The influence of a scalar-coupled deuterium upon the relaxaton of a 15N Nucleus and its possible exploitation as a probe for side-chain interactions in proteins.

The magnitude of the quadrupole coupling constant (e2Qq/h) of a deuteron is a good probe for hydrogen bonding. In protein structures, hydrogen-bonding interactions between side chains, between side chaings and ligands, and between side chains and solvent are frequently found. An experiment that detects, via scalar coupling, the influence of a deuteron on the 15N nucleus of asparagine or glutamine side chains is presented. The experiment depends upon the resolution of the 1 delta 15 N(D) isotope shifts that allow the various isotopomers and isotopologues to be distinguished when 15N-labeled samples are dissolved in solvent mixtures of H2O/D2O. 15N lineshapes with theoretical simulations that provide estimates for the 2H quadrupole coupling constants are presented. The influence of 15N-2H dipolar-quadrupole cross correlation and the resulting small frequency shifts in the 15N multiplet are resolved in some of the spectra. The experimental data are provided using the free amino acids asparagine and glutamine for which the side chains were isotopically enriched in 15N and the recombinant pair of modules, fibronectin type 1 and epidermal growth factor, (F1-G) of tissue plasminogen activator, which were uniformly isotopically enriched in 15N.