Enzymes

Enzymes as biocatalysts

A living organism survives because thousands of chemical reactions inside it run in a coordinated sequence — digesting food, absorbing the useful molecules, and finally releasing energy from them is one such chain of events. What makes this remarkable is that the whole chain proceeds smoothly at body temperature and under otherwise mild physiological conditions, something ordinary laboratory chemistry would struggle to do without heating, strong acids/bases, or high pressure. This is possible because living systems use their own class of catalysts, called enzymes, which speed up these reactions under gentle conditions.

Structurally, enzymes are almost entirely globular proteins — compact, roughly spherical protein molecules whose folded shape is essential to how they work (see the protein structure discussion earlier in this chapter).

Specificity of enzymes

The defining feature of an enzyme, compared to an ordinary chemical catalyst, is its specificity. A general chemical catalyst (say, a metal surface or an acid) will often accelerate a whole class of reactions on many different substrates. An enzyme, in contrast, is tailored to act on one particular substrate, or a closely related family of substrates, and to catalyse essentially only that one reaction. This precision is one of the reasons biochemical pathways can run in an organism without side reactions running out of control.

Naming enzymes

Enzyme names generally follow two conventions:

By substrate — the enzyme's name is built from the name of the compound (or class of compounds) it acts on, with the ending "-ase" attached. The enzyme that hydrolyses the disaccharide maltose into glucose, for example, is called maltase.

By reaction type — sometimes the enzyme is instead named after the kind of reaction it carries out. An enzyme that catalyses the oxidation of one substrate while simultaneously reducing another is classed as an oxidoreductase.

In both conventions, the family suffix "-ase" is the common signature that marks a molecule as an enzyme. …