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Enzyme

Historical Development and Classification: – Enzymes discovered in 1833 by Anselme Payen. – Introduction of the term ‘enzyme’ by Wilhelm Kühne in 1877. – Classification […]

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Historical Development and Classification:
– Enzymes discovered in 1833 by Anselme Payen.
– Introduction of the term ‘enzyme’ by Wilhelm Kühne in 1877.
– Classification based on amino acid sequence or enzymatic activity.
– Naming convention using EC numbers by the International Union of Biochemistry and Molecular Biology.
– Broad classification into categories like Oxidoreductases and Transferases.

Enzyme Functionality and Catalysis:
– Enzymes act as biological catalysts by accelerating chemical reactions.
– Specificity determined by the unique three-dimensional structure.
– Enzymes catalyze over 5,000 biochemical reaction types.
– Enzymes do not alter the equilibrium of a reaction and are not consumed.
– Enzyme activity influenced by inhibitors, activators, temperature, and pH.

Enzyme Structure and Mechanism:
– Enzymes are globular proteins with amino acid sequences determining structure and catalytic activity.
– Denaturation occurs when exposed to heat or denaturants, leading to loss of activity.
– Lock and key model and induced fit model explain enzyme specificity.
– Enzymes bind substrates through complementary binding pockets.
– Enzymes accelerate reactions by lowering activation energy through various mechanisms.

Substrate Binding and Catalysis:
– Enzymes have specific binding pockets for substrates based on shape, charge, and hydrophilic/hydrophobic characteristics.
– Proofreading mechanisms in enzymes result in low error rates.
– Enzymes orient substrates to reduce reaction entropy change.
– Enzymes stabilize the transition state, provide alternative reaction pathways, and destabilize the substrate ground state.
– Enzymes may use stabilizing charge distribution, covalent intermediates, and substrate orientation for catalysis.

Regulation and Cofactors:
– Allosteric modulation involves molecules binding to allosteric sites causing conformational changes.
– Enzymes can be inhibited or activated through allosteric interactions.
– Some enzymes require cofactors like inorganic ions or organic compounds for full activity.
– Coenzymes are small organic molecules that transport chemical groups between enzymes.
– Enzymes do not alter the chemical equilibrium of reactions but increase reaction rates by lowering activation energy.

Enzyme (Wikipedia)

Enzymes (/ˈɛnzmz/) are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps. The study of enzymes is called enzymology and the field of pseudoenzyme analysis recognizes that during evolution, some enzymes have lost the ability to carry out biological catalysis, which is often reflected in their amino acid sequences and unusual 'pseudocatalytic' properties.

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

Enzymes are known to catalyze more than 5,000 biochemical reaction types. Other biocatalysts are catalytic RNA molecules, called ribozymes. An enzyme's specificity comes from its unique three-dimensional structure.

IUPAC definition for enzymes

Like all catalysts, enzymes increase the reaction rate 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. 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 therapeutic drugs and poisons are enzyme inhibitors. An enzyme's activity decreases markedly outside its optimal temperature and pH, and many enzymes are (permanently) denatured when exposed to excessive heat, losing their structure and catalytic properties.

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.

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