= Solution
\b[Yes: the binding data support strong positive cooperativity.] On the linear <concentration> axis, occupancy rises sigmoidally, with reported <Hill coefficient> $n=3.97\pm0.13$, far above the noncooperative value one. The <Hill equation> gives the useful empirical description
$$
\theta=\frac{[L]^n}{K_{1/2}^{\,n}+[L]^n},\qquad K_{1/2}\simeq0.90\,\mu\mathrm M.
$$
The steep response is consistent with the independent evidence for a four-subunit assembly. The fitted half-occupancy <concentration> is not automatically the microscopic <dissociation constant> of one isolated site.
Binding alone does not demonstrate which conformational change is coupled to occupancy. Here the microscopy supplies the complementary structural evidence, so together the observations support a cooperative ligand-dependent switch. A <Hill coefficient> near four is consistent with strongly coupled binding in a tetramer, but is not an independent exact count of <ligands>.
\Image[/past-exam-of-the-biochemistry-course-of-the-university-of-cambridge/2025/paper-5-cooperative-binding.png]
{title=Illustrative binding curves showing how a Hill coefficient near four sharpens the response}
Back to article page
