Answer: The Quaternary structure
Explanation: Myoglobin and hemoglobin are both hemeprotiens with the ability to bind oxygen.
Myoglobin is mainly found in muscle tissue and plays a vital role as an intracellular storage site for oxygen. Myoglobin is a monomeric heme protein and has a secondary and tertiary structure. Hemoglobin is vital for the transportation of oxygen from the lungs to the rest of the body as needed. Hemoglobin is a tetrameric hemeprotien with secondary and tertiary structures.
Both hemoglobin and myoglobin are absent of a quaternary structure.