Do enzymes change to become products or substrates in a chemical reaction?
Enzymes are polypeptide (protein) catalysts, which by defintion are not supposed to be changed at all by the products or reactants at the completion of the reaction. During catalysis, they may assume an intermediate condition where they are chemically or physically altered, but again at the completion of the reaction, they must be unaltered if they remain active. Not all enzymes survive their reactions however. Mono-oxygenases typically form free radicals as part of the reaction, and these are unstable by nature. Often the reactant or product within the active site of the enzyme becomes irreversibly coupled (covalently bonded) to the enzyme, rendering the enzyme inactive with loss of the formation of product too (although the loss of the enzyme is the more significant event). Such enzymes may only go as few as 10 or 100 catalytic cycles.
