life11e_ch08

Enzymes can temporarily add chemical groups to substrates

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The side chains (R groups) of an enzyme’s amino acids may be direct participants in making the enzyme’s substrates more chemically reactive (Figure 8.11C).

In acid–base catalysis, the acidic or basic side chains of the amino acids in the active site transfer H⁺ to or from the substrate, destabilizing a covalent bond in the substrate, and permitting it to break.
In covalent catalysis, a functional group in a side chain forms a temporary covalent bond with a portion of the substrate.
In metal ion catalysis, metal ions such as copper, iron, and manganese, which are often firmly bound to side chains of enzymes, can lose or gain electrons without detaching from the enzymes. This ability makes them important participants in oxidation–reduction reactions, which involve the loss or gain of electrons.