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An enzyme (/ˈɛnzaɪm/) 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.
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).