Hemoglobin is an essential protein in the body, performing the major part of the oxygen transport in the blood. Hemoglobin contains iron which gives it a red color, and it contributes that color to the red blood cells and the blood itself.
Hemoglobin consists of two types of components call heme and globin. Globin is a protein of 574 amino acids in four polypeptide chains. Each of those chains is associated with a heme group. Each heme group surrounds an atom of iron, and each iron atom can loosely bind an oxygen atom. Binding up to four oxygen molecules, the hemoglobin forms the compound called oxyhemoglobin.
Shipman, Wilson and Todd