 However, due to its toxic properties, proteins such as Hemopexin (Hx) are required to help maintain physiological stores of iron in order for them to be used in synthesis.Heme is seen as an intermediate molecule in catabolism of hemoglobin in the process of bilirubin metabolism.Defects in various enzymes in synthesis of heme can lead to group of disorder called porphyrias, these include acute intermittent porphyria, congenital erythropoetic porphyria, porphyria cutanea tarda, hereditary coproporphyria, variegate porphyria, erythropoietic protoporphyria.