= Benno Müller-Hill
{c}
\b[<Benno Müller-Hill>], with <Walter Gilbert>, isolated the <lac repressor> in work published in 1966. The research connected a genetically inferred control function with an experimentally detectable molecular component. Their primary paper developed an assay based on binding an inducing small molecule, detected through <equilibrium dialysis> against radioactive <Isopropyl β-D-1-thiogalactopyranoside>.<Isolation of the lac repressor by Walter Gilbert and Benno Müller-Hill>[PNAS 56, printed p. 1891, assay description and Design of the Experiment]{ref}
That choice was logically important. The opening discussion considered a model in which repressor binds the <lac operator>, but the assay sought inducer interaction without requiring every detail of the repression mechanism to be settled first. Measuring binding to an inducer is not itself the same experiment as demonstrating binding to operator DNA.
An original one-site model explains the dialysis signal. A membrane permits free ligand to equilibrate between two compartments while retaining protein on one side. If the common free ligand concentration is $L$, total binding-site concentration is $R_T$ and dissociation constant is $K_d$, the retained bound concentration is
$$
B=R_T\frac{L}{K_d+L}.
$$
The protein-containing compartment has total ligand concentration $L+B$, while the comparison compartment has $L$ under this ideal model. With stipulated $R_T=1\,\mathrm{\mu mol\,L^{-1}}$, $L=K_d=2\,\mathrm{\mu mol\,L^{-1}}$, the totals are 2.5 and 2.0 micromoles per litre. Their excess measures binding even though free ligand equilibrates.
These values are illustrative, not fitted constants from the 1966 experiment. Nonspecific adsorption, unequal accessible volumes and other binding components require controls. <Protein purification> can then be followed with a functional assay rather than by the mere presence of protein material. This is the experimental bridge between a gene-control hypothesis and a molecular mechanism; the joint paper does not justify assigning every experimental operation to Müller-Hill alone.
Back to article page
