Enzymes are simple if they are made of only proteins ( e.g., pepsin, amylase etc.) while conjugated enzymes have an additional non-protein cofactor which may be organic or inorganic. Loosely attached organic cofactor is coenzyme (e.g., NAD+,FAD) while firmly attached one is prosthetic group (e.g., heme, biotin). The intact enzyme-cofactor complex is called holoenzyme. When the cofactor is removed, the remaining protein which is inactive is called apoenzyme.