 Solution

The unliganded and peptide-bound preparations elute at almost the same volume, near 14 ml. They therefore have similar effective hydrodynamic sizes in this separation. A conformational change can occur without a large change in that measurement. The GFP–peptide-containing complex elutes earlier, near 10.5–11 ml, consistent with a larger particle; the later peak is consistent with excess unbound GFP–peptide.

The experiment supports ligand association but does not alone determine subunit number. Size-exclusion chromatography separates by access to pores, which depends on size and shape rather than mass alone. The similar peptide-free and peptide-bound elution volumes therefore do not establish identical conformations or exact molecular masses.