The subunits of enzymes are proteins, and the subunits of proteins are amino acids. The majority of enzymes are classified as proteins, but a select few consist of catalytic RNA molecules instead of protein subunits.
Enzymes participate in numerous metabolic and biological reactions within the human body. They catalyze reactions, or speed up the rate at which they occur, without changing the reactants or the products of the overall reaction. The majority of enzymes can catalyze reactions on their own, but some need additional help. The compounds that help these enzymes catalyze reactions are known as co-factors and are typically inorganic ions or metallo-organic molecules.