Editing Prosthetic group (section)

{{Short description|Covalently bonded non-protein part of an enzyme}}
A '''prosthetic group''' is the non-amino acid component that is part of the structure of the heteroproteins or [[Conjugated protein|conjugated proteins]], being tightly linked to the [[Apoenzyme|apoprotein]].

Not to be confused with the [[cosubstrate]] that binds to the [[enzyme]] apoenzyme (either a [[holoprotein]] or heteroprotein) by non-covalent binding a non-protein (non-[[amino acid]]) 

This is a component of a [[conjugated protein]] that is required for the protein's biological activity.<ref>{{cite web |url=http://www.chem.qmul.ac.uk/iupac/bioinorg/PR.html#24 |title=Glossary of Terms Used in Bioinorganic Chemistry: Prosthetic groups |accessdate=2007-10-30 |last=de Bolster |first=M.W.G. |date=1997 |publisher=International Union of Pure and Applied Chemistry |archive-url=https://web.archive.org/web/20121128194239/http://www.chem.qmul.ac.uk/iupac/bioinorg/PR.html#24 |archive-date=2012-11-28 |url-status=dead }}</ref> The prosthetic group may be [[organic compound|organic]] (such as a [[vitamin]], [[sugar]], [[RNA]], [[phosphate]] or [[lipid]]) or [[inorganic]] (such as a [[metal]] ion). Prosthetic groups are bound tightly to proteins and may even be attached through a [[covalent bond]]. They often play an important role in [[enzyme catalysis]]. A protein without its prosthetic group is called an [[Apoenzyme|apoprotein]], while a protein combined with its prosthetic group is called a [[holoprotein]]. A non-covalently bound prosthetic group cannot generally be removed from the holoprotein without denaturating the protein. Thus, the term "prosthetic group" is a very general one and its main emphasis is on the tight character of its binding to the apoprotein. It defines a ''structural'' property, in contrast to the term "[[coenzyme]]" that defines a ''functional'' property.

Prosthetic groups are a subset of [[Cofactor (biochemistry)|cofactors]]. Loosely bound metal ions and coenzymes are still cofactors, but are generally not called prosthetic groups.<ref>Metzler DE (2001) Biochemistry. The chemical reactions of living cells, 2nd edition, Harcourt, San Diego.</ref><ref>Nelson DL and Cox M.M (2000) Lehninger, Principles of Biochemistry, 3rd edition, Worth Publishers, New York </ref><ref>Campbell MK and Farrell SO (2009) Biochemistry, 6th edition, Thomson Brooks/Cole, Belmont, California</ref> In enzymes, prosthetic groups are involved in the catalytic mechanism and required for activity. Other prosthetic groups have structural properties. This is the case for the sugar and lipid moieties in [[glycoproteins]] and [[lipoproteins]] or [[RNA]] in ribosomes. They can be very large, representing the major part of the protein in [[proteoglycans]] for instance.

The [[heme]] group in [[hemoglobin]] is a prosthetic group. Further examples of organic prosthetic groups are vitamin derivatives: [[thiamine pyrophosphate]], [[pyridoxal-phosphate]] and [[biotin]]. Since prosthetic groups are often vitamins or made from vitamins, this is one of the reasons why vitamins are required in the human diet. Inorganic prosthetic groups are usually [[transition metal]] ions such as [[iron]] (in [[heme]] groups, for example in [[cytochrome c oxidase]] and [[hemoglobin]]), [[zinc]] (for example in [[carbonic anhydrase]]), [[copper]] (for example in [[complex IV]] of the respiratory chain) and [[molybdenum]] (for example in [[nitrate reductase]]).