Enzymes in Metabolism and Nutrition

Enzymes are biological compounds that are protein in nature, that are soluble in water and that catalyze biochemical reactions. They are also called bio-catalysts.
Enzymes are synthesized by living organisms from models that vary from one species to the other, but they are constant and transmitted hereditarily within the same species; some hereditary illnesses can be explained by a defect in one of these models.

Enzyme Formation
Enzymes are generally proteins. A large number of enzymatic systems result from the binding of two molecules:

• The first one is a protein and is destroyed by heat; it is responsible for substrate specificity and is called an “apoenzyme.”
• The second is not a protein and is not destroyed by heat; it participates directly in the reaction and is called a “coenzyme.” We can therefore state that:

Enzyme = Apoenzyme + coenzyme

Apoenzymes
The protein part where the active site composed of several amino acids (that assemble in the secondary and tertiary structures, but move away in the primary structure) is found.
On the active site, there are generally two sites:

• The binding site, where the substrate (the material to be transformed) and the coenzyme (also called a metallic ion) become attached
• The catalytic site, where the enzymatic action occurs.

Coenzymes
A smaller and more resistant molecule that results most often from the union of a nucleotide and a B vitamin (thiamine, flavin, pyridoxine, niacin, pantothenic acid). Sometimes it is a simple metal ion.
: A single coenzyme can bind to make apoenzymes.
[excerpt from the AMCC's Metabolism and Nutrition course manual. Register today!]