Practice question

In apolar protein core, tryptophan is shielded from water and polar side chains, minimal solvent relaxation occurs, excited state dipole remains poorly stabilized, gap stays large, photon retains higher energy. Emission appears blue-shifted near 325 to 335 nanometers, sometimes as low as 308 nanometers in highly rigid environments like azurin. Surface exposed tryptophan emits near 350 nanometers. This blue-shifted maximum is hallmark of burial, useful to monitor folding, membrane protein insertion or ligand-induced conformational sequestration from solvent without adding external labels.