Ferrochelatase at the millennium: structures, mechanisms and [2Fe-2S] clusters

Ferrochelatase (E.C. 4.99.1.1, protoheme ferrolyase) catalyzes the insertion of ferrous iron into protoporphyrin IX to form protoheme (heme). In the past 2 years, the crystal structures of ferrochelatases from the bacterium Bacillus subtilis and human have been determined. These structures along with years of biophysical and kinetic studies have led to a better understanding of the catalytic mechanism of ferrochelatase. At present, the complete DNA sequences of 45 ferrochelatases from procaryotes and eucaryotes are available. These sequences along with direct protein studies reveal that ferrochelatases, while related, vary significantly in amino acid sequence, molecular size, subunit composition, solubility, and the presence or absence of nitric-oxide-sensitive [2Fe-2S] cluster.