Allosteric enzymes compared to simple (Michaelis–Menten) enzymes: which description best characterizes their size and complexity?

Introduction / Context:
Allosteric enzymes regulate metabolic flux by responding to effectors at sites distinct from the active site. Their structural properties underpin cooperative behavior and sigmoidal kinetics observed in pathways such as glycolysis.

Given Data / Assumptions:

• Allosteric enzymes typically consist of multiple subunits (quaternary structure).
• They possess regulatory (allosteric) sites in addition to catalytic sites.
• Simple enzymes often follow classic Michaelis–Menten kinetics and can be monomeric.

Concept / Approach:
To accommodate multiple binding interactions (substrate plus allosteric effectors) and cooperative transitions (T ↔ R states), allosteric enzymes are usually larger oligomeric proteins with several polypeptide chains. This added quaternary complexity enables regulation of activity in response to cellular signals.

Step-by-Step Solution:

Verification / Alternative check:
Examples include aspartate transcarbamoylase and phosphofructokinase-1, which are multimeric and regulated by allosteric effectors, exhibiting sigmoidal velocity–substrate curves.

Why Other Options Are Wrong:
Smaller/less complex: Contradicts the need for multiple subunits and regulatory domains. “Larger than” alone: Incomplete; complexity is also crucial.

Common Pitfalls:
Assuming all multi-subunit enzymes are allosteric; while many are, the key is the presence of regulatory sites and cooperative behavior.

Final Answer:
larger and more complex than simple enzyme