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home / study / science / chemistry / questions and answers / myoglobin is a protein containing 153 amino acids. ... Question Myoglobin is a protein containing 153 amino acids. Approximately half of the amino acids in myoglobin have polar side chains. Where would you expect these amino acid side chains to be located in the tertiary structure of the protein? Where would you expect the nonpolar side chains to be? Would you expect myoglobin to be more or less soluble in water than a protein composed primarily of nonpolar amino acids? Why?

Explanation / Answer

Myoglobin, an extremely compact heme protein, found primarily in cardiac and red skeletal muscles, functions in the storage of oxygen and facilitates the transport of oxygen to the mitochondria for oxidative phosphorylation.

The inside and outside surfaces of the protein are well defined. The interior consists almost entirely of nonpolar residues including leucine, valine, methionine, and phenylalanine. Polar residues such as aspartate, glutamate, lysine, and arginine are absent from the interior protein surface. In fact, two histidines are the only polar residues which play an integral role in the binding of heme oxygen. The outside of the protein has both polar and nonpolar residues.

Since myoglobin has polar residues on the outside it will be more soluble in water compard to a protein composed primarily of nonpolar amino acids. Because polar units solubilise better in water due to the dipole moment interaction with the water molecule.

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