Figure 1-1: A flow chart of the two types of cofactors. Apoenzyme-An enzyme that requires a cofactor but does not have one bound. An apoenzyme is an inactive enzyme, activation of the enzyme occurs upon binding of an organic or inorganic cofactor. Holoenzyme-An apoenzyme together with its cofactor. A holoenzyme is complete and catalytically active. Most cofactors are not covalently bound but instead are tightly bound. However, organic prosthetic groups such as an iron ion or a vitamin can be covalently bound.