Enzyme Concentration
Enzyme concentration is directly proportional to enzyme activity. If substrate concentration is maintained at a high level, and other conditions such as pH and temperature are kept constant then with the increase of enzyme concentration the activity of the enzyme will also increase and with the decrease of enzyme concentration, the activity of the enzyme will also decrease.
Usually in natural conditions, the substrate concentration is higher than enzymes. However, when the enzyme concentration becomes saturated as compared to the substrate, then the rate of reaction will not increase further, this maximum rate (Vmax value) is never obtained.
Substrate Concentration:
Like enzymes the substrate concentration is also directly proportional to enzyme activity up to optimum level. If we keep the other conditions such as temperature, pH, and enzyme concentration at a constant state and change the amount of substrate then we find that with an increase in substrate concentration, the reaction rate will increase only up to the optimum level.
This is because more substrate molecules will be colliding with enzyme molecules so more products will be formed. However, at a certain concentration substrate becomes saturated then any further increase will have no effect on the rate of reaction because at this point all the active sites of the enzyme are occupied, the maximum rate.
Energy of Activation(EA):
The minimal amount of energy required to start a chemical reaction is called activation energy. It is denoted by EA and measured in units of kilojoules per mole (KJ/Mol) or kilocalories per mole (Kcal/Mol).
In a non-living system, heat is used as the energy of activation to increase the movement of molecules. However, in living systems heat energy cannot be used because this heat may denature enzymes and proteins of the cell.
There are hundreds of reactions continuously going on in the cell. For all these reactions large amount of activation energy is required. Such a huge amount of energy is not present in living organisms. However, living organisms possess enzymes that lower the activation energy.
In the presence of enzymes less activation energy is required but in the absence of enzymes more activation energy is required to convert a substrate into a product.
3.4 Enzyme Inhibition
The term enzyme inhibition means to stop the enzyme from its expression (functioning), usually by enzyme inhibitors or due to a change in temperature or pH.
Such molecules or substances that stop enzyme activity are called enzyme inhibitors, such as drugs, toxins, products of enzymes, etc.
Some of the poisons are enzyme inhibitors, that's why a person exposed to poison may die. On the other hand, there are enzyme activators that bind to enzymes to increase enzyme activity.
Types of Inhibitors:
Generally, two main types of enzyme inhibitors are irreversible and reversible inhibitors.
Irreversible Inhibitors:
These inhibitors stop enzyme activity permanently either by destroying (denaturing) the active site of the enzyme or occupying the active site by making a covalent bond with the active site.
The irreversible inhibitors often contain reactive functional groups e.g., aldehydes, and alkenes. These electrophilic groups make covalent bonds with amino acid side chains.
Reversible Inhibitors:
Such inhibitors attach to enzymes non-covalent interactions such as hydrogen bonds, hydrophobic interactions, and ionic bonds.
These inhibitors generally do not undergo chemical reactions when bonded to enzymes and are easily removed from enzymes.
Competitive Inhibitors:
Such inhibitors which have a similar shape to the substrate molecule hence compete with the substrate to occupy the active site.
The process of inhibition depends on the concentration of the subject of substance and inhibitors. With high concentrations of inhibitors, the chances of inhibition are also high.
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