Metal ions are involved in many important biological processes, including transcriptional/translational controls, digestions, and regulations. Some examples are given here. More examples can be found in several "Bioinorganic Chemistry" books in the library.

Cu(II) is found in cytochrome oxidase which is the terminal oxidase in aerobic metabolism, in amino acid oxidase, in ascorbic acid oxidase, in superoxide dismutase, in the "blue blood" (hemocyanin) of the invertebrates, and so on.

Zn(II) is found in numerous proteases (such as collagenase, endopeptidase, carboxypeptidase, aminopeptidase, and prolyloligopeptidase), phosphoesterases, nucleases, carbonic anhydrase (which controls the pH in our body), DNA/RNA polymerase, transcription control factors, and many more. Zn protein family indeed contains the largest number of proteins.

Fe (II/III) is found in hemoglobin and myoglobin, ribonucleotide reductase, methane oxygenase (which convert methane into methanol at room temperature very effectively, whereas this conversion is not successful both in the laboratory and in industry), several dioxygenases, isopenicillin N synthase (isopenicillin N is the precursor of all penicillins and cephalosporins), in catalase (which convert hydrogen peroxide into oxygen and water to show the forms on minor cuts), transferin (an iron transfer protein), and ferretin (an iron storage protein), etc.

Mn(II) is found in kinases, and is also involved in photosynthesis in green plants.

Mo (element #42) is found in the nitrogen fixation enzyme "nitrogenase" which convert nitrogen in the air directly into ammonia to incorporated nitrogen into biomolecules (whereas industrial method, the Haber process, uses high pressure at 100 to 1000 atm and high temperature 400 to 550 ºC).