he heme prosthetic group consists of protoporphyrin and an iron (II) ion. is the reason for cooperative binding of O2 by hemoglobin. is found only in myoglobin and hemoglobin. is the reason for cooperative binding of O2 by myoglobin.

The correct answer is ''consists of protoporphyrin and an iron (II) ion.''

Explanation:

The heme group makes up the prosthetic (non-protein) group of hemoglobin and is responsible for its characteristic red color. It is composed of protoporphyrin IX, in the center of which is the ferrous ion (Fe+2). Protoporphyrin IX, in turn, is composed of four pyrrolic rings. The heme group is synthesized by the mitochondria, where protoporphyrin IX binds with the ferrous ion, before being released into the cytoplasm. The heme group is released in erythrocyte lysis, thus obtaining unconjugated or indirect bilirubin.