6.4: Co-facteurs et coenzymes
Enzymes are proteins made of amino acids. The functional group of each constituent amino acid catalyzes a wide variety of chemical reactions via ionic interactions or acid-base reactions. However, amino acids cannot catalyze oxidation-reduction and group transfer reactions and need to be aided by non-protein components called cofactors. Cofactors are also referred to as the chemical teeth of an enzyme.
Cofactors can be metallic ions or organic molecules called coenzymes. These types of helper molecule can bind covalently to an enzyme as prosthetic groups or transiently as co-substrates.
Cofactors are present in ~30% of mature proteins. They are frequently incorporated into an enzyme as it is folded and involved in its catalytic activity. Magnesium is an essential cofactor for over 300 enzymes in the human body, including DNA polymerase. In this case, the magnesium ion helps form the phosphodiester bond on the DNA backbone. Iron, copper, cobalt, and manganese are other common cofactors.
Many vitamins are coenzymes, such as biotin of the vitamin B family. It is essential in various enzymes that transfer carbon dioxide from one molecule to another. Apart from biotin, NAD+, a derivative of Vitamin B3 and retinol or vitamin A, are some other examples of cofactors essential to our body and must be ingested in our diet, as they cannot be made by the human cells.
