Question

The enzyme which has EC number 4.2.1.7 is assigned to which of the following classes of enzyme?
a) Hydrolases
b) Lyases
c) Isomerase
d) Ligase

Answer 1

Lyases are the enzymes which help in breaking of the bonds. They do not involve hydrolysis. It mainly involves oxidation which helps in breaking old bonds and forming new bonds.

Complete answer:
EC number is the numerical classification of enzymes which is based on the chemical reactions they catalyse. All the classes of enzymes have been assigned different EC numbers which are universal. The enzymes are named by adding suffix -ase to the name of the substrate.
There are 6 classes if enzymes and are named accordingly-
1. Oxidoreductase- These are numbered as 1. They bring about oxidation-reduction.
2. Transferase- These are numbered as EC-2. These enzymes help in transferring one functional group to another like aldehydes to ketones.
3. Hydrolases- These enzymes are numbered as EC-3. They bring about hydrolysis.
4. Lysases- These enzymes are named EC-4. They bring about breaking of bonds.
5. Isomerase- These enzymes are named EC-5. They bring about isomerism.
6. Ligase- These enzymes are named EC-6. They function in joining or forming new bonds.
EC 4.2.1.7 belongs to the group of lyases. This enzyme named as D-altronate dehydratase catalyses the dehydration of D- altronate and brings about formation of 2-dehydro-3-deoxy-D-gluconate and water.

Thus, the correct answer is option B.

Note:
EC number stands for Enzyme Commission number. It was started in 1955. Some examples of lyases are decarboxylase. The peptidase, amylase belongs to the category of hydrolases as they bring about hydrolysis.