Is tyrosine hydrophobic or hydrophilic?
The answer to this question emerges from an examination of the structure of tyrosine — or, more strictly, the tyrosyl residue, which is how it exists in proteins, the concern of the question:


  It has both hydrophobic and hydrophilic features and can exhibit both
  behaviours depending on the circumstances.


The ring is aromatic and hydrophobic, but the hydroxyl substituent is hydrophilic.

It is important not to try to fit things into rigid classifications that may not be appropriate for them. Indeed, one should ask how useful a particular classification is in any circumstance, and be aware of its limitations.

The classic illustration of the importance of these dual properties of tyrosine is in Perutz’s description of the differences between the oxy- and deoxy- structures of haemoglobin, where oxygenation of the haem cause the movement of tyrosine from the hydrophobic interior of the protein to the hydrophilic surface. This movement is associated with breaking of ionic bonds between the subunits in the overall change in quaternary structure:



(This is a modified version of Fig. 3 of the original, produced many years ago for teaching purposes. The wiggly line is a cartoon representation of the polypeptide chain of the α-subunit of haemoglobin between His-F8 and the C-terminal Arg residue. For clarity, the preceding region is not shown but its continuation indicated by an arrow head.)