A nonprotein component that combines with and activates an enzyme is called a(n) .

The term you're looking for is "cofactor." A cofactor is a nonprotein chemical compound or metallic ion that is required for the biological activity of a protein, often an enzyme. Cofactors can be divided into two categories:

1. Inorganic cofactors - These include metal ions such as zinc, iron, and magnesium that bind to the enzyme and are necessary for its activity.
2. Organic cofactors - These are known as coenzymes and include vitamins and other organic molecules that assist in enzyme function.

Cofactors play a crucial role in facilitating the biochemical reactions that enzymes catalyze by stabilizing transition states, providing reactive groups for the formation or breaking of chemical bonds, or participating in the electron transport chain. Understanding the function of cofactors is essential in biochemistry and molecular biology, as they help in elucidating the mechanisms of enzyme action and the overall metabolic pathways in cells.