write down the mechanism of enzyme action? 6  |
Enzymes are very specific and it's was suggested by Fischer that this was because the enzyme has a particular shape into which substrate fits properly. This is often referred as lock and key hypothesis.
1. According to these model the safe of the active site of an enzyme is complementary to the shape of substrate. i.e, the substrate is like a key whose shape is complementary to the enzyme which is supposed to be lock and they fil perfectly.
2. Enzyme catalyzed only those substrate which fit perfectly on the active site of the enzyme
3. Most enzyme are larger then the substrate molecule . The active site is usually a very small portion of the enzyme , 3-12 amino acid. The remaining amino acids which make the bulk of the enzyme, function to maintain the correct globular shape of the enzyme.
4. Once the product is formed , they no longer fit into the active site and escape into surrounding medium.
5. According to the lock and key model enzyme behaves as rigid molecule , however most enzyme are globular and flexible.
The lock and key model of enzyme action was further modified by Henri as enzyme substrate complex theory . He suggest they:-
1. Substrate molecule fit into the active sites located on the surface of the enzyme like one particular key fit into one particular type of lock.
2. Then the enzyme combines with the substrate and form an unstable intermediate compound termed as enzyme substrate complex.
3. This intermediate immediately breaks down into the reaction product and the enzyme.
E + S = ES -- E+ P
Induced fit model: in 1959 koshland suggest a modification to the lock and key hypothesis which is known as induced key hypothesis.
Working from evidence then suggested that some enzymes and their activity sides are more flexible. To these he proposed that the active side can modified it's shape as the substrate interact with enzyme.
The amino acid which make up the active side are moulded into precise shape which enable the enzyme to perform it's catalytic function most efficiently.