Metalloprotein

A metalloprotein is a protein that contains a metal ion cofactor. A large fraction of all proteins are members of this category, so the number is very large.
It is estimated that about half of all proteins contain a metal. In another estimate, about one-quarter to one-third of all proteins need metals to carry out their functions. Thus, metalloproteins have many different functions in cells, such as enzymes, transport and storage proteins, and signal transduction proteins.