{{Short description|Covalently bonded non-protein part of an enzyme}} A '''prosthetic group''' is a non-amino acid component that is tightly linked to the apoprotein and forms part of the structure of the heteroproteins or conjugated proteins.
It is 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).
A prosthetic group 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> It may be 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 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 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 typically involved in the catalytic mechanism and are required for enzymatic activity; however, other prosthetic groups have structural properties. This is the case for the sugar and lipid moieties found 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 well-known example of 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).
== List of prosthetic groups == The table below contains a list of some of the most common prosthetic groups. {| class="wikitable" ! Prosthetic group || Function || Distribution |- | Flavin mononucleotide <ref name="Joosten">{{cite journal |author=Joosten V, van Berkel WJ |title=Flavoenzymes |journal=Curr Opin Chem Biol |volume=11 |issue=2 |pages=195–202 |year=2007 |pmid=17275397 |doi=10.1016/j.cbpa.2007.01.010}}</ref> || Redox reactions || Bacteria, archaea and eukaryotes |- | Flavin adenine dinucleotide <ref name="Joosten" /> || Redox reactions || Bacteria, archaea and eukaryotes |- |Pyrroloquinoline quinone <ref>{{cite journal | author = Salisbury SA, Forrest HS, Cruse WB, Kennard O | title = A novel coenzyme from bacterial primary alcohol dehydrogenases | journal = Nature | year = 1979 | volume = 280 | issue = 5725 | pages = 843–4 | doi = 10.1038/280843a0| pmid = 471057 | bibcode = 1979Natur.280..843S | s2cid = 3094647 }}</ref> || Redox reactions || Bacteria |- |Pyridoxal phosphate <ref>{{cite journal |author=Eliot AC, Kirsch JF |title=Pyridoxal phosphate enzymes: mechanistic, structural, and evolutionary considerations |journal=Annu. Rev. Biochem. |volume=73 |pages=383–415 |year=2004 |pmid=15189147 |doi=10.1146/annurev.biochem.73.011303.074021}}</ref> || Transamination, decarboxylation and deamination || Bacteria, archaea and eukaryotes |- |Biotin <ref>{{cite journal |author=Jitrapakdee S, Wallace JC |title=The biotin enzyme family: conserved structural motifs and domain rearrangements |journal=Curr. Protein Pept. Sci. |volume=4 |issue=3 |pages=217–29 |year=2003 |pmid=12769720 |doi=10.2174/1389203033487199}}</ref> || Carboxylation || Bacteria, archaea and eukaryotes |- | Methylcobalamin <ref>{{cite journal |author=Banerjee R, Ragsdale SW |title=The many faces of vitamin B12: catalysis by cobalamin-dependent enzymes |journal=Annu. Rev. Biochem. |volume=72 |pages=209–47 |year=2003 |pmid=14527323 |doi=10.1146/annurev.biochem.72.121801.161828|s2cid=37393683 |url=https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1458&context=biochemfacpub |url-access=subscription }}</ref> || Methylation and isomerisation || Bacteria, archaea and eukaryotes |- |Thiamine pyrophosphate <ref>{{cite journal |author=Frank RA, Leeper FJ, Luisi BF |title=Structure, mechanism and catalytic duality of thiamine-dependent enzymes |journal=Cell. Mol. Life Sci. |volume=64 |issue=7–8 |pages=892–905 |year=2007 |pmid=17429582 |doi=10.1007/s00018-007-6423-5|s2cid=20415735 |pmc=11136255 }}</ref> || Transfer of 2-carbon groups, α cleavage || Bacteria, archaea and eukaryotes |- |Heme <ref>{{cite journal |author=Wijayanti N, Katz N, Immenschuh S |title=Biology of heme in health and disease |journal=Curr. Med. Chem. |volume=11 |issue=8 |pages=981–6 |year=2004 |pmid=15078160 |doi=10.2174/0929867043455521}}</ref> || Oxygen binding and redox reactions || Bacteria, archaea and eukaryotes |- |Molybdopterin <ref>{{cite journal |author=Mendel RR, Hänsch R |title=Molybdoenzymes and molybdenum cofactor in plants |journal=J. Exp. Bot. |volume=53 |issue=375 |pages=1689–98 |year=2002 |pmid=12147719 |doi=10.1093/jxb/erf038|doi-access=free }}</ref><ref>{{cite journal |author=Mendel RR, Bittner F |title=Cell biology of molybdenum |journal=Biochim. Biophys. Acta |volume=1763 |issue=7 |pages=621–35 |year=2006 |pmid=16784786 |doi=10.1016/j.bbamcr.2006.03.013|doi-access= }}</ref> || Oxygenation reactions || Bacteria, archaea and eukaryotes |- |Lipoic acid <ref>{{cite journal |author=Bustamante J, Lodge JK, Marcocci L, Tritschler HJ, Packer L, Rihn BH |title=Alpha-lipoic acid in liver metabolism and disease |journal=Free Radic. Biol. Med. |volume=24 |issue=6 |pages=1023–39 |year=1998 |pmid=9607614 |doi=10.1016/S0891-5849(97)00371-7}}</ref> || Redox reactions || Bacteria, archaea and eukaryotes |- |Cofactor F430 |Methanogenesis |Archaea |}
== References == {{reflist|2}}
==External links== *[http://www.bio.mtu.edu/%7Ehlyoungs/BL4010/cofactors.ppt Cofactors PowerPoint lecture] {{Webarchive|url=https://web.archive.org/web/20161005230343/http://www.bio.mtu.edu/%7Ehlyoungs/BL4010/cofactors.ppt |date=2016-10-05 }}
{{Enzyme cofactors}}
Category:Cofactors