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Ribbon diagram of glycosidase with an arrow showing the cleavage of the maltose sugar substrate into two glucose products.
The enzyme glucosidase converts sugar maltose to two glucose sugars. Active site residues in red, maltose substrate in black, and NAD cofactor in yellow. (PDB: 1OBB​)

Enzymes {{#invoke:IPAc-en|main}} are macromolecular biological catalysts. Enzymes accelerate, or catalyze, chemical reactions. The molecules at the beginning of the process are called substrates and the enzyme converts these into different molecules, called products. Almost all metabolic processes in the cell need enzymes in order to occur at rates fast enough to sustain life.<ref name = "Stryer_2002">{{#invoke:citation/CS1|citation |CitationClass=book }}open access publication - free to read</ref>:8.1 The set of enzymes made in a cell determines which metabolic pathways occur in that cell. The study of enzymes is called enzymology.

Enzymes are known to catalyze more than 5,000 biochemical reaction types.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Most enzymes are proteins, although a few are catalytic RNA molecules. Enzymes' specificity comes from their unique three-dimensional structures.

Like all catalysts, enzymes increase the rate of a reaction by lowering its activation energy. Some enzymes can make their conversion of substrate to product occur many millions of times faster. An extreme example is orotidine 5'-phosphate decarboxylase, which allows a reaction that would otherwise take millions of years to occur in milliseconds.<ref name="radzicka">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref name="pmid17889251">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Chemically, enzymes are like any catalyst and are not consumed in chemical reactions, nor do they alter the equilibrium of a reaction. Enzymes differ from most other catalysts by being much more specific. Enzyme activity can be affected by other molecules: inhibitors are molecules that decrease enzyme activity, and activators are molecules that increase activity. Many drugs and poisons are enzyme inhibitors. An enzyme's activity decreases markedly outside its optimal temperature and pH.

Some enzymes are used commercially, for example, in the synthesis of antibiotics. Some household products use enzymes to speed up chemical reactions: enzymes in biological washing powders break down protein, starch or fat stains on clothes, and enzymes in meat tenderizer break down proteins into smaller molecules, making the meat easier to chew.

Enzyme sections
Intro   Etymology and history    Structure    Mechanism   Cofactors  Thermodynamics  Kinetics  Inhibition   Biological function    Naming conventions    Industrial applications    See also    References    Further reading   

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