HPLC/ICP Mass Spectrometric Study of the Selenium Incorporation into Cyanobacterial Metallothionein Induced under Heavy-Metal Stress

Selenium is a toxic element which can cause environmental pollution. Its uptake and incorporation by Zn2+-induced metallothionein (MT) biosynthesis in a cyanobacterium were studied by means of high-performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometric (ICPMS) detection. When we cultured the cells in selenite-enriched media, as much as 60% of the total selenium in the water-soluble cell components was incorporated into MT, which exists as two major isoforms but occupies a very minor fraction of the overall proteins. Existence of two pathways has been shown for the first time for selenium incorporation into the cyanobacterial MT; one is the S-Se bonding which can be reductively broken by 2-mercaptoethanol, and the other is the formation of selenocysteine followed by its incorporation into the MT peptide chain. No essential difference was noted between selenite and selenate regarding the uptake or the incorporation of Se. The present HPLC/ICPMS system can elucidate biological processes of environmental chemical importance at the molecular level.