Non-competitive inhibitors are molecules that bind to an enzyme at a site other than the active site, which is where the substrate normally binds. This binding changes the enzyme's shape, reducing its ability to catalyze a reaction, regardless of the substrate concentration. As a result, the maximum rate of reaction decreases, but the affinity for the substrate remains unchanged. These inhibitors can be important in regulating metabolic pathways. For example, in the presence of a non-competitive inhibitor, the enzyme can still bind to the substrate, but the overall reaction rate is lowered. This mechanism helps maintain balance in biological systems, such as those involving enzymes and metabolism.