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An aromatic amino acid (AAA) is an amino acid that includes an aromatic ring. Among the 20 standard amino acids, the following are aromatic: phenylalanine, tryptophan and tyrosine. However, in addition to being aromatic, tyrosine can be classified as a polar amino acid. In addition, while histidine contains an aromatic ring, its basic properties cause it to be predominantly classified as a polar amino acid; however, the compound is still aromatic. Aromatic amino acids absorb ultraviolet light at a wavelength above 250 nm and produce fluorescence. This characteristic is used in quantitative analysis, notably in determining the concentrations of these amino acids in solution. This achieved through the utilization of a UV spectrophotomer and the Beer-Lambert Law equation. Most proteins will have an absorption maximum at 280 nm due to the presence of aromatic amino acids in their primary structure. However, because several aromatic amino acids exist, this method has low accuracy; in order to mitigate this issue, the desired protein must be pure, and its molar absorptivity is known. In addition, a protein without aromatic amino acids will not have an absorption maximum at approximately 280 nm. The presence of nucleic acids in the protein can further decrease the method's accuracy due to the presence of purine and pyrimidine rings, which have an absorption maximum at approximately 260 nm. Phenylalanine has a relatively weak absorbance in comparison to the other standard aromatic amino acids; its presence in a protein can only be detected if tryptophan and tyrosine are not present. Its absorption maximum occurs at 257 nm. Consequently, it has a relatively weak fluorescence. Tryptophan has the highest relative absorbance in comparison to the other standard aromatic amino acids; its absorption maximum occurs at 280 nm. The side chain of tryptophan does not titrate. The absorption maximum of tyrosine occurs at 274 nm. In chemical reactions, tyrosine can function as a nucleophile. Aromatic amino acids also play a crucial role in glycan-protein interactions. #Geneics #aminoacids #aromaticAminoAcids #peptides
