Water magnetization transfer experiments

A second variation of saturation transfer experiment has been devised by Dalvit and coworkers that uses the transfer of magnetization from the water (167). Water is intimately associated with proteins being bound either within or on the surface of the macromolecu-lar structure. Saturation of the water resonance will lead to protein saturation through a variety of mechanisms, including saturation of the aH resonances, saturation of exchanging protein resonances, and NOE interactions between water and the protein. If a compound is bound to the protein it will also become saturated, and this effect can be used as an indication of ligand binding (167). 

Magnetization transfer (MT) or cross-relaxation spectroscopy, also termed Z-spectroscopy by Grad and Bryant (1990), has been extensively used to obtain information on the spectral Uneshape of protons in macromolecules as well as on relaxation in heterogeneous systems (Calucd and Forte 2009). A MT spectrum was obtained by performing saturation transfer (ST) experiments at many discrete frequencies and plotting the ratio of the steady-state water signal with and without RF saturation as a function of the saturation frequency offset. For spatially homogeneous samples,... 

Fast exchange reactions can be monitored by the SEA-TROSY (Solvent Exposed Amides with TROSY) experiment. Initial filtration of all amide signals and subsequent transfer of magnetization from water allows observation of solvent-exposed amides that are in fast exchange with bulk water (92). 

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