Cofactors and Coenzymes

Some enzymes require additional nonprotein molecules or ions to catalyze specific chemical reactions.

These helpers are called cofactors and can be inorganic or organic.

Inorganic cofactors include metal ions such as magnesium.

During the first step of glycolysis, magnesium acts as a cofactor for hexokinase. It helps the enzyme transfer a phosphate group from ATP to glucose by stabilizing negative charges during the reaction.

This reaction forms glucose 6-phosphate, which then moves forward through glycolysis.

Enzymes can also rely on organic cofactors called coenzymes. Many coenzymes come from vitamins and act as electron carriers between reactions.

Further along in glycolysis, the enzyme glyceraldehyde-3-phosphate dehydrogenase uses NAD⁺ as a coenzyme. As the enzyme acts on glyceraldehyde 3-phosphate, NAD⁺ accepts electrons and a hydrogen ion to form NADH. This reaction forms 1,3-bisphosphoglycerate, which continues through glycolysis.

NADH carries these electrons to other reactions in the cell.

Together, these examples show how metal-ion cofactors and coenzymes support different steps of enzyme-catalyzed reactions.