Section 4.12: Myoglobin and Hemoglobin

Myoglobin and hemoglobin are proteins that evolved to carry oxygen in the blood streams of vertebrate organisms. This was an important innovation that enabled a reduced viscosity compared to circulatory systems in which oxygen carriers where directly dissolved in the blood plasma
The red color of blood results from the oxygenated forms of myoglobin and hemoglobin, which is caused by a change in the electrical state of the bound heme prosthetic group
Myoglobin is a small monomeric molecule that acts as a secondary carrier of oxygen in the muscle tissue. Hemoglobin is the system-wide carrier of oxygen that is transported through the blood by red blood cells (erythrocytes)