•Substitutions:
As Tyrosine is an aromatic, partially hydrophobic, amino acid, it prefers substitution with other amino
acids of the same type (see above). It
particularly prefers to exchange with Phenylalanine,
which differs only in that it lacks the hydroxyl group in the ortho position on the benzene ring.
•Role in function: Unlike the very similar Phenylalanine, Tyrosine contains a reactive hydroxyl group, thus making it much
more likely to be involved in
interactions with non protein atoms.
Like other aromatic amino acids,
Tyrosine can be involved in interactions with non-protein ligands that themselves contain aromatic
groups via stacking interactions.
•A common role for Tyrosines (and Serines and Threonines)
within intracellular proteins is
phosphorylation. Protein kinases frequently attach phosphates to Tyrosines in order to fascilitate
the signal transduction process. Note that in
this context, Tyrosine will rarely substitute for
Serine or Threonine, since the enzymes that catalyse the reactions (i.e. the protein kinases) are highly specific
(i.e. Tyrosine kinases generally do not
work on Serines/Threonines and vice versa)