Hemin is a dark brown or reddish-brown crystalline compound derived from the breakdown of hemoglobin, the protein in red blood cells that carries oxygen. It is primarily composed of iron and porphyrin, and it plays a crucial role in various biological processes, including the synthesis of hemoglobin and the regulation of heme levels in the body. In medical and laboratory settings, hemin is often used to treat certain conditions, such as acute intermittent porphyria, a disorder that affects the production of heme. It can also serve as a reagent in biochemical research, helping scientists study the functions of heme-containing proteins.