The active site z Typically a pocket or groove on the surface of the protein into which the substrate fits. z The specificity of an enzyme – fit between the active site and that of the substrate. z Enzyme changes shape – tighter induced fit, bringing chemical groups in position to catalyze the reaction.The active site z Typically a pocket or groove on the surface of the protein into which the substrate fits. z The specificity of an enzyme – fit between the active site and that of the substrate. z Enzyme changes shape – tighter induced fit, bringing chemical groups in position to catalyze the reaction