Enzyme

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enzyme

 [en´zīm]
any protein that acts as a catalyst, increasing the rate at which a chemical reaction occurs. The human body probably contains about 10,000 different enzymes. At body temperature, very few biochemical reactions proceed at a significant rate without the presence of an enzyme. Like all catalysts, an enzyme does not control the direction of the reaction; it increases the rates of the forward and reverse reactions proportionally.

Enzymes work by binding molecules so that they are held in a particular geometric configuration that allows the reaction to occur. Enzymes are very specific; few molecules closely fit the binding site. Each enzyme catalyzes a specific type of chemical reaction between a few closely related compounds, which are called substrates of the enzyme.

Enzymes are given names ending in -ase. In older names, the suffix is added to the name of the substrate, as in amylase, an enzyme that breaks down the polysaccharide amylose. In newer names, the suffix is added to the type of reaction, as in lactate dehydrogenase, an enzyme that converts lactate to pyruvate by transferring a hydrogen atom to nicotinamide-adenine dinucleotide (NAD).
Regulation of Enzymes. The reaction rate of an enzyme-catalyzed reaction varies with the pH, temperature, and substrate concentration. Under physiologic conditions the rates of many reactions are controlled by substrate concentrations. Certain key reactions are controlled by one of three different mechanisms.

In allosteric regulation, the enzyme can bind molecules, which are referred to as effectors, at a site other than the active site, which is referred to as an allosteric site. In many biochemical pathways the enzyme that catalyzes the first reaction in the pathway is inhibited by the final product of the last reaction, so that when sufficient product is present the whole pathway is shut down. This is an example of negative feedback.

Many enzymes are regulated by phosphorylation. A phosphate group is attached to the enzyme by another enzyme, called a protein kinase. When the enzyme is phosphorylated it changes its shape and thus its activity. Phosphorylation activates some enzymes and inactivates others; by this means one protein kinase can control several enzymes.

All enzymes are controlled by their rate of synthesis. Like all proteins, enzymes are synthesized by ribosomes, which translate the genetic information coded in the deoxyribonucleic acid (DNA) of the chromosomes into the specific amino acid sequence of the enzyme. The expression of many genes is controlled by the processes of genetic regulation. Thus, although each cell contains the information to make all of the body's enzymes, it actually makes only those appropriate for its specific type of cell. The synthesis of some enzymes can be induced or repressed by the action of specific hormones, substrates, or products so that the enzyme is produced only when metabolic conditions require its presence.
Inborn Errors of Metabolism. Hundreds of genetic diseases that result from deficiency of a single enzyme are now known. Many of these diseases fall into two large classes. The aminoacidopathies result from deficiency of an enzyme in the major pathway for the metabolism of a specific amino acid. The amino acid accumulates in the blood, and it or its metabolites are excreted in the urine. The lysosomal storage diseases result from deficiency of a lysosomal enzyme and the accumulation of the substance degraded by that enzyme in lysosomes of cells throughout the body. The stored material is usually a complex substance, such as glycogen, a sphingolipid, or a mucopolysaccharide.ƒ

An example of an aminoacidopathy is phenylketonuria (PKU), which results from a deficiency of the enzyme phenylalanine hydroxylase, which converts the amino acid phenylalanine to tyrosine. Phenylalanine accumulates in the blood and phenylpyruvic acid is excreted in the urine. The phenylalaninemia eventually results in mental retardation due to defective formulation of myelin. However, PKU can be detected at birth by a screening test for phenylalanine in the blood, and clinical symptoms can be avoided by strict adherence to a low-phenylalanine diet.

An example of a lysosomal storage disease is tay-sachs disease, which results from a deficiency of the enzyme hexosaminidase A. The stored substance is a sphingolipid, GM2-ganglioside, which accumulates in nerve tissue, causing blindness and mental deterioration. No cure is possible, but antenatal diagnosis can be made by determining hexosaminidase A activity in fetal fibroblasts from an amniotic fluid specimen drawn by amniocentesis. It is also possible to identify carriers (heterozygotes) who are at risk for having children with the disease.
Enzyme Assays. Several enzymes are important in clinical pathology. Enzymes characteristic of a tissue are released into the blood when the tissue is damaged; hence assays of serum enzyme levels can aid in the diagnosis or monitoring of specific diseases. Lipase and amylase levels are useful in pancreatic diseases; alkaline phosphatase (ALP), lactate dehydrogenase (LD), aspartate transaminase (AST or GOT), and alanine transaminase (ALT or GPT) in liver diseases; and LD and creatine kinase (CK) in myocardial infarction. ALP is also released in bone diseases. Many enzymes have different forms (isoenzymes) in different organs. The isoenzymes can be separated by electrophoresis in order to determine the origin of the enzyme. Isoenzymes of LD, CK, and ALP have the most clinical utility.
See accompanying table.
activating enzyme one that activates a given amino acid by attaching it to the corresponding transfer ribonucleic acid.
brancher enzyme (branching enzyme) α-glucan-branching glycosyltransferase: an enzyme involved in conversion of amylose to amylopectin; deficiency of this enzyme causes amylopectinosis.
constitutive enzyme one produced by a microorganism regardless of the presence or absence of the specific substrate acted upon.
debrancher enzyme (debranching enzyme) dextrin-1,6-glucosidase: an enzyme that acts on glucose residues of the glycogen molecule and is important in glycogenolysis; deficiency of this enzyme causes Forbes' disease.
induced enzyme (inducible enzyme) one whose production requires or is stimulated by a specific small molecule, the inducer, which is the substrate of the enzyme or a compound structurally related to it.
proteolytic enzyme one that catalyzes the hydrolysis of proteins and various split products of proteins, the final product being small peptides and amino acids.
repressible enzyme one whose rate of production is decreased as the concentration of certain metabolites is increased.
respiratory e's enzymes of the mitochondria, e.g., cytochrome oxidase, which serve as catalysts for cellular oxidations.

en·zyme

(en'zīm),
A macromolecule that acts as a catalyst to induce chemical changes in other substances, while itself remaining apparently unchanged by the process. Enzymes, with the exception of those discovered long ago (for example, pepsin, emulsin), are generally named by adding -ase to the name of the substrate on which the enzyme acts (for example, glucosidase), the substance activated (for example, hydrogenase), and/or the type of reaction (for example, oxidoreductase, transferase, hydrolase, lyase, isomerase, ligase or synthetase-these being the six main groups in the Enzyme Nomenclature Recommendations of the International Union of Biochemistry). For individual enzymes not listed below, see the specific name.
Synonym(s): organic catalyst (1)
[G. + L. en, in + zymē, leaven]

enzyme

/en·zyme/ (en´zīm) a protein that catalyzes chemical reactions of other substances without itself being destroyed or altered upon completion of the reactions. Enzymes are divided into six main groups: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases. Symbol E.
allosteric enzyme  one whose catalytic activity is altered by binding of specific ligands at sites other than the substrate binding site.
brancher enzyme , branching enzyme 1,4-α-glucan branching enzyme: an enzyme that catalyzes the creation of branch points in glycogen (in plants, amylopectin); deficiency causes glycogen storage disease type IV.
constitutive enzyme  one produced constantly, irrespective of environmental conditions or demand.
debrancher enzyme , debranching enzyme
2. any enzyme removing branches from macromolecules, usually polysaccharides, by cleaving at branch points.
induced enzyme , inducible enzyme one whose production can be stimulated by another compound, often a substrate or a structurally related molecule.
proteolytic enzyme  peptidase.
repressible enzyme  one whose rate of production is decreased as the concentration of certain metabolites is increased.
respiratory enzyme  one that is part of an electron transport (respiratory) chain.

enzyme

(ĕn′zīm)
n.
Any of numerous compounds that are produced by living organisms and function as biochemical catalysts. Some enzymes are simple proteins, and others consist of a protein linked to one or more nonprotein groups.

en′zy·mat′ic (-zə-măt′ĭk), en·zy′mic (-zī′mĭk, -zĭm′ĭk) adj.
en′zy·mat′i·cal·ly, en·zy′mi·cal·ly adv.

enzyme

[en′zīm]
Etymology: Gk, en, in, zyme, ferment
a protein produced by living cells that catalyzes chemical reactions in organic matter. Most enzymes are produced in tiny quantities and catalyze reactions that take place within the cells. Digestive enzymes, however, are produced in relatively large quantities and act outside the cells in the lumen of the digestive tract. The substance that is acted upon by an enzyme is called a substrate.

enzyme

A protein that catalyzes most chemical reactions in biological systems without itself being destroyed or altered by the reaction; enzymes accelerate the rate of reactions by lowering transition state energy Enzyme Commission groups Oxidoreductase, transferase, hydrolase, lyase, isomerase, ligase.

en·zyme

(en'zīm)
A protein that acts as a catalyst to induce chemical changes in other substances, while remaining apparently unchanged itself by the process. Enzymes, with the exception of those discovered long ago (e.g., pepsin, emulsin), are generally named by adding -ase to the name of the substrate on which the enzyme acts (e.g., glucosidase), the substance activated (e.g., hydrogenase), or the type of reaction (e.g., oxidoreductase, transferase, hydrolase, lyase, isomerase, ligase or synthetase-these being the six main groups in the Enzyme Nomenclature Recommendations of the International Union of Biochemistry).
[G. + L. en, in + zymē, leaven]

enzyme

A biochemical catalyst that enormously accelerates a chemical reaction. Enzymes are complex protein molecules highly specific to particular reactions. Almost everything that happens in the body, at a chemical level, is mediated by one or more of the many thousands of different enzymes in the cells, and much of the length of each DNA molecule consists of codes for enzymes.
Enzymeclick for a larger image
Fig. 149 Enzyme . The effect of pH activity.

enzyme

a protein molecule that catalyses a biochemical reaction by lowering the ACTIVATION ENERGY required for the reaction to proceed. Enzymes are usually specific to particular substrates (see ACTIVE SITE) and are sensitive to environmental conditions such as pH and temperature (see Fig. 149, and Q10 ). ALLOSTERIC ENZYMES exist in inactive and active forms, while others can be inhibited by nonsubstrate molecules (see COMPETITIVE INHIBITION, NONCOMPETITIVE INHIBITION). Protein-splitting enzymes (PROTEASES) are produced in nonactive forms in the mammalian digestive system to minimize the risk of self-digestion. For example, TRYPSIN is produced as inactive trypsinogen.

Enzyme

A substance produced by the body to assist in a chemical reaction. In carbohydrate intolerance, lack of an enzyme makes it impossible for one type of sugar to be broken down into a simpler form so that it can be absorbed by the intestines and used by the body.

enzyme

liquid or globular protein, acting as a catalyst to intracellular reactions; enzymes are all suffixed by -ase; named for the substrate on which it acts (e.g. glucosidase acts on glucose), the substance activated (e.g. hydrogenase, hydrogen activating) or the type of reaction occurring (e.g. oxidoreductase)

enzyme (enˑ·zīm),

n protein that acts as a catalyst during chemical reactions.

enzyme

A protein substance which catalyses (i.e. enhances a chemical reaction in other bodies without undergoing a change in itself) and is formed by living cells but can act independently of their presence. Example: Enzyme preparations (containing pancreatin, papain or subtilisin A) used to break down tear proteins that become attached to the surface of contact lenses. See contact lens deposits; phagocytosis; surfactant; wetting solution.

en·zyme

(en'zīm)
A macromolecule that acts as a catalyst to induce chemical changes in other substances, while itself remaining apparently unchanged by the process.

enzyme (en´zīm),

n a protein substance that acts as a catalyst to speed up metabolic and other processes involving organic materials. Some enzymes function within cells; others function in the extracellular fluids and tissue spaces and organs. They are active in all major tissue functions, such as cellular respiration, muscle contraction, digestive processes, and energy consumption, and are produced intracellularly.
enzyme-linked immunosorbent assay (ELISA),
n a species-specific serologic laboratory procedure used to identify microorganisms infecting or inhabiting a tissue or organ system. Its dental use is in the identification of pathogens involved in periodontal disease.

enzyme

any protein that acts as a catalyst, increasing the rate at which a chemical reaction occurs. The animal body probably contains about 10,000 different enzymes. At body temperature, very few biochemical reactions proceed at a significant rate without the presence of an enzyme. Like all catalysts, an enzyme does not control the direction of the reaction; it increases the rates of the forward and reverse reactions proportionally.

activating enzyme
one that activates a given amino acid by attaching it to the corresponding transfer ribonucleic acid.
enzyme assays
several enzymes are important in clinical pathology. Enzymes characteristic of a tissue are released into the blood when the tissue is damaged, and enzyme levels in the blood can aid in the diagnosis or monitoring of specific diseases. Lipase and amylase levels are useful in pancreatic diseases; alkaline phosphatase (ALP), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in liver diseases; and lactate dehydrogenase (LD), AST and creatine kinase (CK) in muscle disease. ALP is also released in bone diseases. Many enzymes have different forms (isoenzymes) in different organs. The isoenzymes can be separated by electrophoresis in order to determine the origin of the enzyme. Isoenzymes of LD, CK and ALP have the most clinical utility.
brancher enzyme, branching enzyme
amylo-(1,4→1,6)-transglycosylase; important in the synthesis of the branched glycogen molecule. Absence of the enzyme causes an increase in the length of the glucose chains and a decrease in the number of branch points in the glycogen molecules.
congenital enzyme deficiency
in humans hundreds of genetic diseases that result from deficiency of a single enzyme are now known. Many of these diseases fall into two large classes. The aminoacidopathies, e.g. phenylketonuria (PKU), result from deficiency of an enzyme in the major pathway for the metabolism of a specific amino acid. The amino acid accumulates in the blood, and it or its metabolites are excreted in the urine. The lysomal storage diseases, e.g. gangliosidosis, mannosidosis, result from deficiency of a lysomal enzyme and the accumulation of the substance degraded by that enzyme in lysosomes of cells throughout the body. The stored material is usually a complex substance, such as glycogen, a sphingolipid or a mucopolysaccharide. Many similar diseases are now identified in animals and are to be found under the specific name of each disease.
constitutive enzyme
one produced by a microorganism regardless of the presence or absence of the specific substrate acted upon.
core enzyme
the smallest aggregate of an enzyme's subunits that has enzymatic activity.
debrancher enzyme, debranching enzyme
dextrin-1,6-glucosidase: an enzyme that acts to move glucose residues of the glycogen molecule, and is important in glycogenolysis.
induced enzyme, inducible enzyme
one whose production requires or is stimulated by a specific small molecule, the inducer, which is the substrate of the enzyme or a compound structurally related to it.
enzyme induction
the effect some compounds such as phenobarbitone and phenytoin have in increasing the activity of microsomal hepatic enzymes. This may cause alterations in the metabolism of concurrently administered drugs.
microsomal e's
those associated with the endoplasmic reticulum of cells, particularly of the liver.
proteolytic enzyme
one that catalyzes the hydrolysis of proteins and various split products of proteins, the final product being small peptides and amino acids.
repressible enzyme
one whose rate of production is decreased as the concentration of certain metabolites is increased.
respiratory e's
enzymes of the mitochondria, e.g. cytochrome oxidase, which serve as catalysts for cellular oxidations.
restriction e's

Patient discussion about Enzyme

Q. My muscle enzymes are at 355, my DR says normal is 200. She refered me to a Neurologist. What could be wrong? I am experiencing sore legs when I walk, weakness, and sometimes difficulty in swallowing. I am 46 I had a minor heart attack 5 yrs ago with a stent placed in my LAD. I am on Crestor 10mg. my Dr. has adjusted the dosage several times and used other drugs but it doesn't change the results much if at all.

A. Crestor itself may cause elevated muscle enzymes (you probably refer to Creatine Kinase, http://en.wikipedia.org/wiki/Creatine_kinase). However, weakness and swallowing problems may raise the suspicion of a disease of the nerves or muscles.

More discussions about Enzyme
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