The molecular weight of myoglobin depends on what organism's myoglobin is being used. For calibration in mass spectrometry, horse myoglobin and sperm whale myoglobin are the most common. Horse myoglobin has a molecular weight of 16,951.49, and the myoglobin from sperm whales has a molecular weight of 17,199.91.
Myoglobin is a small, red protein that is found in muscles. It binds oxygen molecules and supplies them when the muscle is working. The red color of meat is largely because of myoglobin proteins. Aquatic mammals that dive for extended periods of time, like dolphins or sperm whales, have more myoglobin than other mammals. This gives them an extra store of oxygen so they can come up for air less often.