Final answer:
An apoenzyme consists solely of protein and becomes an active holoenzyme when it binds with its nonprotein cofactor, which may be a metal ion or an organic molecule known as a coenzyme.
Step-by-step explanation:
A apoenzyme consists of protein alone, while a holoenzyme consists of protein and nonprotein components, also known as cofactors. When an apoenzyme binds to its necessary cofactor, it becomes an active holoenzyme. A cofactor can be either an inorganic metal ion, such as Zn²+ or Mg²+, or an organic compound, which is known as a coenzyme. Examples of coenzymes include biotin and pyridoxine, which often derive from vitamins. Organic or inorganic cofactors enable the enzyme's optimal performance. The intricate relationships between these components are crucial for the catalytic functions of enzymes in biological processes.