Myoglobin. Molecular graphic of the oxygen- carrying protein myoglobin. Myoglobin consists of a chain of amino acids folded into a globin molecule, which is similar to the four globin subunits in haemoglobin. Coloured spheres here represent atoms in the chain. The dark region in the centre is the haem group, which contains a single iron atom to which a molecule of oxygen can form a temporary bond. Myoglobin is found in muscle tissue, where it stores additional oxygen for use during strenuous exercise.