Protein-mediated polarization transfer: Ligands L1 and L2 that competitively bind to a protein are subject to indirect spin-polarization transfer through the binding site of the protein. If protons H_L1 of one ligand are hyperpolarized by dynamic nuclear polarization (DNP, see picture), signal intensities in the NMR spectrum of the second ligand become enhanced. The relative build-up of signal of the second ligand yields information on its binding epitope.