A cofactor is a non-protein chemical compound or metallic ion that is required for an enzyme’s activity as a catalyst. They are therefore, molecules that increase the rate of reaction or are required for enzyme function.
Examples of cofactors include metal ions like iron and zinc.
Cofactors typically differ from ligands in that they often derive their function by remaining bound.
Cofactors can be divided into two types: inorganic ions and complex organic molecules called coenzymes. Coenzymes are mostly derived from vitamins and other organic essential nutrients in small amounts. (Note that some scientists limit the use of the term "cofactor" to inorganic substances; both types are included here
Cofactors can be divided into two major groups: organic cofactors, such as flavin or heme; and inorganic cofactors, such as the metal ions Mg2+, Cu+, Mn2+ and iron-sulfur clusters.
Some enzymes or enzyme complexes require several cofactors. For example, the multienzyme complex pyruvate dehydrogenase at the junction of glycolysis and the citric acid cycle requires five organic cofactors and one metal ion: loosely bound thiamine pyrophosphate (TPP), covalently bound lipoamide and flavin adenine dinucleotide (FAD), cosubstrates nicotinamide adenine dinucleotide (NAD+) and coenzyme A (CoA), and a metal ion (Mg2+).
Organic cofactors are often vitamins or made from vitamins. Many contain the nucleotide adenosine monophosphate (AMP) as part of their structures, such as ATP, coenzyme A, FAD, and NAD+. This common structure may reflect a common evolutionary origin as part of ribozymes in an ancient RNA world. It has been suggested that the AMP part of the molecule can be considered to be a kind of "handle" by which the enzyme can "grasp" the coenzyme to switch it between different catalytic.
A specific type of cofactor, coenzymes, are organic molecules that bind to enzymes and help them function. The key here is that they’re organic. ‘Organic’ does not mean you’ll find them in a special aisle in the grocery store. Rather, organic molecules are simply molecules that contain carbon. Don’t let the name ‘coenzymes’ fool you, either; coenzymes are not really enzymes. As the prefix ‘co-‘ suggests, they work with enzymes. Many coenzymes are derived from vitamins.
These molecules often sit at the active site of an enzyme and aid in recognizing, attracting, or repulsing a substrate or product. Remember that a substrate is the molecule upon which an enzyme catalyzes a reaction. Coenzymes can also shuttle chemical groups from one enzyme to another enzyme. Coenzymes bind loosely to enzymes, while another group of cofactors do not.