Enzyme specificity refers to the tendency for enzymes to catalyze a specific set of chemical reactions. As explained by the Worthington Biochemical Corporation, some enzymes are absolutely specific and only catalyze one chemical reaction. Other enzymes exhibit group specificity and only act on molecules with given functional groups, such as amino groups. Linkage specific enzymes act on particular bonds, while stereochemical specific enzymes operate on steric or optical isomers.
According to a 2010 study published in the Encyclopedia of Life Sciences, specificity arises by virtue of the three dimensional structure of the site at which the enzyme binds with the target substrate. In this way, enzymes only bond with a given range of chemical reactions. Some enzymes include a secondary structure that fits the chemical substrate and functions as a proofreader, which further ensures enzyme specificity. Some enzymes that catalyze a variety of chemical substrates perform differently depending on the substrate with which they bond. For example, when an enzyme bonds with a preferred substrate, the enzyme may conform to the substrate more completely than it would if it bonded with a non-preferred substrate.
The 2010 Encyclopedia of Life Sciences study explains that specificity is not always absolute. From time to time, new enzymes evolve from interactions with alternative chemical reactions.