Hemoglobin is the major component of red blood cells and is responsible for their red color. Its normal concentration in erythrocytes is 34%. The structure of horse hemoglobin was elucidated first. It comprises heme (iron protoporphyrin IX group) and four polypeptide chains. The fetal and adult hemoglobin of horse are structurally identical.

Hemoglobin equine has been used as a standard protein:

• to test solid-film sampling methodology in Fourier transform infrared spectroscopy (FT-IR) for protein secondary structure determination
• in capillary reversed-phase liquid chromatography-tandem mass spectrometry (LC/MS/MS) post enzymatic digestion
• for quantification of hemoglobin content from the planktonic crustacean, Daphnia magna

Oxygen transporter, NO scavenger

Hemoglobin is the most important respiratory protein of vertebrates by its ability to transport oxygen from the lungs to body tissues and to facilitate the return transport of carbon dioxide. The ferrous-ferric (Fe²⁺/Fe³⁺) balance is a physiological indicator of blood oxygenation. Deoxygenated hemoglobin accessorizes a feedback loop by reducing nitrite to nitric oxide (NO), a vasodilator which enhances blood flow to oxygen-deprived tissues. The fetal and adult hemoglobin from horse display differences in their affinity towards 2,3-diphosphoglycerate (2,3-DPG). Mutation in the globin gene is implicated in sickle cell anemia.

Since native hemoglobin is readily oxidized in air, these preparations may be predominantly methemoglobin.