Enzymes definitions

Definition of an enzyme Definition of an active it Enzymes are protein catalysts that increase the velocity of a chemical reaction, and are not consumed during the reaction they catalyze. Each enzyme has an active site where the substrate binds and is converted to product. 

Classification Enzyme Definition Mixt. of enzymes that catalyze the hydrolysis of glycosidic linkages of polysaccharides such as glycogen, starch, or their degradation prods. 

CAS 9001-05-2 EINECS/ELINCS 232-577-1 Classification Oxidizing enzyme Definition Enzyme found in animals, plants, bacteria, and fungi... 

CAS 9025-70-1 EINECS/ELINCS 232-803-9 Classification Enzyme Definition From Penicillium lilacinum Uses Natural enzyme for foods treatment in reducing dental caries Regulatory UK, Japan approved Manuf./Distrib. Fluka http //www.sigma-aidrich.com. Sigma... 

In view of the progress in the field of immobilized or insolublized enzymes, definition of the terms employed is required. The term immobilized applies to enzymes etc. which have been reacted with another molecule to give a product of greater molecular size, i.e. the mobility of the enzyme, etc. in solution has been reduced. However, such derivatives may be water soluble or insoluble. By international agreement the use of the term immobilized is recommended rather than use of the original term insolubilized which does not encompass the water-soluble macromolecular derivatives. 

C and T E Klein 1986. Molecular Graphics and QSAR in the Study of Enzyme-Ligand ractions. On the Definition of Bioreceptors. A ccounts of Chemical Research 19 392-400,... 

Litde is known about metaboHc inactivation of ( -endorphin and the dynorphins. NEP, and to a lesser extent APN, are only weaMy active against P-endorphin (183). Enzymes are known which degrade P-endorphin in vitro under nonphysiological conditions (202) or which inactivate P-endorphin by N-acetjlation (203). Alack of specific degradative enzymes for these peptides may account for their relatively long half-life in vivo though this has not been definitively estabUshed. 

Chemical Pathology. Also referred to as clinical chemistry, this monitoring procedure involves the measurement of the concentration of certain materials in the blood, or of certain enzyme activities in semm or plasma. A variety of methods exist that allow (to variable degrees of specificity) the definition of a particular organ or tissue injury, the nature of the injurious process, and the severity of the effect (76). 

Historically, dietary fiber referred to iasoluble plant cell wall material, primarily polysaccharides, not digested by the endogenous enzymes of the human digestive tract. This definition has been extended to iaclude other nondigestible polysaccharides, from plants and other sources, that are iacorporated iato processed foods. Cellulose [9004-34-6] (qv) is fibrous however, lignin [9005-53-2] (qv) and many other polysaccharides ia food do not have fiberlike stmctures (see also Carbohydrates). 

These definitions are valid only when the concentration of the enzyme is very small compared with that of the substrate. Moreover, they apply only to the initial rate of formation of products in other words, the rate of formation of the first few percent of the product, before the substrate has been depleted and products that can interfere with the catalytic reaction have accumulated. 

For biochemical reactions in which hydrogen ions (H ) are consumed or produced, the usual definition of the standard state is awkward. Standard state for the ion is 1 M, which corresponds to pH 0. At this pH, nearly all enzymes would be denatured, and biological reactions could not occur. It makes more sense to use free energies and equilibrium constants determined at pH 7. Biochemists have thus adopted a modified standard state, designated with prime ( ) symbols, as in AG°, AH°, and so on. For values determined... 

In many situations, the actual molar amount of the enzyme is not known. However, its amount can be expressed in terms of the activity observed. The International Commission on Enzymes defines One International Unit of enzyme as the amount that catalyzes the formation of one micromole of product in one minute. (Because enzymes are very sensitive to factors such as pH, temperature, and ionic strength, the conditions of assay must be specified.) Another definition for units of enzyme activity is the katal. One katal is that amount of enzyme catalyzing the conversion of one mole of substrate to product in one second. Thus, one katal equals 6X10 international units. 

Viewed in this way, the best definition of rate enhancement depends upon the relationship between enzyme and substrate concentrations and the enzyme s kinetic parameters. 

Definitive identification of lysine as the modified active-site residue has come from radioisotope-labeling studies. NaBH4 reduction of the aldolase Schiff base intermediate formed from C-labeled dihydroxyacetone-P yields an enzyme covalently labeled with C. Acid hydrolysis of the inactivated enzyme liberates a novel C-labeled amino acid, N -dihydroxypropyl-L-lysine. This is the product anticipated from reduction of the Schiff base formed between a lysine residue and the C-labeled dihydroxy-acetone-P. (The phosphate group is lost during acid hydrolysis of the inactivated enzyme.) The use of C labeling in a case such as this facilitates the separation and identification of the telltale amino acid. 

This definition recognizes that immobilization—e.g., at cellular membranes— is the native state for some enzymes. Although interesting mathematics are... 

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