Catalyzes the ferrous insertion into protoporphyrin IX. 2 H(+) + heme b = Fe(2+) + protoporphyrin IX Porphyrin-containing compound metabolism; protoheme biosynthesis; protoheme from protoporphyrin-IX: step 1/1. It is bound to the mitochondrial inner membrane in eukaryotic cells with its active site on the matrix side of the membrane. The leader peptide may be processed in two proteolytic steps, first between Ser-23 and Phe-24, second and by a different protease, to yield the mature protein. Ferrochelatase interacts with protoprophyrinogen oxidase, and associates with complex 1 of the respiratory chain. Acidic phospholipids or fatty acids are important for the ferrochelatase activity. Present with 22700 molecules/cell in log phase SD medium. Belongs to the ferrochelatase family.