199Hg NMR spectroscopy is used to examine the interaction of the toxic organomercurial ethylmercury phosphate [2235-25-8] with various amino acids. Because of the relative insensitivity of 199Hg and the low concns. of biol. mols., a heteronuclear spin-echo and a 2-dimensional technique involving a double transfer of polarization are used to bypass the concn. limits of direct detection. The chem. shifts of 199Hg cover a wide range (600 ppm for ethylmercury derivs.) and are diagnostic for the identity of the ethylmercury adduct. Based on the Hg chem. shifts and pH stability detd. for adducts of the ethylmercuric ion [21687-36-5] with individual amino acids, the ethylmercury-RNase [9001-99-4] adduct may involve modification of the N-terminal lysine [56-87-1] residue. [on SciFinder (R)]