CHARACTERIZATION OF PROTEIN ADDUCTS PRODUCED BY N-METHYLDITHIOCARBAMATE AND N-METHYLDITHIOCARBAMATE ESTERS

The toxicity of N-methyldithiocarbamate may be mediated through decomp osition to more biologically active compounds. Two principal products, CS2 and methyl isothiocyanate, have the potential to interact covalen tly with macromolecules in biological systems. In this investigation t he ability of N-methyldithiocarbamate to generate methyl isothiocyanat e and CS2 under physiological conditions resulting in acylation and co valent cross-linking of proteins was examined using C-13 NMR and GC/MS . Two N-methyldithiocarbamate esters, S-methyl N-methyldithiocarbamate and (N-acetyl-S-methylthiocarbamoyl)cysteine were also investigated t o evaluate the acylating ability of sulfhydryl conjugates of N-methyld ithiocarbamate. The predominant and most stable adduct produced by the free dithiocarbamate and its S-substituted esters was methylthiourea on epsilon-lysyl and N-terminal alpha-amino groups. Derivatization on N-terminal amino groups progressed more rapidly for the dithiocarbamat e than for its mercapturate. Methylurea protein adducts were also prod uced by the dithiocarbamate and its esters, suggesting production of m ethyl isocyanate in the decomposition of N-methyldithiocarbamate. Cova lent cross-linking of beta-lactoglobulin by N-methyldithiocarbamate re sulting from its decomposition to CS2 was observed using denaturing po lyacrylamide gel electrophoresis. These results demonstrate the abilit y of a monoalkyldithiocarbamate to acylate protein amino groups and ef fect covalent cross-linking. These processes represent molecular mecha nisms that may contribute to the toxicity of this class of compounds.