113Cd‐1H spin‐spin couplings in homonuclear 1H correlated spectroscopy of metallothionein

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Abstract
Heteronuclear spin‐spin couplings between 113Cd and Cβ protons of the metal‐bound cysteines were observed in phase‐sensitive, double‐quantum filtered, homonuclear two‐dimensional correlated (COSY) 1H NMR spectra of 113Cd‐metallolhionein‐2 from rabbit liver. Comparison of 113Cd‐and 112Cd‐metallotriionein‐2 spectra revealed that 19 1H spin systems show heteronuclear couplings to at least one 113Cd and were thus identified as 19 of the 20 cysteines in this protein. From a detailed analysis of the manifestations of heteroouelear couplings in the homonuclear 1H COSY speclra, two cyslcincs could be identified as ‘bridging cysleines’, with spin‐spin couplings to two different 113Cd nuclei. The observed 113Cd‐1H coupling constants vary between ≤5 Hz and 80 Hz.