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Allosteric enzymes respond to effectors that stabilize different conformational states. A substrate can act as a homotropic effector, producing cooperativity and a sigmoidal velocity-versus-substrate curve. Heterotropic effectors are other molecules: activators shift the curve toward lower K₀.₅, while inhibitors shift it toward higher K₀.₅. These changes primarily affect apparent affinity, though Vmax may also change. Allostery supports rapid, reversible metabolic control through mechanisms such as feedback inhibition by pathway end products and feed-forward activation by upstream metabolites. It can also interact with covalent modification. Recognizing a sigmoidal rather than Michaelis–Menten hyperbolic kinetic pattern is a useful clue to allosteric behavior.