Allosteric modulators bind away from the active, orthosteric, sites of enzymes, allowing their effect to occur without regard for substrate concentration.
Due to the active site still being accessible, allosteric modulators are able to have a positive or negative effect. For example, benzodiazepines are positive allosteric modulators of the GABA_A receptor, increasing the excitability of inhibitory neurotransmission.
By altering the secondary structure of the active site of the enzyme or protein, allosteric modulators can improve or inhibit substrate binding to the orthosteric site. The catalytic process can also be improved or suppressed by allosteric modulators, again through alterations in the enzyme’s secondary structure.