Metalloprotein

A metalloprotein is a protein with a metal ion cofactor.^[1] Many proteins are members of this category, so the number of them is large.

The structure of hemoglobin. The haeme cofactor, containing iron, shown in green.

It is estimated that about half of all proteins contain a metal.^[2] In another estimate, about one-quarter to one-third of all proteins need metals to carry out their functions.^[3] Thus, metalloproteins have many different functions in cells, such as enzymes, transport and storage proteins, and signal transduction proteins.