In MerT, the mercury transporter, a first cysteine pair, located in the first trans-membrane helix, receives mercury from the periplasm. Then, a second cysteine pair, housed in a cytoplasmic loop connecting the second and the third trans-membrane helices, is thought to transfer the metal to another cysteine pair located in the N-terminal extension of the mercuric reductase. We found that a 23-amino acid synthetic peptide corresponding to the cytoplasmic loop can bind one mercury atom per molecule and that this mercury atom can be transferred specifically to MerAa. The solution structure of Hg-bound ppMerT has been solved by 1H NMR spectroscopy.