Characterization and Quantitation of Metallothionein Isoforms Induced in a Cyanobacterium Using Reversed-Phase HPLC/ICP Mass Spectrometry

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By combining reversed-phase high-performance liquid chromatography (RP-HPLC) with inductively coupled plasma mass spectrometry (ICPMS), the induction of two major metallothionein (MT) isoforms has been demonstrated for a cyanobacterium Anacystis nidulans R-2, cultured under a stress of Zn²⁺ or Cd²⁺. The two isoforms showed only a slight difference in the amino acid composition. Incubation of two Zn-MT isoforms in a medium containing Cd²⁺ led to a metal exchange, reflecting the higher affinity of MT to Cd²⁺ than to Zn²⁺. During this process the relative abundance of the two isoforms remained practically unchanged. The two isoforms were induced in a constant ratio by the Zn²⁺ dosage (1-20μM), while by the Cd²⁺ dosage (0.5-10μM) the ratio showed a change with the dose level. These results demonstrate the potential of the present RP-HPLC/ICPMS system to elucidate the function of MT isoforms.