Enzymes are proteinaceous in nature. Some enzymes also contain non-protein parts known as co-factors. These factors are attached to the enzymes to enhanced their catalytic activity. The protein part of the enzyme is known as apoenzyme. Hence, apoenzyme (protein part) + co-factors (non-protein part) = Holoenzyme (whole enzyme). As the co-factors are bound to enzymes, the removal of these factors affects the overall activity of enzymes too. These co-factors can be organic or inorganic. Organic cofactors if tightly bound are known as prosthetic groups and if loosely bound are termed as co-enzymes. The inorganic co-factors are metal ions. Example of an inorganic co-factor is zinc which is a co-factor of enzyme carboxypeptidase.