Binding behavior for two independent sites: curve shapes and plots A protein binds two ligands in a noncooperative fashion. Which binding-curve and Scatchard characteristics best describe this system?

Introduction / Context:
Noncooperative binding arises when multiple sites bind independently with identical affinities. Recognizing the expected data signatures helps in diagnosing mechanisms from experimental curves.

Given Data / Assumptions:

• Two identical, independent binding sites.
• No allosteric interaction between sites.
• Classical equilibrium binding readouts.

Concept / Approach:
Independent binding leads to a sum of hyperbolic terms that reduces to a single hyperbola for identical sites when expressed as fractional saturation. Scatchard plots of such systems are linear with slope related to the affinity and intercept related to the number of sites.

Step-by-Step Solution:
Identify curve shape: noncooperative systems yield hyperbolic saturation versus ligand concentration.Scatchard analysis: r/[L] versus r is linear for identical independent sites.Therefore, both hyperbolic behavior and linear Scatchard are expected.

Verification / Alternative check:
Fitting data to the Langmuir isotherm confirms a single apparent Kd and linear Scatchard behavior.

Why Other Options Are Wrong:
Sigmoidal curves indicate cooperativity; claiming none of the above contradicts standard binding theory.

Common Pitfalls:
Pooling heterogeneous sites with different Kd values produces curvature in Scatchard plots and can be misread as cooperativity.

Final Answer:
Both (b) and (c).