Работа нашего организма – чрезвычайно сложный a process that involves millions of cells, thousands of various substances. But there is one area that depends entirely on special proteins, without which human or animal life will be completely impossible. As you probably guessed, we are now talking about enzymes.
Since the basis of these substances arepredominantly proteins, they themselves can be considered them. You need to know that for the first time enzymes were discovered as early as the 30s of the 19th century, only scientists needed more than a century to come to a more or less unified definition for them. So what is the function of protein-enzymes? You will learn about this, as well as their structure and examples of reactions from our article.
You need to understand that not every protein canto be an enzyme even theoretically. Only globular form proteins are able to show catalytic activity towards other organic compounds. Like all natural compounds of this class, enzymes are composed of amino acid residues. Remember that the enzymatic function of proteins (examples of which will be in the article) can be performed only by those of them whose molar mass is not less than 5000.
Энзимы – это катализаторы биологического origin. They have the ability to accelerate reactions due to the closest contact between the two substances involved in the reaction (substrates). It can be said that the enzymatic function of proteins is a process of catalysis of some biochemical reactions, which are characteristic only of a living organism. Only a small part of them can be reproduced in the laboratory.
Note that not all of them come into contact with the substrate.the body of the enzyme, but only its small area, which is called the active center. This is their main property, complementarity. This concept implies that the enzyme is ideally suited to the substrate in form and its physicochemical properties. It can be said that the function of protein-enzymes in this case is as follows:
It is these factors that lead to an acceleration of the reaction. Now let's make a comparison between enzymes and inorganic catalysts.
Compare characteristic | Enzymes | Inorganic catalysts |
Acceleration of direct and reverse reactions | The same | The same |
Specificity (complementarity) | Only suitable for a specific type of substance, high specificity | Can be universal, speeding up several similar reactions at once. |
Speed reaction | Increase reaction intensity several million times. | Acceleration hundreds and thousands of times |
Heating reaction | The reaction goes to "no" because of the full or partial denaturation of proteins involved in it. | When heated, most catalytic reactions are accelerated many times |
Как видите, ферментативная функция белков suggests specificity. From myself, we also add that many of these proteins also have species specificity. Simply put, human enzymes are hardly suitable for the guinea pig.
As for the secondary level,belonging to it is determined with the help of additional types of bonds that can occur between these amino acid residues. These bonds are hydrogen, electrostatic, hydrophobic, and Van der Waals interactions. As a result of the tension that these bonds cause, α-helixes, loops and β-strands are formed in different parts of the enzyme.
The tertiary structure appears as a result of havingthat relatively large portions of the polypeptide chain simply fold. The resulting strands are called domains. Finally, the final formation of this structure occurs only after a stable interaction is established between different domains. It should be remembered that the formation of the domains themselves occurs in an order completely independent of each other.
Typically, the polypeptide chain from which theyformed, consists of approximately 150 amino acid residues. When domains interact with each other, a globule is formed. Since the enzymatic function is performed by active centers based on them, the importance of this process should be understood.
The domain itself is different in that betweenamino acid residues in its composition, there are numerous interactions. Their number is much greater than those for the reactions between the domains themselves. Thus, the cavities between them are relatively “vulnerable” to the action of various organic solvents. Their volume is about 20-30 cubic angstroms that fit several water molecules. Different domains often have a completely unique spatial structure, which is associated with the performance of completely different functions.
As a rule, active centers are located strictlybetween domains. Accordingly, each of them plays a very important role in the course of the reaction. Due to this arrangement of domains, considerable flexibility and mobility of this region of the enzyme is found. This is extremely important, since the enzymatic function is performed only by those compounds that can change their spatial position accordingly.
Between the length of the polypeptide bond in the body of the enzyme andso far as complex functions are performed by them, there is a direct connection. The complication of the role is achieved both due to the formation of the active center of the reaction between the two catalytic domains, and due to the formation of completely new domains.
Некоторые белки-ферменты (примеры - лизоцим и glycogen phosphorylase) can vary greatly in size (129 and 842 amino acid residues, respectively), although they 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 their position in space, which ensures greater stability and speed of reaction.
1. Oxidoreductases. The function of enzyme proteins in this case is the stimulation of redox reactions.
2. Transferase. Can transfer between substrates of the following groups:
3. Hydrolases. In this case, the value of the enzymatic function of proteins is the cleavage of the following types of compounds:
4. Liaz. They have the ability to detach groups with the subsequent formation of a double bond. In addition, they can perform the reverse process: the addition of individual groups to double bonds.
5. Isomerase. In this case, the enzymatic function of proteins is to catalyze complex isomeric reactions. The following enzymes belong to this group:
6. Ligases (otherwise known as synthetase). They serve for the cleavage of ATP with the simultaneous formation of certain bonds.
Often the enzyme is protein globularorigin, the active center of which is represented by its own amino acid residues. In all other cases, the center includes a strongly associated prosthetic group or coenzyme (ATP, for example), whose bond is much weaker. The whole catalyst is called the holoenzyme, and its residue, formed after the removal of ATP, is an apoenzyme.
Thus, on this basis, enzymes are divided into the following groups:
Все вещества, которые входят в состав первой groups are widely used in the food industry. All other catalysts require very specific conditions for their activation, and therefore work only in the body or in some laboratory experiments. Thus, the enzymatic function is a very specific reaction, which consists in stimulating (catalysis) of certain types of reactions in strictly defined conditions of the human or animal organism.
It is absolute.In this case, specificity is manifested only for one, strictly defined type of enzyme. So, urease interacts only with urea. With milk lactose, it will not react under any conditions. Here is the function of protein-enzymes in the body.
In addition, absolute group specificity is often found. Как можно понять из названия, в этом случае there is a "susceptibility" strictly to one class of organic substances (esters, including complex, alcohols or aldehydes). So, pepsin, which is one of the main enzymes of the stomach, shows specificity only in relation to hydrolysis of the peptide bond. Alcohol dehydration interacts exclusively with alcohols, and lactic dehydration breaks down nothing but α-hydroxy acids.
It also happens that the enzymatic functioncharacteristic of a particular group of compounds, but under certain conditions, enzymes can act on quite different from its main "goal" of the substance. In this case, the catalyst "to" a particular class of substances, but under certain conditions, it can break down other compounds (not necessarily similar). However, in this case, the reaction will go many times slower.
The ability to trypsin to act is widely known.on peptide bonds, but few people know that this protein, which performs an enzymatic function in the gastrointestinal tract, may well interact with various ester compounds.
Finally, specificity is optical.These enzymes can interact with the broadest list of completely diverse substances, but only under the condition that they have well-defined optical properties. Thus, the enzymatic function of proteins in this case is in many respects similar to the principle of action not of enzymes, but of catalysts of inorganic origin.
In general, the essence of the concentration effect is nothingdoes not differ from that in the inorganic catalysis reaction. In this case, the concentration of the substrate is created in the active center, which is several times higher than the same value for the entire other volume of the solution. At the center of the reaction, the molecules of the substance that should react between themselves are selectively sorted. It is easy to guess that it is this effect that leads to an increase in the rate of a chemical reaction by several orders of magnitude.
When a standard chemical process takes place,it is extremely important which part the interacting molecules will collide with each other. Simply put, the molecules of a substance at the time of a collision must necessarily be strictly oriented relative to each other. Due to the fact that in the active center of the enzyme such a turn is performed in a forced manner, after which all the components involved line up in a certain line, the catalysis reaction is accelerated by approximately three orders of magnitude.
Under the versatility in this caseit is understood the property of all the components of the active center at the same time (or strictly coordinated) to act on the molecule of the "processed" substance. Moreover, it (the molecule) is not only properly fixed in space (see above), but also significantly changes its characteristics. All this together leads to the fact that it becomes much easier for enzymes to act on the substrate in the necessary way.
