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Encyclopedia > Rate of enzyme mediated reactions
Figure 1: Diagram of a catalytic reaction, showing the energy needed at each stage of the reaction. The substrates (A and B) normally need a large amount of energy to reach the transition state, which then reacts to form the end product (AB). The enzyme creates a microenvironment in which A and B can reach the transition state more easily, reducing the amount of energy needed. Since the lower energy state is easier to reach and therefore occurs more frequently, as a result the reaction is more likely to take place, thus improving the reaction speed.
Figure 1: Diagram of a catalytic reaction, showing the energy needed at each stage of the reaction. The substrates (A and B) normally need a large amount of energy to reach the transition state, which then reacts to form the end product (AB). The enzyme creates a microenvironment in which A and B can reach the transition state more easily, reducing the amount of energy needed. Since the lower energy state is easier to reach and therefore occurs more frequently, as a result the reaction is more likely to take place, thus improving the reaction speed.

The rate of enzyme mediated reactions is the rate of chemical reactions mediated by enzymes. Enzymes can increase reaction rate by favoring or enabling a different reaction pathway with a lower activation energy, making it easier for the reaction to occur. (Drawn January 31 2005 by G. Andruk, released under GNU Free Documentation License) Diagram of a catalytic reaction, showing the energy needed at each stage of the reaction. ... (Drawn January 31 2005 by G. Andruk, released under GNU Free Documentation License) Diagram of a catalytic reaction, showing the energy needed at each stage of the reaction. ... A chemical reaction is a process involving one, two or more substances (called reactants), characterized by a chemical change and yielding one or more product(s) which are different from the reactants. ... Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... The reaction rate for a reactant or product in a particular reaction is defined as the amount (in moles or mass units) per unit time per unit volume that is formed or removed. ... The activation energy in chemistry is the energy needed by a system to initiate a particular process. ...

Contents


Factors influencing rate

The overall rate of enzyme mediated reactions depends on many factors including properties of the cellular environment, modifications to the enzyme and inhibition.


Cellular environment

  • Temperature All chemical reactions speed up as temperature is raised. Extremes of temperature can denature an enzyme so that it can no longer function. The temperature at which the enzyme exhibits maximum activity is called the enzyme's temperature. Temperatures around 40-50°C denature most proteins.
  • Substrate concentration
  • Enzyme concentration De novo synthesis (the production of more enzyme molecules) increases catalysis rates.
  • Enzyme activity Enzyme activity is the catalytic effect exerted by an enzyme.
  • pH Extremes of pH can denature an enzyme so that it can no longer function. Many enzymes function optimally in the neutral pH region. There are exceptions; pepsin, a stomach enzyme, functions only in very acidic conditions, and so cannot work in the small intestine.
  • Salt concentration Extremes of salt concentration can inactivate an enzyme.

Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... A chemical reaction is a process involving one, two or more substances (called reactants), characterized by a chemical change and yielding one or more product(s) which are different from the reactants. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... Denaturation is a structural change in biomolecules such as nucleic acids and proteins, usually caused by heat, acids, bases, detergents, or certain chemicals such as urea. ... In biochemistry, a substrate is a molecule which is acted upon by an enzyme. ... Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... In law, the expression trial de novo literally means new trial. It is most often used in certain legal systems that provide for one form of trial, then another if a party remains unsatisfied with the decision. ... Enzyme activity is the catalytic effect exerted by an enzyme. ... The title of this article begins with a capital letter, due to technical limitations of the MediaWiki software. ... The title of this article begins with a capital letter, due to technical limitations of the MediaWiki software. ... Denaturation is a structural change in biomolecules such as nucleic acids and proteins, usually caused by heat, acids, bases, detergents, or certain chemicals such as urea. ... Pepsin is a protease, a digestive enzyme that degrades food proteins in the stomach. ... The stomach (Gaster) In anatomy, the stomach (in ancient Greek στόμαχος) is an organ in the alimentary canal used to digest food. ... Diagram showing the poop shoot In biology the small intestine is the part of the gastrointestinal tract between the stomach and the large intestine (colon). ... In chemistry, salt is a term used for ionic compounds composed of positively charged cations and negatively charged anions, so that the product is neutral and without a net charge. ...

Modifications

Posttranslational modification means the chemical modification of a protein after its translation. ... Phosphorylation is the addition of a phosphate (PO4) group to a protein or a small molecule. ... A cofactor is the following: In mathematics a cofactor is the minor of an element of a square matrix. ... Nicotinamide adenine dinucleotide (NAD+) (Note that the adenonosyl sugar is of the wrong absolute configuration in the diagram: it should have the same configuration as the nicotinamide sugar. ... A fad, also known as a craze, refers to a fashion that becomes popular in a culture (or subcultures) relatively quickly, remains popular, often for a rather brief period, then loses popularity dramatically. ... Categories: Biochemistry stubs | Thiols ... A Vitamin is an organic molecule required by a living organism in minute amounts for normal health. ... Allosteric modulation is the control of a proteins binding site by a modulator molecule that binds to a regulatory site. ... In biochemistry, an enzyme or other protein is allosteric if its activity or efficiency changes in response to the binding of an effector molecule at a so-called allosteric site. ... The EFFector Newsletter is a weekly publication of the Electronic Frontier Foundation (EFF), dedicated to keeping the organization members and subscribers informed of current issues, urging action through Action Alert, and providing a variety of background information and links. ... A binding site is a region on a protein to which specific ligands bind. ... In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles (or coassembles) with other protein molecules to form a multimeric or oligomeric protein. ...

Inhibition

Enzymes reaction rates can be changed by competitive inhibition, non-competitive inhibition, uncompetitive inhibition and mixed inhibition. In Chemistry:A chemical inhibitor is any substance which will prevent any two other substances from reacting due to its presence, often by reacting with one or the other first. ... Non-competitive inhibition is a type of inhibition that reduces the maximum rate of a chemical reaction (Vmax) without changing the apparent binding affinity of the enzyme for the substrate (Km). ... Mixed inhibition refers to a combination of two different types of reversible enzyme inhibition--competitive inhibition and uncompetitive inhibition. ...


Competitive inhibition

Competitive inhibition. A competitive inhibitor binds reversibly to the enzyme, preventing the binding of substrate. On the other hand, binding of substrate prevents binding of the inhibitor, thus substrate and inhibitor compete for the enzyme.
Competitive inhibition. A competitive inhibitor binds reversibly to the enzyme, preventing the binding of substrate. On the other hand, binding of substrate prevents binding of the inhibitor, thus substrate and inhibitor compete for the enzyme.

The inhibitor may bind to the substrate binding site as shown in the figure, thus preventing substrate binding. Alternatively, binding of substrate to a different binding site may change protein conformation in a way that prevents substrate binding, while substrate binding changes protein conformation to prevent inhibitor binding. These two possibilities can not be distinguished by enzyme kinetics (X-ray crystallography would be a suitable method), thus the frequently found statement that competitive kinetics proves inhibitor binding at the substrate site is false. Drawn by G. Andruk January 31 2005 and released under GNU Free Documentation License. ... Drawn by G. Andruk January 31 2005 and released under GNU Free Documentation License. ...


Uncompetitive inhibition

Uncompetitive inhibition occurs when the inhibitor binds only to the enzyme-substrate complex, not to the free enzyme, the EIS complex is catalytically inactive. This mode of inhibition is rare.


Non-competitive inhibition

Non-competitive inhibitors never bind to the active center, but to other parts of the enzyme that can be far away from the substrate binding site. By changing the conformation (the three-dimensional structure) of the enzyme, they disable or enable the ability of the enzyme to turn over its substrate, while substrate binding is still possible (in other words: there is no competition between substrate and inhibitor for the enzyme). The EIS-complex has no catalytic activity. In chemistry, a chemical conformation is the spatial arrangement of atoms in a molecule. ...


Partially competitive inhibition

The mechanism of partially competitive is similar to that of non-competitive inhibition, except that the EIS-complex has catalytic activity, which may be lower or even higher (partially competitive activation) than that of the ES-complex.


Enzyme inactivation

Inactivators bind to the enzyme irreversibly (while binding of inhibitors is per definitionem reversible). Of particular medical importance are suicide inactivators which bind to the enzyme at a substrate binding site and are then turned over into a compound and do not release the site, preventing the substrate from binding. Certain irreversible neurotoxins, for example, have this property, while other, reversible, toxins do not.


Kinetics

Enzyme kinetics is referred to as Henri-Michaelis-Menten kinetics. The Michaelis constant, and the Lineweaver-Burke diagram help to define enzyme kinetics. Michaelis-Menten kinetics describe the rate of enzyme mediated reactions for many enzymes. ... Michaelis-Menten kinetics describe the rate of enzyme mediated reactions for many enzymes. ... In biochemistry, a Lineweaver-Burke diagram (also called a Lineweaver-Burke plot or double reciprocal plot) is a graphical representation of the Lineweaver-Burke equation of enzyme kinetics: where v is the reaction velocity, Km is the Michaelis-Menten constant, vmax is the maximum reaction velocity, and [S] is the...


  Results from FactBites:
 
Article about "Enzyme" in the English Wikipedia on 24-Apr-2004 (1555 words)
An enzyme is a protein, or protein complex, that catalyzes a chemical reaction in an organism.
Enzymes can increase reaction rate by favoring or enabling a different reaction pathway with a lower activation energy, making it easier for the reaction to occur.
Enzymes are usually specific as to the reactions they catalyze and the substrates that are involved in these reactions.
Enzyme kinetics - Wikipedia, the free encyclopedia (4263 words)
Enzyme kinetics is the study of the rates of chemical reactions that are catalysed by enzymes.
Enzyme assays are laboratory procedures that measure the rate of enzyme reactions.
Enzyme intermediates contain substrates A and B or products P and Q. As shown on the right, enzymes with a ping-pong mechanism can exist in two states, E and a chemically modified form of the enzyme E*; this modified enzyme is known as an intermediate.
  More results at FactBites »

 
 

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