Enzymes are delicate protein catalysts with subtle conformational flexibilities. This makes them vulnerable and a number of environmental conditions and/or ligands could bring about a decline in the net catalytic activity. An enzyme may be irreversibly killed (inactivation by high temperature, extremes of pH, nonaqueous solvent, chemical modification, etc.) or inhibited by ligands that bind to it. Inhibitors are usually small molecular weight ligands that bring about a decrease in the rate of enzyme-catalyzed reaction. For a molecule to act as an inhibitor, it must physically interact with the enzyme. Interactions with the enzyme that do not affect its catalytic activity (that are kinetically silent!) are of no inhibitory consequence. For example, a molecule may bind to the enzyme without changing any of its kinetic properties. Such ligands may serve as potential baits in enzyme purification but are useless in the study of kinetic mechanisms.