E. Enzymes:
Thousands of different chemical reaction take place automatically at a given time in a tiny living cell. The reactions takes place at body temperature. If these enzymes were not present in the cell, either the reactions would not occur or if they occur they would occur at a very very slow rate.
Know your Scientist
German chemist Edward Buchner discovered enzymes by accident. Buchner discovered that living cells were not necessary but that yeast extract could bring about fermentation. He then coined the term Enzyme (Gk. En = in, zyma = yeast i.e. in yeast). This term is now commonly used for all biocatalysts.
Each enzyme catalyzes a small number of reactions, specifically perhaps only one. The substance upon which an enzyme acts is termed as the substrate. The enzymes which act within the cell in which they are synthesized are known as endo-enzymes e.g., enzymes produced in the chloroplast and mitochondria, if they act outside the cell in which they are synthesized, they are known as exo-enzymes e.g., enzymes released by many fungi. These enzymes, synthesised by living cell, retain their catalytic property even when extracted from cells.
Do you know
Rennet tablets used for coagulating milk protein casien (Cheese) contain renin enzyme that is obtained from the stomach of calf.
Nature of Enzymes :
On the basis of chemical composition, enzymes can be put into two categories.
(i) Purely proteinaceous enzymes e.g. proteases that split protein
(ii) Conjugated enzymes are made up of a protein to which a non-protein prosthetic group is attached.
The prosthetic group is firmly bound to the protein component by chemical bonds and is not removed by hydrolysis.
If the prosthetic group is removed the protein part of the enzyme becomes inactive.
There are enzymes which require certain organic compounds and inorganic ions for their activity. The organic compounds that are tightly attached to the protein part are called coenzymes whereas the inorganic ions which are loosely attached to the protein part are called co-factors. Some of the organic co-enzymes are nicotinamide adenine-dinucleotide (NAD) and flavin mononucleotide (FMN). Inorganic ions of metals which act as co-factors include magnesium, copper, zinc, iron, manganese etc.
Iron (Fe :) is a co-factor of enzyme catalase, manganese is a co-factor of peptidases. Often metal co-factors are referred to as enzyme activators.
Properties of Enzymes :
1. Proteinaceous Nature:
All enzymes are basically made up of protein.
2. Three-Dimensional conformation :
All enzymes have specific 3-dimensional conformation. They have one or more active sites to which substrate (reactant) combines. The points of active site where the substrate joins with the enzyme is called substrate binding site.
3. Catalytic Property :
Enzymes are like inorganic catalysts and influence the speed of biochemical reactions but themselves remain unchanged. After completion of the reaction and release of the product they remain active to catalyse again. A small quantity of enzymes can catalyse the transformation of a very large quantity of the substrate into an end product. For example, sucrose can hydrolyse 100000 times of sucrose as compared with its own weight.
4. Specificity of action:
The ability of an enzyme to catalyse one specific reaction and essentially no other is perhaps its most significant property. Each enzyme acts upon a specific substrate or a specific group of substrates.
5. Reversibility of action :
Enzymes are very sensitive to temperature and pH. Each enzyme exhibits its highest activity at a specific pH, called optimum pH. Any increase or decrease in pH causes decline in enzyme activity e.g. enzyme pepsin (secreted in stomach) shows highest activity at an optimum pH of 2 (acidic). Trypsin (in duodenum) is most active at an optimum pH of 9.5 (alkaline). Both these enzymes viz. pepsin and trypsin are protein digesting enzymes.
6. Temperature :
Enzymes are destroyed at higher temperature of 60-70°C or below, they are not destroyed but become inactive. This inactive state is temporary and the enzyme canbecome active at suitable temperature. Most of the enzymes work at an optimum temperature between 20°C and 35°C.
Nomenclature of Enzymes :
There are various ways of naming enzymes. Enzymes are named by adding the suffix-'ase' to the name of the substrate on which they act e.g. protease, sucrose, nuclease etc. which break up proteins, sucrose and nucleic acids respectively.
The enzymes can be named according to the type of function they perform e.g. dehydrogenase remove hydrogen, carboxylase add CO2 decarboxylases removes CO2, oxidases helping in oxidation.
Some enzymes are named according to the source from which they are obtained e.g. papain from papaya, bromelain from the member of Bromeliaceae family, pineapple.
According to international code of enzyme nomenclature, the name of each enzyme ends with an -ase and consists of double name. The first name indicates the nature of substrate upon which the enzyme acts and the second name indicates the reaction catalysed e.g. pyruvic decarboxylase catalyses the removal of CO2, from the substrate pyruvic acid. Similarly, the enzyme glutamate pyruvate transaminase catalyses the transfer of an amino group from the substrate glutamate to another substrate pyruvate.
