Allosteric control

Allosteric control or regulation, is when a molecule effects the action of an enzyme, by binding, but NOT to the active site, they bind to a specific allosteric site. On binding, they typically switch on/increase protein activity, or switch off/decrease protein activity. They cause these changes in levels of activity in the enzyme by causing a conformational change in the protein, leading to an alteration in the enzyme's active site, which therefore effects catalytic activity. They form part of a complex system of negative feedback and feedback loops.

References

1. http://www.biology.arizona.edu/biochemistry/problem_sets/energy_enzymes_catalysis/03t.html