ABSTRACT
Porphyrins are tetracyclic molecules (168) named for the Greek word for purple (porphuros). Because of their delocalized electronic structure porphyrins can shuttle electrons around and chelate metal ions. This makes them the principal molecules of energy capture and transfer. As such, porphyrin-containing proteins are involved in diverse and fundamental biochemical processes such as oxygen transport (hemoglobin), light capture (chlorophyll), antioxidant defense (catalase), and xenobiotic metabolism (P450 enzymes). The porphyrins are found as metal ion-bound prosthetic groups within these key enzymes, and mediate the transfer of electrons during the metabolic reactions that are catalyzed by them. The two most important prosthetic groups are heme (iron-chelated porphyrin) and chlorophyll (magnesium-chelated porphyrin). In fact the heme prosthetic group is so fundamental to life that its biosynthesis is one of the most highly conserved biochemical pathways.
