Figure 3

Electrospray ionization (ESI) time-of-flight mass spectroscopy (MS) spectra of the different metal-metallothionein (MT) complexes obtained when recombinantly synthesizing the MT peptides with their 'non-cognate' metal ion. (a) HpCdMT produced in Cu-enriched medium and; HpCuMT in (b) Cd- and (c) Zn-enriched media, where M stands for Zn+Cu, due to the difficulty of ESI-MS to discriminate between these two metal ions. For the Zn and Cd-enriched preparations, the MS spectra show the +4 charge state (intensity vs m/z) obtained for each preparation, while in the protein produced in a Cu-enriched medium, the MS spectrum shows the +5 charge state (intensity vs m/z). inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis of these preparations indicated a mean content of 0.8 Zn/MT and 7.7 Cu/MT for HpCdMT in (A); 7.8 Cd/MT in (B) and 4.8 Zn/MT in (C) for HpCuMT.