Question

The following reaction depicts the activity of a particular class of enzymes :

X    Y
|    |
C - C → X - Y + C = C

(Substrate)      (Product)    (Product)

Identify the enzyme class 'E' from the following options :

• A. Ligases
• B. Transferases
• C. Lyases
• D. Isomerases

Hint:

Logic Tip: The key visual cue for a Lyase reaction is the formation of a double bond upon the removal of groups. No water involved (not a hydrolase) + double bond created = Lyase.

Answer 1

The Correct Option is C

Concept:
Enzymes are classified into six major classes by the IUBMB based on the specific type of chemical reaction they catalyze. Recognizing the functional mechanism from a general chemical equation allows you to identify the enzyme class.
Step 1:
The substrate is a molecule with a single carbon-carbon bond ($C-C$), where groups $X$ and $Y$ are attached to adjacent carbon atoms. The reaction cleaves these groups off the substrate without the addition of water (it is not a hydrolysis reaction).
Step 2:
The cleavage results in two products: the separate $X-Y$ molecule, and a modified carbon structure where the removal of the groups leaves behind a double bond ($C=C$).
Step 3:

• Ligases catalyze the joining together of two molecules (e.g., forming C-O, C-S, C-N bonds). This reaction is a breakdown, not a joining.
• Transferases catalyze the transfer of a functional group from one substrate to another. Here, groups are removed entirely to form a double bond, not transferred to another molecule.
• Isomerases catalyze the structural rearrangement within a single molecule (optical, positional, or geometric isomers). This reaction breaks a molecule into two pieces, so it's not isomerization.
• Lyases catalyze the removal of groups from substrates by mechanisms other than hydrolysis, specifically leaving double bonds. This perfectly describes the given reaction mechanism.
Step 4:
The reaction strictly defines the mechanism of action for a Lyase enzyme. Therefore, Option (3) is correct.