Enzymes. Enzyme specificity

24.09.2019

Enzymes are proteins that have catalytic properties. In nature, there are both simple and complex enzymes. The former are entirely represented by polypeptide chains and, upon hydrolysis, decompose exclusively into amino acids. Such enzymes (simple proteins) are hydrolytic enzymes, in particular pepsin, trypsin, papain, urease, lysozyme, ribonuclease, phosphatase, etc. Most natural enzymes belong to the class of complex proteins containing, in addition to polypeptide chains, some non-protein component (cofactor ), the presence of which is absolutely essential for catalytic activity. Cofactors can have a different chemical nature and differ in the strength of the bond with the polypeptide chain. The main properties of enzymes as biocatalysts include: 1.High activity. 2. Specificity – the ability to catalyze the transformation of a substrate or one type of bond. High specificity is due to the conformational and electrostatic complementarity between the molecules of the substrate and the enzyme and the unique structural organization of the active center, which consists of a substrate-binding site (responsible for substrate binding) and a catalytic site (responsible for choosing the path of chemical transformation of the substrate). There are such types of specificity: 1) absolute substrate-enzymes act only on 1-n specific substrate. Example, urease, succinateDH. 2) group specificity- the enzyme acts on 1 type of bonds (eg, peptide, ether, glycosidic). Example, lipases, phosphatase, hexokinase. 3) stereospecificity- the enzyme acts on one type of optical isomer and does not act on the other. It is provided with cis- and trans-isomerism. For example, yeast ferments D-glucose, but does not act on L-glucose. 4) catalytic specificity– the enzyme catalyzes the transformation of the attached substrate in one of the possible ways. 3. Thermolability. The higher the T °, the slower the reaction proceeds. (Z-n Van Hoff). For the indicator of the increase in the rate of a chemical reaction, the VanzHoff temperature coefficient Q 10 is used, which indicates an increase in the reaction rate with an increase in T ° by 10 ° C. The optimum temperature for enzymes is 37-40°C, high activity is 50-60°C, above this indicator denaturation occurs, below 20°-inhibition. With inhibition and denaturation, enzymatic activity is greatly reduced. 4. Dependence of enzyme activity on pH. Each enzyme exhibits maximum activity at a certain pH value. This value is called optimal pH (6 to 8 for enzymes). At pH optimum, there is the best spatial and electrostatic complementarity between the enzyme and the substrate, which ensures their binding, the formation of the enzyme-substrate complex, and its further transformation.

The active center f is the region of the enzyme molecule in which the binding and transformation of the substrate occurs. In simple enzymes, the active center is formed by amino acid residues. In the formation of the active center of complex enzymes, not only amino acid residues take part, but also the non-protein part (coenzyme, prostite group). In the active center, a catalytic center is distinguished, which directly enters into chemical interaction with the substrate, and a substrate-binding center, which provides a specific affinity for the substrate and the formation of its complex with the enzyme. The active center is predominantly located in the recess of the protein molecule. The structure of the active center determines the specificity of enzymes - the ability to catalyze the transformation of one substrate (or a group of closely related sub-components) or one type of bond. The substrate-binding site of the active center determines the absolute and group substrate specificity, stereospecificity, the catalytic site determines the specificity of the transformation pathway.

Any impact that leads to a violation of the tertiary structure leads to a distortion or destruction of the structure of the active center and, accordingly, the loss of catalytic properties of enzymes. If it is possible to restore the native three-dimensional structure of the protein-enzyme, then its catalytic activity is also restored.

Active site of enzymes

Parameter name	Meaning
Article subject:	Active site of enzymes
Rubric (thematic category)	House

Properties and mechanism of action of enzymes. Enzyme cofactors

Enzymes, or enzymes - usually protein molecules or RNA molecules (ribozymes) or their complexes, accelerating (catalyzing) chemical reactions in living systems. The reactants in a reaction catalyzed by enzymes are called substrates, and the resulting substances are called products. Enzymes are specific to substrates (ATPase catalyzes the cleavage of ATP only, and phosphorylase kinase phosphorylates only phosphorylase).

Enzymatic activity can be regulated by activators and inhibitors (activators - increase, inhibitors - decrease).

Protein enzymes are synthesized on ribosomes, while RNA is synthesized in the nucleus.

The terms ʼʼenzymeʼʼ and ʼʼenzymeʼʼ have long been used as synonyms (the first is mainly in Russian and German scientific literature, the second - in English and French).

The science of enzymes is usually called enzymology, not fermentology (so as not to confuse the roots of Latin and Greek words).

The activity of enzymes is determined by their three-dimensional structure.

Like all proteins, enzymes are synthesized as a linear chain of amino acids that folds in a certain way. Each amino acid sequence folds in a specific way, and the resulting molecule (protein globule) has unique properties. Several protein chains can be combined into a protein complex. The tertiary structure of proteins is destroyed when heated or exposed to certain chemicals.

The study of the mechanism of a chemical reaction catalyzed by an enzyme, along with the determination of intermediate and final products at different stages of the reaction, implies an accurate knowledge of the geometry of the tertiary structure of the enzyme, the nature of the functional groups of its molecule, which ensure the specificity of action and high catalytic activity on a given substrate, as well as the chemical nature of the site (sections) of an enzyme molecule, which ensures a high rate of the catalytic reaction. Typically, substrate molecules involved in enzymatic reactions are relatively small compared to enzyme molecules. Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, during the formation of enzyme-substrate complexes, only limited fragments of the amino acid sequence of the polypeptide chain enter into direct chemical interaction - ʼʼactive centerʼʼ - a unique combination of amino acid residues in the enzyme molecule͵ providing direct interaction with the substrate molecule and direct participation in the act of catalysis

In the active center, conditionally allocate

catalytic center - directly chemically interacting with the substrate;
binding center (contact or "anchor" site) - providing specific affinity for the substrate and the formation of the enzyme-substrate complex.

To catalyze a reaction, an enzyme must bind to one or more substrates. The protein chain of the enzyme is folded in such a way that a gap, or depression, is formed on the surface of the globule, where the substrates bind. This region is commonly referred to as the substrate binding site. Usually it coincides with the active site of the enzyme or is located near it. Some enzymes also contain binding sites for cofactors or metal ions.

The enzyme binds to the substrate:

cleans the substrate from the water ʼʼfur coatʼʼ
arranges the reacting substrate molecules in space in the manner necessary for the reaction to proceed
prepares for the reaction (for example, polarizes) substrate molecules.

Usually, the attachment of an enzyme to a substrate occurs due to ionic or hydrogen bonds, rarely due to covalent bonds. At the end of the reaction, its product (or products) is separated from the enzyme.

As a result, the enzyme lowers the activation energy of the reaction. This is because in the presence of the enzyme, the reaction takes a different route (in fact, a different reaction occurs), for example:

In the absence of an enzyme:

A+B = AB

In the presence of an enzyme:

A+F = AF
AF+V = AVF
AVF \u003d AV + F

where A, B - substrates, AB - reaction product, F - enzyme.

Enzymes cannot provide energy for endergonic reactions (which require energy) on their own. For this reason, the enzymes that carry out such reactions couple them with exergonic reactions that release more energy. For example, biopolymer synthesis reactions are often coupled with the ATP hydrolysis reaction.

The active centers of some enzymes are characterized by the phenomenon of cooperativity.

The active center of enzymes - the concept and types. Classification and features of the category "Active center of enzymes" 2017, 2018.

Enzymes are macromolecular substances, the molecular weight of which reaches several million. Molecules of substrates that interact with enzymes usually have a much smaller size. Therefore, it is natural to assume that not the entire enzyme molecule as a whole interacts with the substrate, but only some part of it, the so-called “active center” of the enzyme.

The active center of an enzyme is a part of its molecule that directly interacts with substrates and participates in the act of catalysis.

The active center of the enzyme is formed at the level of the tertiary structure. Therefore, during denaturation, when the tertiary structure is disturbed, the enzyme loses its catalytic activity. !

The active center, in turn, consists of:

- catalytic center which carries out the chemical transformation of the substrate;

- substrate center (“anchor” or contact area), which ensures the attachment of the substrate to the enzyme, the formation of the enzyme-substrate complex.

It is not always possible to draw a clear line between the catalytic and substrate centers; in some enzymes, they coincide or overlap.

In addition to the active center, in the enzyme molecule there is a so-called. allosteric center . This is a section of an enzyme molecule, as a result of the addition to which a certain low molecular weight substance ( effector ), the tertiary structure of the enzyme changes. This leads to a change in the configuration of the active site and, consequently, to a change in the activity of the enzyme. This is the phenomenon of allosteric regulation of enzyme activity.

Many enzymes are multimers (or oligomers ), i.e. composed of two or more subunits protomers(similar to the quaternary structure of a protein).

The bonds between subunits are mostly non-covalent. The enzyme exhibits the maximum catalytic activity precisely in the form of a multimer. Dissociation into protomers sharply reduces the activity of the enzyme.

Enzymes - multimers usually contain a clear number of subunits (2-4), i.e. are di- and tetramers. Although hexa- and octamers (6-8) are known, and trimers and pentamers (3-5) are extremely rare.

Multimeric enzymes can be built from the same or different subunits.

If multimeric enzymes are formed from different types of subunits, they can exist as multiple isomers. Multiple forms of an enzyme are called isoenzymes (isoenzymes or isozymes).

For example, an enzyme consists of 4 subunits of types A and B. It can form 5 isomers: AAAA, AAAB, AABB, ABBB, BBBB. These isomeric enzymes are isoenzymes.

Isoenzymes catalyze the same chemical reaction, usually act on the same substrate, but differ in some physicochemical properties (molecular weight, amino acid composition, electrophoretic mobility, etc.), localization in organs and tissues.

A special group of enzymes are the so-called. multimeric complexes. These are systems of enzymes that catalyze the successive stages of the transformation of a substrate. Such systems are characterized by the strength of the bond and the strict spatial organization of enzymes, which ensures the minimum pathway for the passage of the substrate and the maximum rate of its transformation.

An example is a multienzyme complex that performs the oxidative decarboxylation of pyruvic acid. The complex consists of 3 types of enzymes (M.v. = 4,500,000).

End of work -

This topic belongs to:

Lectures on the course: biochemistry peptides, proteins: their structure, properties, significance in the body, research methods. Physico-chemical properties of proteins.10

Federal Agency for Education .. state educational institution of higher professional ..

If you need additional material on this topic, or you did not find what you were looking for, we recommend using the search in our database of works:

What will we do with the received material:

If this material turned out to be useful for you, you can save it to your page on social networks:

All topics in this section:

RNA dna
H3PO4 H3PO4 Ribose Deoxyribose Nitrogenous bases (A, G, C, U) (A, G, C, T) Table 1 shows the composition

Primary structure of rna and dna
The primary structure of RNA and DNA is the same - it is a linear polynucleotide chain in which the nucleotides are interconnected by 3/5 / phosphodiester bonds that form the remainder

Secondary structure of DNA
The secondary structure of DNA is characterized by E. Chargaff's rule (regularity of the quantitative content of nitrogenous bases): 1. DNA has molar fractions of purine and pyrimidino

Tertiary structure of DNA
The tertiary structure of DNA is a helix and supercoil in complex with proteins. DNA can exist in a linear form (in eukaryotic chromosomes) and in a circular form (in prokaryotes and mitochondria). Spiralization

Structure and functions of RNA
Unlike DNA, an RNA molecule consists of a single polynucleotide chain that is coiled onto itself, i.e. forms all sorts of "loops" and "hairpins" due to the interactions of complementary nitrogen

Exchange of nucleic acids and nucleotides in the human body
The metabolism of nucleotides in the body includes the processes of anabolism (biosynthesis of purine - the main and reserve pathway - and pyrimidine nucleotides) and catabolism (decomposition of nucleic acids

Transcription
Transcription - the biosynthesis of RNA molecules on the DNA template, localized in the cell nucleus, goes on constantly, regardless of the cell cycle. Substrates and Energy Sources for Biosynthetics

Protein biosynthesis
Protein biosynthesis (translation) occurs in polysomes and leads to the construction of a polypeptide chain from amino acids (the primary structure of a protein). For the translation process, you need: matrices

transcription regulation. Operon theory
An operon is a section of DNA encoding the structure of one type of protein, containing a regulatory zone that controls the synthesis of these proteins. Regulation of mRNA transcription includes induction

Citric acid cycle - CTC - Krebs cycle
The citric acid cycle is a series of reactions that occur in mitochondria, during which acetyl groups are catabolized (up to 2CO2) and resuscitation is formed.

Krebs cycle regulation
The limiting reaction of the entire Krebs cycle is the citrate synthesis reaction (citrate synthase enzyme). Regulatory enzymes of the Krebs cycle: Pyruvate dehydrogenase (inhibitors: ATP, NADH +

The role of oxygen in metabolism
The human body functions under aerobic conditions: it receives 90% of its energy with the participation of oxygen. Oxygen performs two essential functions in the metabolism of life.

Oxygen toxicity
For the human body, the toxicity of oxygen is due to the toxicity of its active forms, which can be formed during the transfer of electrons from oxidized substrates to oxygen.

Nucleoside triphosphates
The most common high-energy common intermediates are nucleoside triphosphates (NTPs), which can transfer their terminal high-energy

Biological chemistry Lelevich Vladimir Valeryanovich

Active site of the enzyme

The part of the enzyme molecule that specifically interacts with the substrate is called the active site. The active center is a unique combination of amino acid residues in the enzyme molecule, which ensures its direct interaction with the substrate molecule and is directly involved in the act of catalysis. In complex enzymes, the active center also includes a cofactor. In the active center, a catalytic site, which directly enters into chemical interaction with the substrate, and a binding site, which provides specific affinity for the substrate and the formation of its complex with the enzyme, are conditionally distinguished.

Properties of active sites of enzymes:

1. The active center accounts for a relatively small part of the total volume of the enzyme.

2. The active center has the form of a narrow depression or slit in the enzyme globule.

3. The active center is a three-dimensional formation, in the formation of which functional groups of amino acids linearly distant from each other participate.

4. Substrates bind relatively weakly to the active site.

5. The specificity of substrate binding depends on a strictly defined arrangement of atoms and functional groups in the active site.

Some regulatory enzymes have another center called allosteric or regulatory. It is spatially separated from the active site.

An allosteric center is a section of an enzyme molecule with which certain usually low molecular weight substances (allosteric regulators) bind, the molecules of which are not similar in structure to the substrate. Attachment of the regulator to the allosteric center leads to a change in the tertiary and quaternary structure of the enzyme molecule and, accordingly, the conformation of the active center, causing a decrease or increase in enzymatic activity.

From the book Extended Phenotype [Far Influence of the Gene] author Dawkins Clinton Richard

CHAPTER 5 The Active Germline Replicator In 1957, Beezer proved that the "gene" could no longer be regarded as a single, unitary concept. He decomposed it into three hypostases: muton - the minimum unit of mutational changes; recon - the smallest unit

From the book The Newest Book of Facts. Volume 1 [Astronomy and astrophysics. Geography and other earth sciences. Biology and Medicine] author

From the book Pharmaceutical and Food Mafia by Brower Louis

From the book The Newest Book of Facts. Volume 1. Astronomy and astrophysics. Geography and other earth sciences. Biology and medicine author Kondrashov Anatoly Pavlovich

Center for Pharmacological Surveillance "Paris, February 4, 1977. The NCPC, established in January 1974, met at the General Assembly on February 2, together with delegates from the National Charters of Physicians and Pharmacists, joined by a group of centers for the control of intoxication and

From the book Reading between the lines of DNA [The second code of our life, or the Book that everyone needs to read] author Shpork Peter

Where is the center of mass of the Earth-Moon system? The center of mass of the Earth-Moon system, the so-called barycenter, is located at a distance of 4672 kilometers from the center of the Earth towards the Moon, that is, at a depth of approximately 1700 kilometers below the Earth's surface. Strictly speaking, by

From the book The Secret of God and the Science of the Brain [Neurobiology of Faith and Religious Experience] by Newberg Andrew

What is the pleasure center and where is it located in the body? One of the parts of the brain is the hypothalamus, which is a part of the diencephalon and located under the visual tubercles (thalamus). The hypothalamus, which houses the autonomic centers

From the book Origin of the Brain author Saveliev Sergey Vyacheslavovich

From Berlin to the center of a future revolution He is not offended when he is mistaken for a student or a doctoral student. And this happens to the 32-year-old geneticist all the time. Alexander Meissner - gray-blue eyes, dark blond carelessly combed hair, three-day stubble - not only young,

From the book In Search of Memory [The Emergence of a New Science of the Human Psyche] author Kandel Eric Richard

The Active Approach The active type of meditation begins not with the intention of clearing the mind of thoughts, but with the desire to direct the utmost focused attention to some thought or some object. So, say, a Buddhist can chant a mantra or look at the glow of a candle or at

From the book What if Lamarck is right? Immunogenetics and evolution author Steele Edward

§ 37. The associative center of the reptile brain Having considered the general plan of the structure of the nervous system, we should separately dwell on the new principles of organization and operation of the brain, first realized in reptiles. The nervous system of archaic amniotes has become a logical development of the structure

From the book Psychopaths. A reliable story about people without pity, without conscience, without remorse by Keel Kent A.

From the author's book

Breeding center: somatic hypermutation of rearranged V(D)J genes All available evidence suggests that only rearranged V(D)J genes coding for the antibody protein are mutated in B lymphocytes. In other words, variable genes that remain in the germline configuration

From the author's book

Mendota Juvenile Rehabilitation Center In the early 1990s, a real epidemic of teenage violence swept the United States. The number of crimes committed by juveniles nearly doubled between 1980 and 1993. It seemed like nothing could stop this