― Animated video showing fate of RBC/hemoglobin ∙ Hemoglobin is a purple-colored, iron-containing respiratory pigment of cytoplasm of RBC. Hemoglobin is a conjugated protein and is formed of 4 heme groups and a protein called globin. Each heme group contains an iron-containing porphyrin ring formed of 4 pyrrole rings. Globin is formed of 4 polypeptide chains—2a and 2p chains. One RBC possess about ... .