Aromatic Amino Acids Absorb Light in the Near-Ultraviolet

Aromatic Amino Acids Absorb Light in the Near-Ultraviolet 

The aromatic amino acids phenylalanine, tyrosine, and tryptophan all possess absorption maxima in the near-ultraviolet (fig. 3.7). These absorption bands arise from the interaction of radiation with electrons in the aromatic rings. The near- 

Titration curve of /3-lactoglobulin. At very low values of pH ( 2) all ionizable groups are protonated. At a pH of about 7.2 (indicated by horizontal bar) 51 groups (mostly the glutamic and aspartic amino acids and some of the histidines) have lost their protons. At pH 12 most of the remaining ionizable groups (mostly lysine and arginine amino acids and some histidines) have lost their protons as well. 

Ultraviolet absorption spectra of tryptophan (Trp), tyrosine (Tyr), and phenylalanine (Phe) at pH 6. The molar absorptivity is reflected in the extinction coefficient, with the concentration of the absorbing species expressed in moles per liter. (Source From D. B. Wetlaufer, Adv. Protein Chem. 17 303-390, 1962.) 

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Amino Acids Have Both Acid and Base Properties Aromatic Amino Acids Absorb Light in the Near-Ultraviolet... 

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