Enzyme catalysts or enzymes as a catalyst are biocatalysts that can be utilised in the transformation of organic compounds. A natural enzyme is generally a biological macromolecule that is produced by living organisms. Basically, these are complex nitrogenous proteins that help to catalyse the biochemical reactions in living organisms. More significantly, all biochemical reactions occurring in living organisms depend on catalysts.
There are also enzymes that have been more or less isolated and are employed in biocatalysis or enzyme catalysis. With the help of modern biotechnology, non-natural enzymes are also produced in labs today. With such developments, the modified enzymes are widely used to catalyze novel small molecule transformations that may be difficult to achieve using classical synthetic organic chemistry. When natural or modified enzymes are used to perform certain organic synthesis, it is known as chemoenzymatic synthesis. The reactions that are performed using the enzyme are classified as chemoenzymatic reactions.
Table of Content
- Characteristics of Enzyme Catalyst
- Enzyme Activators
- Enzyme Inhibitors
- Enzyme Catalysis
- Mechanism of Enzyme Catalysis
- Frequently Asked Questions
All in all, enzyme catalysts usually increase the rate of chemical reactions, which further result in the conversion of substrate into a product. There are mainly two types of enzyme catalysts – activation enzymes and inhibitory enzymes. We will learn more about them in the following paragraphs.
Characteristics of an Enzyme Catalyst
In comparison to inorganic catalysts which include metals, acids and bases, enzymes are very particular when it comes to reactions. A certain type of enzyme can react with only one particular compound or its substrate. As far as the mechanism is concerned, when enzymes act as catalysts, they tend to weaken the substrate bonds, thereby lowering the overall activation energy. Reactions take place and the product is formed. A single enzyme molecule can be used repeatedly to transform several substrate molecules. Lets us also quickly go through some of the important characteristics of an enzyme catalyst below.
1. Specificity of Enzymes
Enzymes are highly specific in nature. This specific nature is of the following types:
(a) Group-specific: These enzymes will act on molecules having a specific functional group like amines, acids, etc. Enzymes are not only structural specific but also specific to the chemical groups surrounding them.
Example: Pepsin hydrolyses a peptide bond in which the amino group (NH2 group) is contributed by an aromatic amino acid such as phenylalanine, tryptophan.
(b) Linkage-specific: In this type, the activity of the enzyme depends upon the linkage of enzyme molecules with functional groups.
(c) Bond-specific: Enzymes are specific to the substrate having a similar bond and similar structure.
Example: α-amylase enzyme can hydrolyse α-1-4 glycosidic bond in glycogen and starch. Here, enzyme is specific to the α-1-4 glycosidic bond and not to the substrate.
(d) Substrate-specific: Enzyme specific for one substrate and one reaction.
Example: Maltase acts only on maltose.
(e) Optical-specific: Enzymes are specific to the optical configuration of the substrate.
Example: L-amino acid oxidase acts only on L-amino acids.
(f) Geometrical-specific: Enzymes can act on a different substrate having the same molecular geometry.
Example: Alcohol dehydrogenase can oxidize both ethanol and methanol to give corresponding aldehydes.
2. Optimum Temperature
High-temperature causes the deactivation of enzymes. So, most enzymes function effectively at an optimum temperature of 25 – 35°C.
Certain substances increase enzyme activity to a very high or enormous rate. This activation exists as a molecule that is bound to an allosteric site of enzymes which “increase” the activation centre on the enzyme.
1. Hexokinase (I) acts as an activator to extract the glucose in the glycolysis pathway.
2. Glucokinase is an enzyme activator that combines with enzymes released by pancreatic cells used in the treatment of diabetes.
A certain molecule binds the active site of an enzyme and decreases its activity, which are known as enzyme inhibitors. These may be drugs, pathogens, pesticides. A drug acts as an enzyme inhibitor and attacks the active site.
Example: Hydrolysis of cane sugar
Sugarcane is sucrose (C12H22O11), which basically is a dextro rotator with a specific angle of rotation +62.5. In the process, enzyme invertase sucrose undergoes hydrolysis to give α – D(+) glucose and β – D(-) fructose as products. The solutes contain more leave rotatory fructose whose angle of the specific rotator is -92.2. Hence, this mixture is known as invert sugar and the process is the inversion of cane sugar.
Sucrose α-D(+)Glucose α-D(-)fructose
+62.5 (+52.4) (-92.2)
This conversion of Dextro rotators sucrose to fructose is done by enzyme and block the attack of substrate, which are known as competitive inhibitors.
5. Optimum pH
pH is a very important characteristic feature of biochemical reactions. Higher pH reactions generally deactivate the enzyme activity, and lower pH media encourages the growth of microbes. So, optimum pH conditions are required for enzyme catalysis. Generally, pH from 7.2 to 7.4 is required for the enzymatic reactions.
Also Read: pH Scale and Acidity
6. Activation Centre
Enzymes are biological catalysis with a greater number of activation centres and large surface area. They are more efficient than inorganic catalysis due to more activation centre enzymes are enzyme catalysis.
Example 1: Hydrolysis of starch.
Starch is a complex polysaccharide, which is present in potato, rice and other grains. It contains α – D(+) glucose with C1 – C4 glycosidic linkage, diastase enzyme hydrolysis the complex polysaccharide starch into simple monosaccharide glucose.
Example 2: Ethyl alcohol production
Ethanol is obtained from glucose by the enzymatic action, glucose is converted into ethyl alcohol and CO2 by the enzyme catalysis of zymase enzyme produced from yeast.
The above reaction belongs to enzyme catalysis.
Example 2: Hydrolysis of urea
Urea is an excretory chemical produced in the metabolic reactions of a living organism. It undergoes hydrolysis to give ammonia and CO2. Due to the offensive smell of NH3 public toilets are often with bad smell. This hydrolysis is catalysed by the enzymatic action of the urease enzyme.
When there is an increase in the rate of a chemical process by a biological molecule typically an enzyme, the process is known as enzyme catalysis. Such processes involve chemical reactions and the catalysis generally occurs at a localized site known as the active site.
Mechanism of Enzyme Catalysis
The mechanisms of enzyme catalysis usually vary in different processes. However, they are quite similar in principle to other types of chemical catalysis. There is a reduction of energy barrier(s), therefore, separating the reactants from the products. With reduced activation energy the fraction of reactant molecules that can overcome this barrier increases and the product is formed.
An important factor that we need to consider is that enzymes can catalyze reactions in both directions but cannot take a reaction forward nor change the equilibrium position. The enzyme is not changed or consumed during the reaction and it can perform many catalyses repeatedly.
Meanwhile, the most common mechanism that explains the activity of enzymatic catalysis is the lock and key mechanism.
Also Read: Ziegler-Natta Catalyst
Important concepts of lock and key mechanism:
- This mechanism exactly explains the action of an enzyme.
- The enzyme surface is exactly like a key.
- Its surface has so many active centres with many fructose groups.
- Substrate molecule has a shape exactly like a lock, this enzyme fits into the substrate molecule where the exchange of functional groups takes place.
- This leads to the formation of an enzyme-substrate complex which transforms into an enzyme product complex.
- This enzyme product complex dissociates into enzymes and products.
Chemoenzymatic Synthesis and its Advantages
We have already stated what is chemoenzymatic synthesis above. Below we will look at some of the advantages of this process.
- The enzymes that are used are environmentally benign. Meaning they are completely degraded in the environment.
- Enzymes can react under mild or biological conditions. Due to this problems of undesired side-reactions such as decomposition, isomerization, racemization and rearrangement are greatly minimized.
- Enzymes that are used in chemoenzymatic synthesis can be immobilized on a solid support. Such enzymes have high stability and re-usability. They can be used to conduct reactions in continuous mode in microreactors.
- Enzymes can be easily modified to enable non-natural reactivity and this can result in a broader substrate range, enhanced reaction rate or catalyst turnover.
Frequently Asked Questions On Enzyme Catalyst
1. What is the role of enzyme inhibitors in enzyme catalysis?
Enzyme inhibitors are mainly chemical substances, bacteria, and pathogens or pesticide molecules. These attack the activation site of the enzyme in two ways. Some molecules act as competitive inhibitors, and other molecules attack the allosteric site and stop the action of the enzyme decreasing its activity.
2. What are the optimum temperature and pH for the action of an enzyme?
At high-temperature enzymes are deactivated and their action is retarded. Similarly, at a very low temperature, they are activated. The optimum temperature required for the action of the enzyme is 25 – 55°C while the optimum pH for the enzymatic action is 7.2 – 7.4.
3. What are the common metal ions which act as enzyme activators?
Some transition metal ions such as Cu+2, Fe+2, Mn+2, Mo+2 act as a prosthetic factor of the enzymes. These increase the enzymatic catalysis and their activity.
4. What is the inversion of cane sugar?
In the catalytic action of the enzyme invertase, the highly dextrorotatory sucrose on hydrolysis gives a mixture of glucone and leaves rotating sucrose which is in more percentage in the mixture. This is known as the inversion of cane sugar mixture of α – D(+) glucose and fructose.
5. Why do public toilets give offensive bad odour?
The excretory material urea is hydrolysed to form ammonia by the enzymatic action of urease, and also due to interference of oxygen and moisture in the atmosphere which gives a bad odour.