Enzymes are proteins Proteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by the sequence of a gene, which is encoded that catalyze Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive (i.e., increase the rates The reaction rate or rate of reaction for a reactant or product in a particular reaction is intuitively defined as how fast a reaction takes place. For example, the oxidation of iron under the atmosphere is a slow reaction which can take many years, but the combustion of butane in a fire is a reaction that takes place in fractions of a second of) chemical reactions A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about only after the input of some type of energy, viz. heat, light or electricity. Classically, chemical reactions encompass.^[1][2] In enzymatic reactions, the molecules A molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense. In organic chemistry and biochemistry, the term molecule is used less strictly and also is applied to charged organic molecules at the beginning of the process are called substrates In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or more products, which are then released from the, and the enzyme converts them into different molecules, called the products In biochemistry, a product is something "manufactured" by an enzyme from its substrate. For example the products of Lactase are Galactose and Glucose, which are produced from the substrate Lactose. Almost all processes in a biological cell The cell is the functional basic unit of life. It was discovered by Robert Hooke and is the functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular . Other organisms, such as humans, need enzymes to occur at significant rates. Since enzymes are selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways In biochemistry, metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function properly. Because of the many chemicals that may be involved, occur in that cell.

Like all catalysts, enzymes work by lowering the activation energy In chemistry, activation energy is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined as the energy that must be overcome in order for a chemical reaction to occur. Activation energy may also be defined as the minimum energy required to start a chemical reaction. The activation energy of a reaction is usually (E_a^‡) for a reaction, thus dramatically increasing the rate of the reaction. Most enzyme reaction rates are millions of times faster than those of comparable un-catalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium In a chemical process, chemical equilibrium is the state in which the chemical activities or concentrations of the reactants and products have no net change over time. Usually, this would be the state that results when the forward chemical process proceeds at the same rate as their reverse reaction. The reaction rates of the forward and reverse of these reactions. However, enzymes do differ from most other catalysts by being much more specific. Enzymes are known to catalyze about 4,000 biochemical reactions.^[3] A few RNA Ribonucleic acid is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate. RNA is very similar to DNA, but differs in a few important structural details: in the cell, RNA is usually single-stranded, while DNA is usually double- molecules called ribozymes A ribozyme is an RNA molecule possessing a well defined tertiary structure that enables it to catalyze a chemical reaction. Many natural ribozymes catalyze either the hydrolysis of one of their own phosphodiester bonds, or the hydrolysis of bonds in other RNAs, but they have also been found to catalyze the aminotransferase activity of the ribosome also catalyze reactions, with an important example being some parts of the ribosome Ribosomes are the components of cells that make proteins from amino acids. One of the central tenets of biology, often referred to as the "central dogma," is that DNA is used to make RNA, which, in turn, is used to make protein. The DNA sequence in genes is copied into a messenger RNA . Ribosomes then read the information in this RNA and.^[4][5] Synthetic molecules called artificial enzymes Enzyme catalysis of chemical reactions occur with high selectivity and rate in a small part of the enzyme macromolecule known as the active site. There, the binding of a substrate close to functional groups in the enzyme causes catalysis by so-called proximity effects. It is therefore possible to create similar catalysts from small molecule mimics also display enzyme-like catalysis.^[6]

Enzyme activity can be affected by other molecules. Inhibitors Enzyme inhibitors are molecules that bind to enzymes and decrease their activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. They are also used as herbicides and pesticides. Not all molecules that bind to enzymes are inhibitors; enzyme activators bind to enzymes and are molecules that decrease enzyme activity; activators Enzyme activators are molecules that bind to enzymes and increase their activity. These molecules are often involved in the allosteric regulation of enzymes in the control of metabolism. An example of an enzyme activator working in this way is fructose 2,6-bisphosphate, which activates phosphofructokinase 1 and increases the rate of glycolysis in are molecules that increase activity. Many drugs A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage and poisons In the context of biology, poisons are substances that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism. Legally and in hazardous chemical labeling, poisons are especially toxic substances; less toxic substances are labeled " are enzyme inhibitors. Activity is also affected by temperature Historically, two equivalent concepts of temperature have developed, the thermodynamic description and a microscopic explanation based on statistical physics. Since thermodynamics deals entirely with macroscopic measurements, the thermodynamic definition of temperature, first stated by Lord Kelvin, is stated entirely in empirical, measurable, chemical environment (e.g., pH In chemistry, pH is a measure of the acidity or basicity of a solution. It approximates but is not equal to p[H], the negative logarithm of the molar concentration of dissolved hydronium ions (H3O+); a low pH indicates a high concentration of hydronium ions, while a high pH indicates a low concentration. Crudely, this negative of the logarithm), and the concentration In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent of substrate. Some enzymes are used commercially, for example, in the synthesis of antibiotics In common usage, an antibiotic is a substance or compound that kills bacteria or inhibits their growth. Antibiotics belong to the broader group of antimicrobial compounds, used to treat infections caused by microorganisms, including fungi and protozoa. In addition, some household products use enzymes to speed up biochemical reactions (e.g., enzymes in biological washing powders Laundry detergent, or washing powder, is a substance which is a type of detergent that is added when one is washing laundry to aid in getting the laundry cleaner break down protein or fat Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure and composition. Although the words "oils", "fats", stains on clothes; enzymes in meat tenderizers A meat tenderizer refers to either a kitchen utensil or a chemical used for tenderizing meat. Enzymes are used as chemical meat tenderizers break down proteins, making the meat easier to chew).

Etymology and history

As early as the late 18th and early 19th centuries, the digestion of meat Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat, but it may also describe other edible tissues such as organs, livers, skin, brains, bone marrow, kidneys, or lungs. The word meat is also used by the meat packing industry in a more restrictive sense—the flesh of mammalian species raised and by stomach secretions^[7] and the conversion of starch Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store. It is the most important carbohydrate in the human diet and is contained in such staple foods as potatoes, wheat, maize , rice, and cassava to sugars Sugar is an informal term for a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose characterized by a sweet flavor. In food, sugar almost exclusively refers to sucrose, which primarily comes from sugar cane and sugar beet. Other sugars are used in industrial food preparation, but are usually known by more specific by plant extracts and saliva Saliva is the watery and usually frothy substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. Saliva is produced in and secreted from one of the three salivary glands. Human saliva is composed of 98% water, while the other 2% consists of other compounds such as electrolytes, mucus, antibacterial were known. However, the mechanism by which this occurred had not been identified.^[8]

In the 19th century, when studying the fermentation Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. A more restricted definition of fermentation is the chemical conversion of sugars into ethanol. The science of fermentation is known as zymology of sugar to alcohol In chemistry, an alcohol is any organic compound in which a hydroxyl functional group (-O by yeast Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with the 1,500 species currently described estimated to be only 1% of all yeast species. Most reproduce asexually by budding, although a few do so by binary fission. Yeasts are unicellular, although some species with yeast forms may become multicellular through the formation of, Louis Pasteur Louis Pasteur was a French chemist and microbiologist born in Dole. He is remembered for his remarkable breakthroughs in the causes and preventions of disease. His discoveries reduced mortality from puerperal fever, and he created the first vaccine for rabies and anthrax. His experiments supported the germ theory of disease. He was best known to came to the conclusion that this fermentation was catalyzed by a vital force contained within the yeast cells called "ferments Where vitalism explicitly invokes a vital principle, that element is often referred to as the "vital spark," "energy" or "élan vital", which some equate with the "soul"", which were thought to function only within living organisms. He wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells."^[9]

In 1877, German physiologist Wilhelm Kühne Wilhelm Friedrich Kühne was a German physiologist. Born in Hamburg, he is best known today for coining the word enzyme (1837–1900) first used the term enzyme, which comes from Greek Greek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical ancient Greek literature and the New Testament of ενζυμον, "in leaven", to describe this process.^[10] The word enzyme was used later to refer to nonliving substances such as pepsin Pepsin is an enzyme whose precursor form is released by the chief cells in the stomach and that degrades food proteins into peptides. It was discovered in 1836 by Theodor Schwann who also coined its name from the Greek word pepsis, meaning digestion (peptein: to digest). It was the first animal enzyme to be discovered, and, in 1929, it became one, and the word ferment was used to refer to chemical activity produced by living organisms.

In 1897, Eduard Buchner Eduard Buchner was a German chemist and zymologist, awarded with the 1907 Nobel Prize in Chemistry thanks to his work on fermentation submitted his first paper on the ability of yeast extracts that lacked any living yeast cells to ferment sugar. In a series of experiments at the University of Berlin The Humboldt University of Berlin is Berlin's oldest university, founded in 1810 as the University of Berlin (Universität zu Berlin) by the liberal Prussian educational reformer and linguist Wilhelm von Humboldt, whose university model has strongly influenced other European and Western universities. From 1828 it was known as the Frederick William, he found that the sugar was fermented even when there were no living yeast cells in the mixture.^[11] He named the enzyme that brought about the fermentation of sucrose "zymase Zymase is an enzyme complex that catalyzes the fermentation of sugar into ethanol and carbon dioxide. As the conversion takes place, the reaction will gradually slow down. They occur naturally in yeasts. See alcohol dehydrogenase".^[12] In 1907, he received the Nobel Prize in Chemistry The Nobel Prize in Chemistry is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in chemistry, physics, literature, peace, and physiology or medicine. This award is "for his biochemical research and his discovery of cell-free fermentation". Following Buchner's example, enzymes are usually named according to the reaction they carry out. Typically, to generate the name of an enzyme, the suffix -ase The suffix -ase is used in biochemistry to form names of enzymes. The most common way to name enzymes is to add this suffix onto the end of the substrate, e.g. an enzyme that breaks down peroxides may be called peroxidase; the enzyme that produces telomeres is called telomerase. Sometimes enzymes are named for the function they perform, rather is added to the name of its substrate In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or more products, which are then released from the (e.g., lactase Lactase , a part of the β-galactosidase family of enzymes, is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers. Lactase is present predominantly along the brush border membrane of the differentiated enterocytes lining the villi of the small intestine. In humans, lactase is the enzyme that cleaves lactose Lactose is a sugar that is found most notably in milk. Lactose makes up around 2~8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from lac, the Latin word for milk, plus the -ose ending used to name sugars. It has a formula of C12H22O11) or the type of reaction (e.g., DNA polymerase A DNA polymerase is an enzyme that catalyzes the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best-known for their role in DNA replication, in which the polymerase "reads" an intact DNA strand as a and uses it to synthesize the new strand. This process copies a piece of DNA. The newly-polymerized molecule forms DNA polymers).^[13]

Having shown that enzymes could function outside a living cell, the next step was to determine their biochemical nature. Many early workers noted that enzymatic activity was associated with proteins, but several scientists (such as Nobel laureate Richard Willstätter Richard Martin Willstätter was a German organic chemist whose study of the structure of plant pigments, chlorophyll included, won him the 1915 Nobel Prize for Chemistry. Willstätter invented paper chromatography independently of Mikhail Tsvet) argued that proteins were merely carriers for the true enzymes and that proteins per se were incapable of catalysis. However, in 1926, James B. Sumner James Batcheller Sumner was an American chemist. He shared the Nobel Prize in Chemistry in 1946 with John Howard Northrop and Wendell Meredith Stanley showed that the enzyme urease was a pure protein and crystallized it; Sumner did likewise for the enzyme catalase in 1937. The conclusion that pure proteins can be enzymes was definitively proved by Northrop and Stanley, who worked on the digestive enzymes pepsin (1930), trypsin and chymotrypsin. These three scientists were awarded the 1946 Nobel Prize in Chemistry.^[14]

This discovery that enzymes could be crystallized eventually allowed their structures to be solved by x-ray crystallography. This was first done for lysozyme, an enzyme found in tears, saliva and egg whites that digests the coating of some bacteria; the structure was solved by a group led by David Chilton Phillips and published in 1965.^[15] This high-resolution structure of lysozyme marked the beginning of the field of structural biology and the effort to understand how enzymes work at an atomic level of detail.

Structures and mechanisms

Enzymes are generally globular proteins and range from just 62 amino acid residues in size, for the monomer of 4-oxalocrotonate tautomerase,^[16] to over 2,500 residues in the animal fatty acid synthase.^[17] A small number of RNA-based biological catalysts exist, with the most common being the ribosome; these are referred to as either RNA-enzymes or ribozymes. The activities of enzymes are determined by their three-dimensional structure.^[18] However, although structure does determine function, predicting a novel enzyme's activity just from its structure is a very difficult problem that has not yet been solved.^[19]

Most enzymes are much larger than the substrates they act on, and only a small portion of the enzyme (around 3–4 amino acids) is directly involved in catalysis.^[20] The region that contains these catalytic residues, binds the substrate, and then carries out the reaction is known as the active site. Enzymes can also contain sites that bind cofactors, which are needed for catalysis. Some enzymes also have binding sites for small molecules, which are often direct or indirect products or substrates of the reaction catalyzed. This binding can serve to increase or decrease the enzyme's activity, providing a means for feedback regulation.

Like all proteins, enzymes are long, linear chains of amino acids that fold to produce a three-dimensional product. Each unique amino acid sequence produces a specific structure, which has unique properties. Individual protein chains may sometimes group together to form a protein complex. Most enzymes can be denatured—that is, unfolded and inactivated—by heating or chemical denaturants, which disrupt the three-dimensional structure of the protein. Depending on the enzyme, denaturation may be reversible or irreversible.

Structures of enzymes in complex with substrates or substrate analogs during a reaction may be obtained using Time resolved crystallography methods.

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