work of our body - an extremely complicated process, which involved millions of cells, thousands of different substances.But there is one area that is entirely dependent on the specific proteins, without which the life of a human or animal would be completely impossible.As you probably guessed, we are talking about enzymes.
Today we will consider the enzymatic function of proteins.This is a major area of biochemistry.
Since These materials are preferably proteins, they may themselves be considered them.You should know that for the first time enzymes were discovered in the 30s of the 19th century, only the scientists took more than a century, in order to arrive at a more or less uniform definition for them.So what function is performed by proteins are enzymes?On this, as well as their structure and reactions of the examples you will learn from this article.
have to understand that not every protein can be an enzyme, even in theory.Only globular shaped proteins can exhibit catalytic activity with respect to other organic compounds.As all of this class of natural compounds, enzymes are composed of amino acid residues.Remember that the enzymatic function of proteins (examples of which will be in the paper) can be performed only by those whose molar mass of not less than 5000.
What enzyme modern definition
Enzymes - are catalysts of biological origin.They have the ability to accelerate the reaction by close contact between the two of the reactants (substrates).We can say that the enzymatic function of proteins - a process some catalysis of biochemical reactions that are specific to a living organism.Only a small part of them can be reproduced in a laboratory.
should be noted that in recent years in this area there has been some breakthrough.Scientists gradually comes close to creating artificial enzymes that can be used not only for the economy but also medicine.Enzymes are being developed that can effectively destroy even small areas starting cancer.
Which parts of the enzyme directly involved in the reaction?
Note that in contact with the substrate is not included the entire body of the enzyme, but only a small portion, which is the active center.This is their main feature, complementarity.This concept assumes that the enzyme substrate is ideal in shape and its physicochemical properties.It can be said that the function of enzymes in this case, is the following:
- their water comes down from the surface of the shell.
- There is a certain deformation (polarization, for example).
- after which they are arranged in a special way in the space, while approaching each other.
These factors lead to an acceleration of the reaction.And now let's make a comparison between the enzymes and inorganic catalysts.
| comparison between | Enzymes | inorganic catalysts |
| acceleration of the forward and reverse reactions | Equal | Equal |
| specificity (complementarity) | only suitable to a certain type of substances, high specificity | may be universal, accelerating several similar reactions |
| reaction rate | increases the intensity of the reaction of a few million times | Accelerationhundreds and thousands of times |
| Reaction to heat | reaction goes to "no" because of the total or partial denaturation of the participating proteins | When heated, most catalytic reactions repeatedly accelerated |
As you can see, the enzymatic function of proteins involves specificity.From myself I will also add that many of these proteins have also species specific.Simply put, the human enzyme is hardly suited for the guinea pig.
Important information on the structure of enzymes
The structure of these compounds is isolated just three levels.The primary structure can be identified by the amino acid residues that are part of the enzymes.Since the enzymatic function of proteins, examples of which we have repeatedly cited in this article may be exercised only certain categories of compounds, to identify them precisely on this basis is quite real.
As for the secondary level, belonging to it is determined by means of additional types of relationships that may arise between the amino acid residues.This communication hydrogen, electrostatic, hydrophobic, and van der Waals interactions.As a result of the tension that cause these connections in different parts of the enzyme produced α-helix, the loop and β-strands.
tertiary structure is a result of the fact that a relatively large portions of the polypeptide chain is simply collapsed.The resulting strands are called domains.Finally, the final formation of this structure takes place only after established between different domains sustained interaction.It should be remembered that the formation of the domains takes place in a completely independent manner from each other.Some characteristics
domains
Typically, the polypeptide chain from which they are formed, consists of approximately 150 amino acid residues.When domains interact with each other, formed a globule.Since the function is performed by the enzymatic active centers based on them, should be aware of the importance of this process.
domain itself is characterized in that between amino acid residues in its structure there are numerous interactions.Their number is much greater than that for the reaction between the domains themselves.Thus, the cavity between the relatively "vulnerable" for the action of various organic solvents.The volume of the order of 20-30 cubic Angstroms, which fits some of the water molecules.Different domains are likely to have a completely unique three-dimensional structure, which is associated with the performance of entirely different functions.
active centers
As a rule, the active sites are located strictly between domains.Accordingly, each of which plays a very important role in the course of the reaction.As a result of this arrangement of domains found considerable flexibility, mobility in the area of the enzyme.This is extremely important, since the enzymatic function is performed only those compounds that can suitably change its spatial position.
connection between the length of the polypeptide in the body of the enzyme, and by how complex functions they performed, there is a direct link.The increasing complexity of the role is achieved both through the formation of the active center of the reaction between the catalytic domain and due to the formation of entirely new domains.
Some enzyme proteins (examples - lysozyme and glycogen phosphorylase) can vary greatly in size (129 and 842 amino acid residues, respectively), though catalyze the cleavage reaction of the same types of chemical bonds.The difference is that more massive and large enzymes are able to better control its position in space, which ensures greater stability and speed of response.
main classification of enzymes
Currently, common and widespread throughout the world is a standard classification.According to her, it stands six major classes, with the relevant subclasses.We consider only the basic.Here they are:
1. Oxidoreductases.The function of enzymes in this case - stimulation of redox reactions.
2. Transferases.May make transfers between the substrates of the following groups:
- -carbon residues.
- Remains of aldehydes and ketones.
- acyl and glycosyl components.
- Alkyl (as an exception, can not tolerate CH3) residues.
- nitrogen bases.
- Groups containing phosphorus.
3. hydrolases.In this case, the enzymatic function of proteins is the cleavage of the following types of compounds:
- ester.
- glycosides.
- esters and thioesters.
- Relations peptide type.
- bonds of CN (except of the same peptide).
4. Lyases.They have the ability to group disengages with subsequent formation of a double bond.Furthermore, there may perform the inverse process: joining selected groups to double bonds.
5. Isomerases.In this case, the enzymatic function of proteins is complicated isomeric catalysis reactions.This group includes the following enzymes:
- racemase, epimerase.
- Tsistransizomerazy.
- intramolecular oxidoreductases.
- intramolecular transferases.
- intramolecular lyase.
6. Ligases (otherwise known as synthetase).They are used for splitting of ATP while forming some connections.
easy to see that the enzymatic function of proteins is incredibly important, as they are in some degree of control over virtually all reactions taking place every second in your body.
What remains of the enzyme after the interaction with the substrate?
often globular protein is an enzyme origin, the active center of which is represented by its amino acid residues.In all other cases, the center includes strongly associated with him prosthetic group or coenzyme (ATP, for example), the connection is much weaker.A catalyst called a holoenzyme, and its residue, after removal of the formed ATP apoenzyme.
Thus, on this basis enzymes are divided into the following groups:
- Simple hydrolase, lyase, and isomerase, which generally do not contain coenzyme base.
- enzyme protein (examples - some transaminase) comprising a prosthetic group (lipoic acid, for example).This group includes many of peroxidase.
- Enizmy, which required regeneration of the coenzyme.They include a kinase, as well as most of the oxidoreductases.
- Other catalysts, the composition of which is not yet fully understood.
All substances, which are part of the first group, are widely used in the food industry.All other catalysts require very special conditions for its activation, and therefore work only in the body or in some laboratory tests.Thus, enzymatic functions - it is a very specific reaction, which consists in stimulating (catalysis) reactions in certain types of well-defined conditions of a human or an animal.
What happens in the active site, or why enzymes work so effectively?
We have repeatedly said that the key to understanding of enzymatic catalysis is the creation of the active center.It's going on the specific binding of the substrate, which in these circumstances is much more active react.In order for you to understand the complexity of the reactions carried out there, give a simple example: glucose fermentation to occur, you must immediately enzymes 12!Equally difficult interaction is made possible only because of the fact that a protein that performs the function of the enzyme, has the highest degree of specificity.
Species specificity enzymes
It is absolute.In this case, the specificity is shown only one strictly definite type enzyme.Thus, urease reacts only with urea.Lactose milk in the reaction, it does not enter under any circumstances.That is what function the proteins perform enzymes in the body.
In addition, the group is not uncommon absolute specificity. As the name implies, in this case there is "sensitivity" strictly to a class of organic compounds (esters, including complex alcohols or aldehydes).Thus, pepsin, which is one of the key enzymes of the stomach, only exhibits specificity for hydrolysis of the peptide bond.Alkogoldegidraza interacts exclusively with alcohols and laktikodegidraza not split anything but α-hydroxy acids.
It happens also that the enzymatic function characteristic of a particular group of compounds, but under certain conditions, the enzymes can act on quite different from its main "target" of a substance.In this case, the catalyst "tends" to a certain class of substances, but under certain conditions it can cleave and other compound (not necessarily equivalent).However, in this case, the reaction will proceed much more slowly.
trypsin widely known ability to act on peptide bonds, but very few people know that this protein that performs the enzymatic function in the gastrointestinal tract, may be reacted with a variety of ester compounds.
Finally, the specificity is optical.These enzymes can interact with a wide variety of substances list entirely, but only under the condition that they have a well-defined optical properties.Thus, the enzymatic function of proteins in this case is very similar to the principle of action of an enzyme, the inorganic catalysts.
What factors determine the efficiency of catalysis?
Today, it is believed that factors that determine an extremely high degree of efficiency of enzymes are:
- effect concentration.
- Effect of spatial orientation.
- versatility of the active site of the reaction.
In general, the essence of the concentration effect is no different from that in the reaction of inorganic catalysis.In this case, the active center created such a concentration of the substrate, which is several times higher than the same value for all other volumes.In the center of the reaction selectively sorted molecules substance to react together.It is not difficult to guess that this effect leads to increased chemical reaction rate by several orders of magnitude.
When a standard chemical process takes place, it is extremely important, which part of the interacting molecules will collide with each other.Simply stated, the molecules of the substance in the moment of collision must be strictly orientated with respect to each other.Due to the fact that the active site of the enzyme such reversal is performed forcibly, whereupon all components involved are arranged in a certain line, the catalysis reaction is accelerated by about three orders of magnitude.
Under the multi-functionality in this case refers to the property of all the components of the active site at the same time (or strongly agreed) to act on the molecule "being processed" substance.Here it (the molecule) is not only properly fixed in space (see. Above), but also greatly changes its characteristics.All this together results in the fact that the enzyme becomes much easier to act on the substrate as needed.
