has a molar extinction coefficient of 195 M^-1cm^-1 at 257.5 nm [G. D. Fasman, Handbook of Biochemistry and Molecular Biology, Proteins, I, 183-203, CRC Press, 3 ed., 1976].

Histidine has a molar extinction coefficient of 5,700 M^-1cm^-1 at 211 nm [G. D. Fasman, Handbook of Biochemistry and Molecular Biology, Proteins, I, 183-203, CRC Press, 3 ed., 1976].

Tryptophan has a molar extinction coefficient of 5,579 M^-1cm^-1 at 278 nm [G. D. Fasman, Handbook of Biochemistry and Molecular Biology, Proteins, I, 183-203, CRC Press, 3 ed., 1976].

Tyrosine has a molar extinction coefficient of 1,405 M^-1cm^-1 at 274.25 nm [G. D. Fasman, Handbook of Biochemistry and Molecular Biology, Proteins, I, 183-203, CRC Press, 3 ed., 1976].