enzymes (enzymes) - a high molecular weight organic compounds of protein nature, the body that perform the role of biological catalysts.
mechanism of action of enzymes
elucidate mechanisms underlying the catalytic action of enzymes is one of the fundamental problems, and not just urgent problems of enzymology, but modern biochemistry and molecular biology.
Long before it became available pure enzymes and has clarified their nature, have become convinced that critical to the implementation of the enzymatic process has a connection with the substrate of the enzyme.Attempts to detect the enzyme complexed with the substrate for a long time did not lead to success, as this complex is labile, it decomposes very quickly.The use of spectroscopy made it possible to identify the enzyme-substrate complexes for catalase, peroxidase, alcohol, flavinzavisimyh enzymes.
method of X-ray analysis yielded a lot of important information on the structure and catalytic mechanisms of action of enzymes.This method was used to establish the connection substrate analogues with enzymes lysozyme and chymotrypsin.
Some direct evidence for the existence of enzyme-substrate complexes managed to get to where one of the stages of the catalytic cycle of the enzyme is bound to the substrate by a covalent bond.An example is the reaction of hydrolysis of n-nitrophenyl acetate catalyzed by chymotrypsin.When mixed with the enzyme chymotrypsin ether is acetylated at the hydroxyl group of the reactive serine residue.This stage is rapid, but atsetilhimotripsina hydrolysis to form acetate and free chymotrypsin is considerably slower.Therefore, in the presence of n-nitrophenylacetate accumulates atsetilhimotripsin that is easily detected.
substrate in presence of the enzyme composition can "catch" by transfer complex unstable EU into an inactive form, for example, by treatment of the enzyme-substrate complex, sodium borohydride, has a strong reducing effect.Such a complex as stable covalent derivative was detected in the enzyme aldolase.It was found that the substrate molecule reacts with e-amino group of lysine.
substrate reacts with the enzyme in a particular part which is called the active center, or core enzyme.Under
active center, or core, realize the enzyme protein moiety which connects to the substrate (cofactors) and causes the enzymatic properties of the molecule.The active site determines the specificity and catalytic activity of the enzyme should be a certain degree of difficulty structure adapted for close approach and interact with the substrate molecule, or its parts directly involved in the reaction.
distinguish among functional groups included in the "catalytically active" portion of the enzyme and forming portion providing a specific affinity (the binding of substrate to the enzyme) - the so-called pin, or "anchor" (or adsorption section of the active site of the enzyme).
mechanism of action of the enzyme theory explains Michaelis-Menten.According to this theory, the process takes place in four stages.
mechanism of action of enzymes: I stage
between the substrate (S) and the enzyme (E) get a connection - formed enzyme-substrate complex of the EU, in which the components are linked by covalent, ionic, water and other bonds.
mechanism of action of enzymes IІ stage
substrate under the influence of the associated enzyme is activated and becomes available to the relevant EU catalysis reactions.
mechanism of action of enzymes IІI stage
catalysis commits the EU.This theory is confirmed by experimental studies.
Finally, IV stage is characterized by the release of the enzyme E and the reaction products R. sequence of transformations can be displayed as follows: E + S - the EU - EU * - E + P.
specificity of enzyme action
Each enzyme acts on a specific substrate, or a group of substances that are similar in structure.The specificity of enzyme action is due to the similarity of the configuration of the active site and the substrate.In the process of interaction formed enzyme-substrate complex.
