The focus of this research was the characterization of three metallroteins. The characterization was based on the information obtained from their structures and biochemical data obtained from in-vitro and in-vivo experiments. The structures of the three proteins studied were obtained by x-ray crystallography. The first protein studied was the hemerythrin-like domain from the Desulfovibrio vulgaris chemoreceptor H, DcrH-Hr. The second protein was the Bacillus subtilis M32 carboxypeptidase, BsuCP. And the third protein was one of the M32 carboxypeptidases from Leishmania major, LmaCP.