Enzyme Catalysis
Enzymes are protein molecules present in the living system. Their molecular masses range from 104 to 106 g/mol. They are highly efficient biological catalysts which catalyse the reactions taking place in the living cells and also help in controlling the reaction rates.
The reaction in enzyme catalysis occurs at a specific site on the protein molecule. This is called the active site. The reactants in an enzyme reaction are referred to as substrates.
A few examples of enzyme-catalysed laboratory reactions are given below:
The names of the enzymes are written in red color on the arrows.
| Enzymes, their source and the enzymatic reaction | ||
|---|---|---|
| Enzyme | Source | Enzymatic Reaction |
| Invertase | Yeast | Sucrose → Glucose + Fructose |
| Zymase | Yeast | Glucose → Ethyl alcohol + Carbon dioxide |
| Diastase | Malt | Starch → Maltose |
| Maltase | Yeast | Maltose → Glucose |
| Unease | Soyabean | Urea → Ammonia + Carbon dioxide |
| Pepsin | Stomach | Protein → Amino acids |
Characteristics of Enzymes
Enzymes possess certain characteristics which are different from other types of catalysts. A few of these are briefly described below:
1. They are highly specific in their catalytic action for example, urease, even in very low concentrations, catalyses the hydrolysis of urea but it has no detectable effect on the hydrolysis rate of substituted ureas such as methyl urea. There are many such examples to quote. However, there are some exceptions to this generalisation.
2. They are highly sensitive to the acidity or basicity of the solution. It is found that the enzymes show a sharp change in activity if the pH of the solution is changed.
3. Their efficiency is very high, i.e., many of them are so powerful catalysts that they increase the rate of a reaction by many orders of magnitude even at quite low concentration.
4. They are highly sensitive to temperature. The activity of an enzyme is usually found to be maximum at the normal temperature of the organism in which the enzyme is found. Above this temperature, usually the activity is first found to increase temporarily and then drops to zero when the protein is denatured.
5. Their activity increases in the presence of activators and co-enzymes. Presence of certain substance called co-enzymes increases enzymatic activity. When a small non-protein (vitamin) is present along with an enzyme, the catalytic activity is considerably increased.
Activators are generally metal ions such as Na+, Mn2+, Cu2+, etc. These metal ions, when bonded to enzyme molecules, increase their catalytic activity.
6. Inhibitors and poisons affect the activity. The inhibitors or poisons interact with the active functional group or the enzyme surface and result into reduction of catalytic activity of the enzyme. Drugs act as enzyme inhibitors in the body.
Also read Mechanism of Enzyme Reactions (Michaelis-Menten Equation)Source: Physical Chemistry By R.L.Madan