Nuclear Magnetic Resonance Studies of Proteins

Abstract

SUMMARY The proton magnetic resonance spectra of a number pro- teins have been observed in DzO under various conditions. The proteins examined included ribonuclease, bovine serum albumin, fi-lactoglobulin, pepsin, pepsinogen, chymotrypsin, chymotryp- sinogen, ovalbumin, aldolase, insulin, cytochrome c, myoglobin, lysozyme, and yeast alcohol dehydrogenase. The spectra range from low, broad, unresolved bands to sharply defined peaks with structure. The latter type of spec- trum reflects the amino acid composition of the protein. In the sequence, native ribonuclease, urea denatured protein, and performic acid oxidized protein, the spectra undergo a progressive narrowing and increase in resolution. Similar changes are ob- served between native and urea denatured forms of bovine serum albumin, aldolase, and chymotrypsin. A sharp, well re- solved spectrum is exhibited by the A chain of insulin, but not by the B chain. Insulin itself shows a moderately resolved spectrum. The increase in resolution is attributed to an increase in the segmental motions of the peptide chain which decrease the effectiveness of dipole-dipole interactions. Absorptions of protons bonded to nitrogen which exchange very slowly with the solvent can be observed in the spectra of ribonuclease, insulin, and other proteins. The spectra of cytochrome c and myoglobin exhibit anomalous absorptions at very high fields and in the region of 47. These arise possibly through a ring-current effect of the porphyrin. The spectra of these two proteins change with the oxidation state of the iron. The differences that are observed probably arise from a modification in the structure of the protein moiety rather than from a change in the electronic spin relaxation time of the iron. Acknowledgments-This investigation was supported by United States Public Health Research Grant A-2316. The author is deeply indebted to Dr. Paul Boyer, in whose laboratory this work was carried out, for support, advice, and encouragement, and to Drs. Rufus Lumry and Edward Westhead for many helpful discussions. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. REFERENCES