Recently, NMR methods have been developed to accurately measure one bond 1JNH coupling constants. The apparent 1JNH coupling constant is the sum of the scalar coupling and the residual dipolar coupling. Since the residual dipolar coupling is proportional to the square of the static field and the scalar coupling is constant as a function of field strength, residual dipolar couplings can be measured from the field dependnece of the apparent 1JNH coupling constants. Residual dipolar couplings occur due to the partial ordering of a molecule in the magnetic field and are related to the angle between the N-H bond vector and the magnetic susceptibility tensor. Thus, it has been suggested that residual dipolar couplings could be used as additional constraints in the structure determination of proteins. We propose to measure the residual dipolar couplings for several proteins to determine whether this is a useful constraint in the structure determination of proteins. Although we have access to a 500 and 600 MHz NMR spectrometer for measuring one bond couplings, we need to measure these couplings at higher fields to reliably derive the residual dipolar couplings from the field dependence of the observed 1JNH coupling constants.
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