Pseudoenzymatic dealkylation of alkyltins by biological dithiols

We investigated the time dependence of the degradation of three alkyltin derivatives by a nine amino acid linear peptide (I(1)LGCWCYLR(9)) containing a CXC motif derived from the primary sequence of stannin, a membrane protein involved in alkyltin toxicity. We monitored the reaction kinetics using the intrinsic fluorescence of the tryptophan residue in position 5 of the peptide and found that all of the alkyltins analyzed are progressively degraded to dialkyl derivatives, following a pseudoenzymatic reaction mechanism. The end point of the reactions is the formation of a covalent complex between the disubstituted alkyltin and the peptide cysteines. These data agree with the speciation profiles proposed for polysubstituted alkyltins in the environment and reveal a possible biotic degradation pathway for these toxic compounds.