The Biology Project > Biochemistry > The Chemistry of Amino Acids
Tyrosine Y (Tyr)
Chemical Properties:
Aromatic
(Aromatic group & Hydroxyl group)Physical Properties:
Nonpolar
Tyrosine, an essential amino acid, is also an aromatic amino acid and is derived from phenylalanine by hydroxylation in the para position. While tyrosine is hydrophobic, it is significantly more soluble that is phenylalanine. The phenolic hydroxyl of tyrosine is significantly more acidic than are the aliphatic hydroxyls of either serine or threonine, having a pKa of about 9.8 in polypeptides. As with all ionizable groups, the precise pKa will depend to a major degree upon the environment within the protein. Tyrosines that are on the surface of a protein will generally have a lower pKa than those that are buried within a protein; ionization yielding the phenolate anion would be exceedingly unstable in the hydrophobic interior of a protein.Tyrosine absorbs ultraviolet radiation and contributes to the absorbance spectra of proteins. The absorbance spectrum of tyrosine will be shown later; the extinction of tyrosine is only about 1/5 that of tryptophan at 280 nm, which is the primary contributor to the UV absorbance of proteins depending upon the number of residues of each in the protein.
The Biology Project > Biochemistry > The Chemistry of Amino Acids
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