Metalloproteins are attractive biomaterials, because metal ions generally possess a variety of physicochemical properties and catalytic behaviors. Furthermore, a protein matrix provides an effective metal coordination space that regulates metal ion reactivity. Over the last four decades, many kinds of metalloprotein structures have been determined, and their characteristics give us important and detailed insights into protein functions in details. Therefore, one of our next our research targets is engineering a metalloprotein to create tailor-made biomaterials. To achieve this, we have focused on hemoproteins, typical metalloproteins with a heme (an iron porphyrin complex) prosthetic group. The functions of hemoproteins are widely varied: electron transfer, O₂ dioxygen storage/transport, O₂ and CO sensding, NO transport, oxidation catalysis etc., although thoese proteins have the common prosthetic group, heme. These findings strongly suggest that the modification of the heme active site will serve as a new strategy to produce a unique functionalized metalloprotein. Thus, our group's efforts have been devoted to the preparation of designed metalloporphyrins and to the construction of unique proteins reconstituted with an artificially created heme. Our goal is to create a new interdisciplinary field based on organic chemistry , coordination chemistry and biochemistry, and then to construct various biomaterials such as biocatalysts, sensors or medical materials.