Enzyme mechanism: The post-binding conformational change that allows catalysis to proceed is best explained by which model?

Introduction:
After a substrate initially binds, many enzymes undergo a shape change that better positions catalytic groups. The conceptual model that captures this substrate-triggered adjustment is called the induced fit model.

Given Data / Assumptions:

• Substrate binding precedes catalysis.
• Conformational changes can alter active-site geometry and catalytic residue orientation.
• General enzyme kinetics context (Michaelis–Menten compatible).

Concept / Approach:
The induced fit model proposes that binding energy is used to drive conformational rearrangements, optimizing complementarity to the transition state and aligning catalytic residues, cofactors, and ordered water molecules for reaction.

Step-by-Step Solution:
1) Initial encounter complex forms with modest complementarity.2) Substrate binding energy promotes active-site closure or repositioning of loops/domains.3) New geometry stabilizes the transition state and lowers activation energy, accelerating chemistry.4) After product formation, the enzyme returns (fully or partly) to its original conformation, enabling turnover.

Verification / Alternative check:
Structural biology (X-ray, cryo-EM, NMR) shows substrate- or analog-bound states with different conformations versus apo enzymes; rapid kinetics (stopped-flow) detects conformational steps preceding chemistry.

Why Other Options Are Wrong:

• (b) Lock-and-key: assumes rigid complementarity; does not account for post-binding adjustment.
• (c) Transition state stabilization is real but typically accompanies induced fit; ignoring conformational change is incomplete.
• (d) Allosteric activation can occur but is not the generic explanation for the substrate-triggered change at the active site.
• (e) Vitalism is a historical notion, not a mechanistic model.

Common Pitfalls:
Equating lock-and-key with all enzyme behavior; forgetting that dynamic flexibility is central to catalysis.

Final Answer:
Induced fit model