Patent ID: 6979531

Claim:
A method for identifying an exposed position of a macromolecule, comprising the steps of (a) obtaining a sample comprising a macromolecule and a second molecule, wherein the macromolecule is larger than 35 kiloDaltons and has a position that is exposed to the second molecule, wherein a first proton is bound to the exposed position of the macromolecule, a second proton is bound to the second molecule, and the first proton exchanges with the second proton; (b) applying a magnetic field to the sample, thereby magnetizing the first proton and the second proton; (c) irradiating the sample with a sea-trosy pulse sequence that preferentially demagnetizes the protons of the macromolecule relative to the second proton; (d) allowing the second proton to exchange with the first proton, whereby the relatively magnetized second proton becomes bound to the exposed position of the macromolecule; and (e) detecting the magnetization from the second proton; whereby the exposed position of the macromolecule is identified.