An inhibitor is usually a small molecule that either binds to the substrate or to the enzyme, or to the enzyme-substrate complex. Through its binding it alters the enzyme or substrate conformation, hinders the binding of the both or hinders the complex to dissotiate, decreasing or stopping the enzyme activity. There are also different kind of enzyme inhibition, depending on where the inhibitor binds and which enzyme parameters(Km or Vmax) are changed :)
