Enzyme

An enzyme (from Greek énsimo (??????), formed by én = at or in and simo = leaven or yeast) is a protein that catalyzes, or speeds up, a chemical reaction.

Thermodynamics

As with all catalysts, all reactions catalyzed by enzymes must be "spontaneous" (containing a net negative Gibbs free energy). With the enzyme, they run in the same direction as they would without the enzyme, just more quickly. However, the uncatalyzed, "spontaneous" reaction might lead to different products than the catalyzed reaction. Furthermore, enzymes can couple two or more reactions, so that a thermodynamically favorable reaction can be used to "drive" a thermodynamically unfavorable one. For example, the cleavage of the high-energy compound ATP is often used to drive other, energetically unfavorable chemical reactions.

Related Topics:
Gibbs free energy - ATP

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Many reactions catalyzed by an enzyme are reversible.

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: mathrm{Substrate A + Substrate B leftrightarrow Product C + Product D}

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Enzymes catalyze the forward and backward reactions equally. They do not alter the equilibrium itself, but only the speed at which it is reached, for example, carbonic anhydrase which catalyzes a reaction in either direction depending on the conditions at the time.

Related Topics:
Equilibrium - Carbonic anhydrase

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: mathrm{CO_2 + H_2O

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