Catalysis (/kəˈtælᵻsᵻs/) is the increase in the rate of a chemical reaction due to the participation of an additional substance called a catalyst (/ˈkætəlᵻst/), which is not consumed in the catalyzed reaction and can continue to act repeatedly.
Enzyme catalysis is the increase in the rate of a chemical reaction by the active site of a protein. The protein catalyst (enzyme) may be part of a multi-subunit complex, and/or may transiently or permanently associate with a Cofactor (e.g. adenosine triphosphate).
Enzymes are biological catalysts. Catalysts lower the activation energy for reactions. The lower the activation energy for a reaction, the faster the rate. Thus enzymes speed up reactions by lowering activation energy. Many enzymes change shape when substrates bind.
A catalyst is not consumed by the reaction and it may participate in multiple reactions at a time. The only difference between a catalyzed reaction and an uncatalyzed reaction is that the activation energy is different. There is no effect on the energy of the reactants or the products.