Properties of Enzymes

Enzymes share several defining properties:

• Proteinaceous nature: with the sole exception of ribozymes (catalytic RNA), every enzyme is fundamentally a protein.
• Three-dimensional conformation: each enzyme folds into a specific 3-D shape and carries one or more active sites — the precise region where the substrate (the reactant molecule the enzyme acts on) binds; the point on the active site where the substrate attaches is called the substrate-binding site.
• Catalytic property: like an inorganic catalyst, an enzyme speeds up the reaction it catalyses without itself being consumed or permanently altered — once a reaction cycle is complete and the product is released, the enzyme is regenerated and free to catalyse the same reaction again. Because of this, a very small quantity of enzyme can process a very large quantity of substrate: sucrase, for example, can hydrolyse roughly 100,000 times its own weight of sucrose.
• Specificity of action: perhaps an enzyme's most distinctive property is that it will catalyse essentially one particular reaction (or a very small number of closely related ones) and no other, acting only on its own specific substrate or class of substrates.

Enzymes are also markedly sensitive to their environment — particularly to temperature and pH. Every enzyme shows its highest activity at one particular pH, its optimum pH; moving the pH up or down from that value reduces enzyme activity. Pepsin, for instance (secreted in the stomach), is most active at an acidic optimum pH of about 2, while trypsin (active in the duodenum) is most active at an alkaline optimum pH of about 9.5 — even though both are protein-digesting enzymes. …