Bioinorganic chemistry is a branch of inorganic chemistry that involves research into chiefly how metal ions interact with living tissue, mainly through their direct effect on enzyme activity. It is estimated that one-third of enzymes and proteins in the human body rely upon metal ions to function properly in several key ways. These biological areas use proteins with metal ions present to transfer energy via electrons, to transport oxygen, and for nitrogen metabolism. Hydrogenase is also affected by metal ions in the body, which is a microorganism-based enzyme responsible for the transfer of hydrogen, as well as alkyltransferases, which are enzymes responsible for the transfer of alkyl chemical groups among molecules. There are over a dozen metals that are involved in such processes, including zinc, iron, and manganese, with vitamin-based metal elements also playing important roles in such activity like potassium and calcium.
Each group of metal ions performs a select range of functions in bioinorganic chemistry. Both sodium and potassium act as electron charge carriers and maintain a charge balance across permeable membranes. Magnesium, calcium, and zinc perform structural roles at the cellular level, and magnesium and zinc in particular can catalyze the process of hydrolysis where compounds are broken down in a water solution. Metal ions such as molybdenum act as a nitrogen fixater while iron and copper aid in the transport of oxygen. While these are all important functions in the body, the principles of bioinorganic chemistry only require trace elements of metal ions such as manganese, lithium, and molybdenum to perform these types of functions and an overabundance of them can be toxic and even lethal.
In many cases, biochemistry for animals involves cooperative efforts with bacteria present in the body. Bioinorganic chemistry relies upon this symbiotic relationship with examples like the metal ions of vanadium and molybdenum, as they help nitrogen-fixing bacteria to function in the body, or hydrogenase-based organisms that transport hydrogen. While many of these metals are introduced into the body from the diet or are present in bacteria, some exist as components of metalloproteins as well, which are protein molecules with naturally-attached metal ion structures.
Aside from the natural physiological activity of metal ions in bioinorganic chemistry, they are also a subject of study in pharmaceutical research. Attaching metal ions to drugs can enable them to be more readily metabolized by the body. This diversity of functions for metal ions results in their study by a range of natural sciences that work in inorganic chemistry from environmental chemistry to toxicology and specialized fields like enzymology.