A class of proteins that contain
metals, unsurprisingly. All
life seems to require such organometallic catalysts; perhaps because the two
complement each other so well. Metals are electron rich and can adopt many different
oxidation states, while the protein provides a tuned
microenvironment for the metal. Often, sidechains
ligand the ion(s) to modulate thier properties.
Haem iron has four nitrogen ligands from the
porphyrin and one from a
histidine that is attached to the backbone. The oxygen makes up the sixth ligand, when it is bound.