- Last Update On : 2013-01-28
The heme biosynthetic pathway consists of 8 enzymes. The formation of heme begins with the condensation of glycine and succinyl coenzyme A to delta-aminolevulinic acid (ALA). A series of enzyme reactions converts ALA to porphobilinogen (PBG) and then to various porphyrinogens. Finally, iron is inserted into protoporphyrin by the enzyme ferrochelatase, forming heme.
The majority of heme is produced in erythropoietic cells where it is incorporated into hemoglobin. Hepatocytes also produce a significant amount for use in myoglobin, cytochromes, catalase and peroxidase. Each porphyria is caused by a specific enzyme deficiency involved in the heme biosynthetic pathway.
Most types of porphyria, with the exception of congenital erythropoietic porphyria, are diagnosed in adulthood. The simplest approach to classifying the porphyrias is on the basis of their clinical manifestations. Porphyrias can be divided into two general groups; those causing predominantly acute neurologi