Aromatic amino acids primarily absorb light at a wavelength of 280 nm.
This absorption is due to the presence of aromatic rings in their structures. Specifically, the aromatic amino acids responsible for this UV absorption are:
- Tyrosine: Contains a phenol group.
- Tryptophan: Contains an indole ring system.
- Phenylalanine: While it also has an aromatic ring, its absorption at 280 nm is significantly weaker compared to tyrosine and tryptophan. Consequently, phenylalanine contributes minimally to the overall UV absorption of proteins at 280 nm.
Because proteins often contain tyrosine and tryptophan, their concentration can be estimated by measuring their absorbance at 280 nm using spectrophotometry. This is a common and convenient method in biochemistry and molecular biology. The Beer-Lambert Law can then be applied to quantify the protein concentration.
