The α and β subunits of hemoglobin bear a remarkable structural similarity to myoglobin. however, for hemoglobin subunits, residues that are hydrophilic in myoglobin are hydrophobic. why?

The hemoglobin and myoglobin are structurally similar, but myoglobin is a monomer, while a hemoglobin molecule is a tetramer. The hydrophobic subunits of the hemoglobin molecule take part in the van der wall interactions with the subunits of others via the similar regions. This shields them from the aqueous surroundings. Therefore, the residues which are hydrophilic in the structurally similar myoglobin are hydrophobic in hemoglobin.