enzym

An enzyme is a biological catalyst that accelerates chemical reactions in living organisms. Most enzymes are proteins, though RNA molecules also have catalytic properties (ribozymes). Enzymes are highly specific for their substrates and typically act by lowering the activation energy of a reaction, so they increase the reaction rate without being consumed in the process.

Enzymes have an active site where substrates bind. The binding often induces conformational changes that bring reactive groups into alignment. Catalysis occurs via several mechanisms, including acid-base catalysis, covalent catalysis, and metal ion catalysis. Enzymes are categorized into six main classes by the Enzyme Commission (EC) system: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases. Many enzymes require cofactors, such as metal ions or organic molecules called coenzymes, to be active. Some enzymes are apoenzymes that require a cofactor, while holoenzymes are fully active enzymes with cofactors.

Enzyme activity is influenced by temperature, pH, and substrate concentration, and extreme conditions can denature proteins. Inhibitors can regulate activity; competitive inhibitors block the active site, while noncompetitive inhibitors affect other parts of the enzyme. Allosteric regulation and covalent modification also control activity in living cells. Enzymes play essential roles in digestion, metabolism, DNA replication and repair, and signaling. They have broad applications in industry and medicine, including pharmaceutical synthesis, food processing, and diagnostic assays.

In some languages the term is spelled enzym.