Enzymes

Enzymes are proteins which catalyze biochemical reactions but are not used up within the reaction themselves. In terms of the Laws of Thermodynamics, enzymes reduce the activation energy of a given step in an equilibrium reaction.

Enzymes exhibit abolished function at high temperatures - the become denatured. Also, they are usually specific for a given substrate molecule which may even have to demonstrate orientation in a given direction - stereospecifity.