Enzyme

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​)

An enzyme (/ˈɛnzm/) is a protein that acts as a biological catalyst, accelerating chemical reactions without being consumed in the process. The molecules on which enzymes act are called substrates, which are converted into products. Nearly all metabolic processes within a cell depend on enzyme catalysis to occur at biologically relevant rates.[1]: 8.1  Metabolic pathways are typically composed of a series of enzyme-catalyzed steps. The study of enzymes is known as enzymology, and a related field focuses on pseudoenzymes—proteins that have lost catalytic activity but may retain regulatory or scaffolding functions, often indicated by alterations in their amino acid sequences or unusual 'pseudocatalytic' behavior.[2][3]

Enzymes are known to catalyze over 5,000 types of biochemical reactions.[4] Other biological catalysts include catalytic RNA molecules, or ribozymes, which are sometimes classified as enzymes despite being composed of RNA rather than protein. More recently, biomolecular condensates have been recognized as a third category of biocatalysts, capable of catalyzing reactions by creating interfaces and gradients—such as ionic gradients—that drive biochemical processes, even when their component proteins are not intrinsically catalytic.[5]

Enzymes increase the reaction rate by lowering a reaction’s activation energy, often by factors of millions. A striking example is orotidine 5'-phosphate decarboxylase, which accelerates a reaction that would otherwise take millions of years to occur in milliseconds.[6][7] Like all catalysts, enzymes do not affect the overall equilibrium of a reaction and are regenerated at the end of each cycle. What distinguishes them is their high specificity, determined by their unique three-dimensional structure, and their sensitivity to factors such as temperature and pH. Enzyme activity can be enhanced by activators or diminished by inhibitors, many of which serve as drugs or poisons. Outside optimal conditions, enzymes may lose their structure through denaturation, leading to loss of function.

Enzymes have widespread practical applications. In industry, they are used to catalyze the production of antibiotics and other complex molecules. In everyday life, enzymes in biological washing powders break down protein, starch, and fat stains, enhancing cleaning performance. Papain and other proteolytic enzymes are used in meat tenderizers to hydrolyze proteins, improving texture and digestibility. Their specificity and efficiency make enzymes indispensable in both biological systems and commercial processes.

IUPAC definition for enzymes
  1. ^ Stryer L, Berg JM, Tymoczko JL (2002). Biochemistry (5th ed.). San Francisco: W.H. Freeman. ISBN 0-7167-4955-6. Archived from the original on 10 December 2010.Open access icon
  2. ^ Murphy JM, Farhan H, Eyers PA (April 2017). "Bio-Zombie: the rise of pseudoenzymes in biology". Biochemical Society Transactions. 45 (2): 537–544. doi:10.1042/bst20160400. PMID 28408493.
  3. ^ Murphy JM, Zhang Q, Young SN, Reese ML, Bailey FP, Eyers PA, et al. (January 2014). "A robust methodology to subclassify pseudokinases based on their nucleotide-binding properties". The Biochemical Journal. 457 (2): 323–334. doi:10.1042/BJ20131174. PMC 5679212. PMID 24107129.
  4. ^ Schomburg I, Chang A, Placzek S, Söhngen C, Rother M, Lang M, et al. (January 2013). "BRENDA in 2013: integrated reactions, kinetic data, enzyme function data, improved disease classification: new options and contents in BRENDA". Nucleic Acids Research. 41 (Database issue): D764 – D772. doi:10.1093/nar/gks1049. PMC 3531171. PMID 23203881.
  5. ^ Philip Ball (21 January 2025). Jen Schwartz (ed.). "Mysterious Blobs Found inside Cells Are Rewriting the Story of How Life Works. Tiny specks called biomolecular condensates are leading to a new understanding of the cell". Scientific American. 332 (2 (February)). Condensates can act as catalysts for biochemical reactions, even if their component proteins do not. This is because condensates create an interface between two phases, which sets up a gradient in concentrations—of ions for example, creating an electric field that can trigger reactions. The researchers have demonstrated condensate-induced catalysis of a wide range of biochemical reactions, including those involving hydrolysis (in which water splits other molecules apart).
  6. ^ Radzicka A, Wolfenden R (January 1995). "A proficient enzyme". Science. 267 (5194): 90–93. Bibcode:1995Sci...267...90R. doi:10.1126/science.7809611. PMID 7809611. S2CID 8145198.
  7. ^ Callahan BP, Miller BG (December 2007). "OMP decarboxylase--An enigma persists". Bioorganic Chemistry. 35 (6): 465–469. doi:10.1016/j.bioorg.2007.07.004. PMID 17889251.

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