PROBING PROTEIN-STRUCTURE BY SOLVENT PERTURBATION OF NMR-SPECTRA - A COMPARISON WITH PHOTOCHEMICALLY INDUCED DYNAMIC NUCLEAR-POLARIZATION TECHNIQUES APPLIED TO NATIVE ALPHA-LACTALBUMIN

We have suggested elsewhere the use of surface mapping by spin label p robes (Esposito et al., 1992). According to this approach, soluble nit roxides are added to a protein solution. Resonances of protons that ar e accessible to the nitroxide are broadened and bleached out of the sp ectrum, while resonances in the protein interior remain unaffected. Th is approach is, in principle, complementary to another technique, phot ochemically induced dynamic nuclear polarization, which maps the posit ion of aromatic protons on the protein surface. A detailed comparison between the two techniques is necessary for a confident use of the mor e recent suggested nitroxide perturbation approach. In the present stu dy, we show that the results obtained by the two techniques for the na tive state of bovine alpha-lactalbumin are fully consistent and may th erefore be combined for the study of protein surfaces.