A holoprotein or conjugated protein is an apoprotein combined with its prosthetic group.
[1] Some enzymes do not need additional components to show full activity.
[2] Cofactors can be either inorganic (e.g., metal ions and iron-sulfur clusters) or organic compounds (e.g., flavin and heme).
Organic prosthetic groups can be covalently bound (e.g., biotin in enzymes such as pyruvate carboxylase).
[4] These tightly bound ions or molecules are usually found in the active site and are involved in catalysis.