Catalyzes the ferrous insertion into protoporphyrin IX (PubMed:9712849). Terminal enzyme in heme biosynthesis (PubMed:9712849). Contains four conserved cysteines that function as cluster ligands and play a crucial role in maintaining protein structure (PubMed:9712849). 2 H(+) + heme b = Fe(2+) + protoporphyrin IX Binds 1 [2Fe-2S] cluster. Porphyrin-containing compound metabolism; protoheme biosynthesis; protoheme from protoporphyrin-IX: step 1/1. Monomer. Belongs to the ferrochelatase family.