Quantitative measurement of small through-hydrogen-bond and ‘through-space’1H-113Cd and1H-199Hg J couplings in metal-substituted rubredoxin fromPyrococcus furiosus
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- Blake, P.R., Lee, B., Summers, M.F. et al. J Biomol NMR (1992) 2: 527. doi:10.1007/BF02192814
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A method is described for measurement of small unresolvable heteronuclear J couplings. The method is based on quantitative analysis of a phase-purged heteronuclear spin-echo difference spectrum, and is demonstrated for measuring1H-113Cd and1H-199Hg J couplings in metal-substituted rubredoxin (Mr ∼ 5.4 kDa) fromPyrococcus furiosus. Couplings from cadmium to backbone amide protons that are hydrogen bonded to the Cys-S atoms directly bonded to Cd vary from smaller than 0.3 to 1.8 Hz; a ‘through-space’ coupling between Cd and the protons of an alanine methyl group was measured to be 0.3 Hz. Couplings to199Hg are significantly larger and fall in the 0.4–4 Hz range.