Identify the true statements regarding the heme group of myoglobin and hemoglobin. the cooperativity of oxygen binding in hemoglobin arises from a shorter fe−o2 bond length in the t state compared to the r state. hemoglobin contains four heme groups. the globin chains of myoglobin and hemoglobin prevent the oxidation of fe2+ to fe3+ , which irreversibly binds oxygen. the iron in the heme group can form six bonds. the fifth is with an imidazole ring of a histidine, and the sixth is with oxygen. a heme group contains four pyrrole rings, which are linked via methene (methine) bridges. the heme group is conjugated. the r state of hemoglobin has greater affinity for o2 than the t state because the iron atom is in the plane of the porphyrin ring.