<unk> s are small organic non-protein molecules that carry chemical groups between enzymes.<unk> s are sometimes referred to as<unk> substrates. These molecules are substrates for enzymes and do not form a permanent part of the enzymes' structures. This distinguishes<unk> s from prosthetic groups, which are non-protein<unk> mponents that are bound tightly to enzymes - such as iron-sulfur centers, flavin or haem groups. Both<unk> s and prosthetic groups are types of the broader group of<unk> factors, which are any non-protein molecules (usually organic molecules or metal ions) that are required by an enzyme for its activity.
In metabolism,<unk> s are involved in both group-transfer reactions, for example<unk>  A and adenosine triphosphate (ATP), and redox reactions, such as<unk>  Q10 and nicotinamide adenine dinucleotide (NAD+).<unk> s are<unk> nsumed and recycled<unk> ntinuously in metabolism, with one set of enzymes adding a chemical group to the<unk>  and another set removing it. For example, enzymes such as ATP synthase<unk> ntinuously phosphorylate adenosine diphosphate (ADP),<unk> nverting it into ATP, while enzymes such as kinases dephosphorylate the ATP and<unk> nvert it back to ADP.<unk> s molecules are often vitamins or are made from vitamins. Many<unk> nezymes<unk> ntain the nucleotide adenosine as part of their structures, such as ATP,<unk>  A and NAD+. This<unk> mmon structure may reflect a<unk> mmon evolutionary origin as part of ribozymes in an ancient RNA world.
Coenzyme
Flavin
Carbonyl
Carbide
Oxamyl
Hemin
Oxoacid
Substrate 