Enzymes chemical reactions involved

In a biocatalytic biosensor the molecular recognition component is an enzyme. Enzymes, macromolecular catalysts that are manufactured by plants and animals, affect the rates of biochemical reactions. Virtually all of the millions of chemical reactions involved in Hfe processes have associated enzymes controlling the rates. CoUectively, there are several thousand enzymes known and perhaps many thousand more yet to be discovered. 

Acid and base catalysis of a chemical reaction involves the assistance by acid or base of a particular proton-transfer step in the reaction. Many enzyme catalysed reactions involve proton transfer from an oxygen or nitrogen centre at some stage in the mechanism, and often the role of the enzyme is to facilitate a proton transfer by acid or base catalysis. Proton transfer at one site in the substrate assists formation and/or rupture of chemical bonds at another site in the substrate. To understand these complex processes, it is necessary to understand the individual proton-transfer steps. The fundamental theory of simple proton transfers between oxygen and nitrogen acids and... 

Enzymes are classified under six main headings, which relate to the chemical reactions involved. Each class is then subdivided in order to classify the other features of the reaction. The main headings are listed below but further details may be found in the Appendix. 

Figure 15.3 Superposition of free energy profiles for wild-type (E) and mutant (E ) enzymes. The reaction involves the formation of an ES complex followed by a transition state for a chemical step, ES, and then the formation of an enzyme-bound intermediate El. Note that the free enzymes are arbitrarily assigned the same free energy. This is valid for comparing the changes in interaction energies at different stages of the reaction (see Chapter 3, section L3, and A. R. Fersht, A. Matouschek, and L.Serrano, J. Molec. Biol. 224,771 (1992)).

Because of its vital character to life as we know it, photosynthesis has been investigated intensively and the general features of the process are now rather well understood. The principal deficiencies in our knowledge include just how the light absorbed by the plants is converted to chemical energy and the details of how the many complex enzyme-induced reactions involved take place. 

Enzyme-catalyzed reactions involve specific, rapid combination of substrate and enzyme to form a complex that is rapidly converted to products through transition states that are controlled by the enzyme s environment. Since enzymes are homogeneous chemical catalysts, we expect them to operate by routes that parallel some of the same processes in reactions that do not involve enzymes. The relative magnitude of enzymic and nonenzymic catalytic parameters has been called catalytic proficiency by Wolfenden6,17 24 and this has been a subject of intense current interest.7,25 32 Wolfenden noted that while nonenzymic reactions have diverse rates, enzyme-catalyzed processes are highly evolved to be comparable in rate, no matter how slow their nonenzymic counterparts. 

Hydrolysis A chemical reaction involving the reaction of a compound with water. Acid hydrolysis usually involves dilute hydrochloric acid, and enzyme hydrolysis involves enzymes such as amylase. 

Acetyl-CoA is oxidized to C02 by the Krebs cycle, also called the tricarboxylic acid cycle or citric acid cycle. The origin of the acetyl-CoA may be pyruvate, fatty acids, amino acids, or the ketone bodies. The Krebs cycle may be considered the terminal oxidative pathway for all foodstuffs. It operates in the mitochondria, its enzymes being located in their matrices. Succinate dehydrogenase is located on the inner mitochondrial membrane and is part of the oxidative phosphorylation enzyme system as well (Chapter 17). The chemical reactions involved are summarized in Figure 18.7. The overall reaction from pyruvate can be represented by Equation (18.5) ... 

When chemical reaction involves more than one apolar solute, short-range hydrophobic association may be important in determining the rate and products of reaction. For example, hydrophobic association between apolar reagent and apolar substrate can enhance the rate of reaction in water (Cayley and Margerum, 1974). Similarly, hydrophobic interactions between enzyme and substrate are important in enzyme catalysed interactions (Jencks, 1969). The role of hydrophobic association in these reactions has been studied using model systems. For example, aminolysis of 8-quinolyl octa-noate by octylamine or decylamine is faster than predicted on the basis of the behaviour of lower amines, the rate enhancement being... 

In order to gain a quantitative understanding of the catalytic power of enzymes, it is essential to be able to calculate the free-energy profiles for enzymatic reactions and the corresponding reference solution reactions. The common prescription of obtaining potential surfaces for chemical reactions involves the use of quantum mechanical (QM) computational approaches, and such approaches have become quite effective in treating small molecules in the gas phase (e.g., Ref. 5). However, here we are interested in chemical reactions in very large systems, which cannot be explored... 

Some enzymatic reactions can be followed directly, either by substrate depletion or product accumulation measurements, with adequate precision for direct enzymatic assays. However, many enzymes catalyze reactions involving species that are not themselves readily measured. In these situations, products are converted to species that are measurable, in a coupled, or indicator reaction. The indicator reaction may be chemical or enzymatic, and quantitatively converts the product of the primary reaction into a readily measurable species. The main requirement for the indicator reaction, whether it is chemical or enzymatic in nature, is that the conversion of the primary product into the measured product must be rapid and quantitative. 

To conclude, the mechanisms by which neurotransmitters pass on their message involve changes in molecular shape rather than chemical reactions. These changes in shape will ultimately lead to some sort of chemical reaction involving enzymes. This topic is covered more fully in Appendix 3. 

Enzymes are proteins employed by Mother Nature to catalyze the chemical reactions necessary to sustain life in plants and animals. As catalysts, enzymes may influence the rates and/or the directions of chemical reactions involving an enormous range of substrates (reactants). Enzymes function by combining with substrates to form enzyme-substrate complexes (reaction intermediates) that subsequently react further to yield products while regenerating the free enzyme. 

Molecular dynamics with periodic boundary conditions is presently the most widely used approach for studying the equilibrium and dynamic properties of pure bulk solvent,97 as well as solvated systems. However, periodic boundary conditions have their limitations. They introduce errors in the time development of equilibrium properties for times greater than that required for a sound wave to traverse the central cell. This is because the periodicity of information flow across the boundaries interferes with the time development of other processes. The velocity of sound through water at a density of 1 g/cm3 and 300 K is 15 A/ps for a cubic cell with a dimension of 45 A, the cycle time is only 3 ps and the time development of all properties beyond this time may be affected. Also, conventional periodic boundary methods are of less use for studies of chemical reactions involving enzyme and substrate molecules because there is no means for such a system to relax back to thermal equilibrium. This is not the case when alternative ensembles of the constant-temperature variety are employed. However, in these models it is not clear that the somewhat arbitrary coupling to a constant temperature heat bath does not influence the rate of reequilibration from a thermally perturbed... 

All chemical reactions involve the conversion of starting materials (called substrates) into products. Catalysts are molecules that make reactions go much faster than they would on their own. By definition, catalysts are facilitators—they themselves are not used up in the reaction and can be re-used. In industrial reactions—say, the manufacture of ammonia—catalysts can be a mix of simple molecules such as iron, potassium, oxygen, and aluminum. Your body s catalysts are enzymes. Some enzymes make the reactions taking place in your body occur up to a trillion times faster than they would without any help Enzymes are therefore essential to life, since your body cannot afford to wait days, weeks, or years to receive the important products of biochemical reactions. 

In flow-based analytical procedures where the chemical reactions involved and/or the steps of analyte separation/concentration are relatively slow, the analytical signal can be attenuated by reducing the mean available time for the development of these physico-chemical processes. From a practical point of view, the result is equivalent to in-line analyte dilution. This possibility has been exploited in the spectrophotometric determination of hydrogen peroxide in contact lens care solutions using a sequential injection lab-on-valve system [60]. In view of the high sensitivity of the reaction between the analyte and 2,2,-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) in the presence of the enzyme... 

Water content in white tea is very important, because it can affect the activities of enzymes and chemical reactions involved. During withering, water vaporizes, and the rate of water evaporation is related to the humidity and temperature. Table 3.1 shows that 50% of water can be lost after 30 hours of withering, while only 10% water is lost after 10 hours of withering. ... 

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