Question

Which is correct for bisubstrate reactions?

• A. They are classified into sequential and double displacement reactions
• B. The most widely used rate expression for them is Michaelis- Menten kinetics
• C. Enzyme concentration is in excess of the substrate in the medium
• D. The rate is mainly limited by the substrate concentration

Hint:

• Bisubstrate reactions involve two substrates.
• Sequential mechanism Both substrates bind before product release (can be ordered or random). Ternary complex (EAB) is formed.
• Ping-Pong (Double Displacement) mechanism First substrate binds, product is released, enzyme is modified. Second substrate binds, second product is released, enzyme regenerated. No ternary complex.
• Michaelis-Menten equation is primarily for single-substrate reactions.

Answer 1

The Correct Option is A

In the context of bisubstrate reactions, which are enzyme-catalyzed reactions involving two substrates, the correct characterization is crucial for understanding their mechanism. These reactions are classified into sequential and double displacement (or ping-pong) reactions:

• Sequential Reactions: In these reactions, all substrates must bind to the enzyme before any product is released. This can further be divided into ordered sequential and random sequential. In ordered sequential, substrates bind and products are released in a specific order. In random sequential, the order can vary.
• Double Displacement or Ping-Pong Reactions: Here, one or more products are released before all substrates bind to the enzyme. An intermediate form of the enzyme is typically involved, where part of the substrate is temporarily attached to the enzyme before the final product forms.

These classifications help to elucidate the kinetic behavior and mechanism of the enzyme-catalyzed process, aiding in biochemical and pharmacological studies. Therefore, the correct option is "They are classified into sequential and double displacement reactions".