摘要

The magnitude of the N-15 longitudinal relaxation rate typically decreases as magnetic field strength increases in globular proteins in solution. Thus, it is important to test the performance of N-15 longitudinal relaxation experiments at high field strength. Herein, a tool to investigate systematic errors in N-15 longitudinal relaxation rate, R-1, is introduced. The tool, a difference in R-1 values between the two components of the H-1-coupled N-15 magnetizations, R (1) ((1)) -R (1) ((2)) , conveniently detects inefficiencies in cancellation of cross correlation between H-1-N-15 dipolar coupling and N-15 chemical shift anisotropy. Experiments, in varying conditions, and simulations of a two-spin system indicate that insufficient cancellation of the cross correlation is due to (1) H-1 pulse imperfection and (2) H-1 off-resonance effect, and (3) is further amplified by residual N-15 transverse magnetization that is caused by the N-15 off-resonance effect. Results also show that this problem can be easily and practically remedied by discarding the initial decay points when recording N-15 longitudinal relaxation in proteins.

  • 出版日期2014-2