PROTON NUCLEAR MAGNETIC-RESONANCE STUDIES OF BENCE-JONES PROTEINS

His-198 resonances probably reflects the Meg isotypic substitutions. The constant fragment (CL) obtained by limited tryptic digestion of the X-type Bence-Jones protein Nag was also examined and the results were compared with those for the intact X-type Bence-Jones proteins. It was concluded that the tertiary structure of the immunoglobulin fold is well preserved even in the CL fragment. 1H NMR spectra of three kinds of k-type Bence-Jones proteins were examined. There is a difference between X- and k-type Bence-Jones proteins in the His-189 and more significantly in the His-198, titration curves. We suggest that the difference in the chemical shift of the His-189 resonances makes it possible to quantitate the λ/k ratio for the normal light chain. It was shown that His-198 in the k-type Bence-Jones proteins is much more difficult to protonate; the His-198 peak begins to shift downfield only below pH 4, where the proteins begin to denature. We conclude that λ- and k-type Bence-Jones proteins are basically similar in conformation in the constant domain. However, the constant domain of the k-type proteins appears to be more compact than that of X-type proteins. © 1979, American Chemical Society. All rights reserved.