What is allosteric regulation of enzymes?

Allosteric regulation controls enzyme activity through binding of effector molecules at sites other than the active site (allosteric sites). This binding causes conformational changes that affect substrate binding and/or catalytic activity. Allosteric activators stabilize the active conformation (R state), increasing activity, while allosteric inhibitors stabilize the inactive conformation (T state). This regulation enables metabolic feedback control - for example, ATP inhibits and AMP activates phosphofructokinase in glycolysis. Allosteric enzymes often show sigmoidal kinetics rather than hyperbolic Michaelis-Menten kinetics, allowing ultrasensitive responses to substrate changes.