What is the term for an organic cofactor required for the proper functioning of an enzyme?

The term for an organic cofactor required for the proper functioning of an enzyme is "coenzyme." Coenzymes are non-protein, organic molecules that assist enzymes by accepting or donating specific atoms or functional groups during the enzymatic reaction. Many vitamins act as coenzymes, playing crucial roles in metabolic processes by working alongside enzymes to facilitate biochemical reactions.

In contrast, substrates refer to the specific reactants that an enzyme acts upon. Catalysts are substances that speed up reactions without being consumed, but they do not necessarily refer to organic cofactors. Enzymes are biological catalysts themselves, which means they are proteins that facilitate chemical reactions, but they can require coenzymes to function optimally. Therefore, the correct term specifically emphasizing the organic nature and role in enzymatic activity is indeed coenzyme.