noun, plural: cofactors
Cofactors pertain to the inorganic substances that are needed by certain enzymes to carry out catalysis of a particular chemical reaction. Cofactors are non-protein compounds. However, they are involved in catalysis by binding to enzymes at their specific binding sites in order to activate them. Examples of cofactors are as follows: Zn++ (binds to carbonic anhydrase or alcohol dehydrogenase), Fe+++ or Fe++ (reacts with cytochromes, hemoglobin, and ferredoxin), Cu++ or Cu+ (binds to cytochrome oxidase), and K+ and Mg++ (bind to pyruvate phosphokinase). Cofactors are considered as helper molecules because they assist in biochemical transformations.
In certain literature, cofactors include the coenzymes, which are also nonprotein compounds but are organic substances. Examples of coenzymes are nicotine adenine dinucleotide (NAD), nicotine adenine dinucelotide phosphate (NADP), and flavine adenine dinucleotide (FAD) involved in oxidation or hydrogen transfer. Coenzyme A (CoA) is another coenzyme involved in the transfer of acyl groups.