How can additional molecules or ions increase the activity of an enzyme?

Molecules or ions which improve the activity of an enzyme are classified as cofactors, coenzymes, or prosthetic groups. Cofactors are often ions, and coenzymes and prosthetic groups are larger molecules. Cofactors and coenzymes bind temporarily to catalyse a reaction, whereas prosthetic groups have such a strong interaction they are seen as part of the enzyme. They may interact with the enzyme by binding at the active site or at an allosteric site (a seperate location), and this binding will alter the shape or charge of the active site of the enzyme so it has a more complementary fit (or binds more strongly) to its substrate. As a result it is more easy to form an enzyme-substrate complex, so more reactions are catalyzed.