What are co-factors? Describe their types.

(N/A) $\rightarrow$ Enzymes are composed of one or several polypeptide chains. Generally,non-protein constituents called co-factors are bound to the enzyme to make it catalytically active.
$\rightarrow$ The protein portion of the enzyme is called the apoenzyme.
$\rightarrow$ Three kinds of co-factors are identified:
$\rightarrow$ $(1)$ Prosthetic groups,$(2)$ Co-enzymes,$(3)$ Metal ions.
$\rightarrow$ $(1)$ Prosthetic groups: These are organic compounds that are tightly bound to the apoenzyme. For example,in peroxidase and catalase,which catalyze the breakdown of hydrogen peroxide to $H_{2}O$ and $O_{2}$,haem $(Fe^{++})$ is the prosthetic group and is a part of the active site of the enzyme.
$\rightarrow$ $(2)$ Co-enzymes: These are also organic compounds,but they are associated temporarily with the apoenzyme.
$\rightarrow$ They serve as co-factors in a number of different enzyme-catalyzed reactions.
$\rightarrow$ Many co-enzymes have vitamins as their components; for example,co-enzyme nicotinamide adenine dinucleotide $(NAD)$ and $NADP$ contain the vitamin niacin.
$\rightarrow$ $(3)$ Metal ions: These are essential for the activity of many enzymes. They form coordination bonds with side chains at the active site and simultaneously form one or more coordination bonds with the substrate. For example,zinc is a co-factor for the enzyme carboxypeptidase. Catalytic activity is lost when the co-factor is removed from the enzyme.