Prosthetic group

A prosthetic group is a non-protein (non-amino acid) component of a conjugated protein that is important in the protein's biological activity. The prosthetic group may be organic (such as a vitamin, sugar, 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 the function of enzymes. A protein without its prosthetic group is called an apoprotein, while a protein combined with its prosthetic group is called a holoprotein.

Prosthetic groups are a subset of cofactors and differ from coenzymes in that they bind permanently to the enzyme as opposed to temporarily for coenzymes. In enzymes, prosthetic groups are involved in the active site in some way.

The heme group in hemoglobin is a prosthetic group. Further examples of organic prosthetic groups are vitamin derivatives: thiamine (vitamin B₁), 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), magnesium (for example in some kinases), and molybdenum (for example in nitrate reductase).

List of prosthetic groups

Prosthetic group	Function	Distribution
Flavin mononucleotide	Redox reactions	Bacteria, archaea and eukaryotes
Flavin adenine dinucleotide	Redox reactions	Bacteria, archaea and eukaryotes
Pyrroloquinoline quinone	Redox reactions	Bacteria
Pyridoxal phosphate	Transamination, decarboxylation and deamination	Bacteria, archaea and eukaryotes
Biotin	Carboxylation	Bacteria, archaea and eukaryotes
Methylcobalamin	Methylation and isomerisation	Bacteria, archaea and eukaryotes
Thiamine pyrophosphate	Decarboxylation	Bacteria, archaea and eukaryotes
Heme	Oxygen binding and redox reactions	Bacteria, archaea and eukaryotes
Molybdopterin	Oxygenation reactions	Bacteria, archaea and eukaryotes
Lipoic acid	Redox reactions	Bacteria, archaea and eukaryotes

References

See also

• Cofactor (biochemistry)

External links

• Cofactors PowerPoint lecture