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Metalloproteins are abundant in nature where it is estimated that they are present in around half of all proteins. They are defined by having at least one metal ion present within the protein. Metalloenzymes form a subgroup within the metalloprotein grouping and are defined by playing an active role in a catalytic process. Not all metalloproteins are metalloenzymes, some metal ions present in metalloproteins play a structural role for example, allowing the protein to fold around the metal ion (e.g. Zn fingers).
Examples of natural metalloenzymes include hydrogenases, which breaks down diatomic hydrogen atoms with a catalytic site containing a single Fe ion or a combination of Fe-Fe or Fe-Ni ions. This hydrogenation reaction is a very common transformation but for chemical synthesise, it usually relies on precious metal Pt or Pd catalysts.
Another example is nitrogenase a metalloenzyme which catalyses the breakdown of the strong diatomic nitrogen triple bond to form ammonia. The catalytic site involves a cluster of 7 Fe ions and sulphur atoms around a central Mo ion. The equivalent industrial process is the Haber (-Bosch) process, which is used to produce fertiliser and is one of the highest energy consuming/CO2 producing processes in modern industrial chemical production.
Understanding how complex metalloenzymes (or specifically their complex active sites) function to catalyse synthetically demanding reactions such as those described above, highlights how researchers can draw upon nature to develop next generation catalysts.
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