Deuterium isotope effects on the central carbon metabolism of Escherichia coli cells grown on a D2O-containing minimal medium

In this paper it is demonstrated that cross-correlated time modulation of isotropic chemical shifts (`conformational exchange') leads to differential relaxation of double- and zero-quantum coherences, respectively. Quantitative information can be obtained from the time dependence of the interconversion between the two two-spin coherences 2I_xS_x and 2I_yS_y, induced by the differential relaxation. The effect is illustrated with an application to ¹³C,¹⁵N-labeled quail CRP2(LIM2), by studying ¹⁵N-¹H^N multiple-quantum relaxation. Significant cross-correlated fluctuations of isotropic chemical shifts were observed for residues which are part of a disordered loop region connecting two -strands in CRP2(LIM2). Differential ¹H^N and ¹⁵N exchange contributions to multiple-quantum relaxation observed at these sites illustrate the complex interplay between hydrogen bonding events and conformational reorientations in proteins.