Question

In Ping pong reaction of enzymes , the first substrate is bound to the enzyme and its product is released before there is binding of the second substrate. Ping pong reactions are also known as :

• A. Random single displacement reactions
• B. Ordered single displacement reactions
• C. Double displacement reactions
• D. Sequential reaction

Hint:

To easily identify Ping-Pong kinetics on a double-reciprocal (Lineweaver-Burk) plot, look for parallel lines at different concentrations of the second substrate.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Multi-substrate enzymatic reactions can proceed via different kinetic mechanisms.
These are broadly classified into sequential mechanisms (where all substrates must bind before any product is released) and non-sequential mechanisms.

Step 2: Detailed Explanation:
The "Ping-Pong" mechanism is a classic example of a non-sequential, double-displacement reaction.
The sequence of events in a double-displacement (Ping-Pong) reaction occurs as follows:
Substrate A binds to the enzyme (E) to form an enzyme-substrate complex (EA).
A functional group is transferred from substrate A to the enzyme, transforming the substrate into product P.
Product P is released from the active site, leaving behind a modified, covalently altered enzyme intermediate (\(\text{E}^*\) or \(\text{F}\)).
Substrate B then binds to this modified enzyme (\(\text{E}^*\)) to form a second complex (\(\text{E}^* \text{B}\)).
The functional group stored on the enzyme is transferred to substrate B, converting it into product Q.
Product Q is released, regenerating the original state of the enzyme (E).
Because this mechanism involves two distinct displacement events—displacement of the first product followed by displacement of the second product—it is known as a double displacement reaction.
Aminotransferases (transaminases) utilize this mechanism to transfer amino groups.

Step 3: Final Answer:
Ping pong reactions are also known as double displacement reactions.