Enzymes Action – An enzyme is a three dimensional globular protein that has specific chemical composition due to its component amino acids and a specific shape. Every enzyme by virtue of its specificity recognizes and reacts with a special chemical substance called substrate. Any enzyme, therefore, reacts only with its specific substrate and transforms it into products(s). it is then released unaltered and thus can be used again and again.
In certain cases enzymes act in a series of chemical reactions in a particular order to complete a metabolic pathway such as respiration or photosynthesis. The successive enzymes containing these reactions are normally present together in a precise order of reaction such that substrate molecules can be literally handed on’ from one enzyme to another forming an enzyme toenzyme chain. In this way. The products from one step in pathway are transferred to the enzyme catalyzing the next step. Fig. 3.2Enzyme to enzyme chain (association) |
An enzyme and its substrate react with each other through a definite charge-bearing site of an enzyme called active site. The charge and shape of the active site of the enzyme. These amino acids are brought closer and are arranged in a specific way by coiling and folding of the polypeptide chain within the globular symmetry of the enzyme (fig. 3.3).
Fig. 3.3:diagrammatic representation of an enzyme-substrate reaction (lock and key Model)
The active site of the enzyme is made up of two definite regions i.e the binding site and the catalytic site. The binding site helps the enzyme in the recognition and site and the catalytic site. The binding site helps the enzyme in the recognition and binding of a proper substrate to produce an ES complex. This reaction activates the catalytic site. Activated catalytic site catalyzes the transformation of the substrate into product (s). Thus the enzyme after catalysis detaches itself from the products unchanged.
| Most enzymes do not float about in a kind of cytoplasmic ‘soup’ but are attached to membranes systems inside the cell in specific and orderly arrangements. Mitochondria and chloroplasts. Are good examples of this. |
Lmil Fischer (1890) proposed a lock and Key model to visualize substrate and enzyme interaction. According to this model, as one specific key can open only a specific lock, in the same manner a specific enzyme can transform only one substrate into products(s).
According to lock and key model the active site is a rigid structure. There is no modification or flexibility in the active site before. During or after the enzyme action and it is used only as a template. Later studies did not support this model in all reactions.
On the basis of new evidences Koshland (1059) proposed its modified form. This is known as induce fit Model. He argued that when a substrate combines with an enzyme, it induces changes in the enzyme structure. The change in structure enables the enzyme to perform its catalytic activity more effectively.