How enzymes work

There have been many theories of the exact mechanism of the action of an enzyme because so little of it is needed to affect the rate of a reaction. Some enzymes can speed up a reaction by as much as 10–20 000 times. One explanation for the mechanism is as follows.

In a normal reaction the two reactants need to collide with each other many times for a reaction to occur. In each collision only a few of the molecules are in the correct orientation to actually react with their counterparts, so owing to the randomness of motion, the reaction can take some time. When an enzyme is used, the reactant fits onto the enzyme molecule in the correct specific orientation so that, when the other reactant comes close to the enzyme/reactant combination, it is immediately in the correct orientation and alignment for the two reactants to join up.

These react and then break away from the enzyme and form the new molecule, and the enzyme is available for reuse. Because the reactants are lined up correctly, no time is lost in useless random collisions between the reacting molecules. This mechanism is sometimes referred to as the ‘lock and key’ model.