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In animals, there are two major globin proteins that bind to oxygen: hemoglobin and myoglobin.

Hemoglobin (Hb) is a protein present in the red blood cells of almost all vertebrates. Its primary function is to transport oxygen from the lungs to the body's tissues and to collect carbon dioxide from tissues and transport it back to the lungs. Hemoglobin has a high affinity for oxygen, allowing it to effectively capture oxygen molecules when the blood is exposed to oxygen-rich environments. Hemoglobin is composed of four polypeptide chains, each containing an iron-bound heme group that can bind an oxygen molecule.

Myoglobin (Mb) is an oxygen-binding protein found primarily in muscle tissue, especially in the heart and skeletal muscles. Its primary function is to store and transport oxygen within the muscle cells, making it readily available for cellular respiration. Myoglobin has a higher affinity for oxygen than hemoglobin, which allows it to better store oxygen in muscles during low-oxygen conditions. Just like hemoglobin, myoglobin contains a heme group bound to an iron ion, and this heme group is responsible for oxygen binding. However, myoglobin is composed of only one polypeptide chain, as opposed to the four chains found in hemoglobin. In summary, the two oxygen-binding globin proteins in animals are hemoglobin and myoglobin. Hemoglobin transports oxygen from the lungs to the tissues and carries carbon dioxide back to the lungs, while myoglobin stores and transports oxygen within muscle cells to support cellular respiration.