Biological significance of non-acetylated metallothionein

Abstract

The biological significance of non-acetylated metallothionein (MT) was investigated from the viewpoint of N α -acetylation after induction of MT synthesis by metallic and non-metallic inducers, by partial hepatectomy and under physiological conditions. N α -Acetylated and non-acetylated forms of MT-2 in liver supernatants and plasma were detected by the tandem size-exclusion and anion-exchange HPLC columns with in-line detection by mass spectrometry. The non-acetylated isoform of MT-2 (MT-2′) was present at a comparable level to the N α -acetylated form of MT-2 (MT-2) at an early stage after induction by not only zinc but also cadmium, and by partial hepatectomy in the livers of rats. Plasma MT-2 in neonatal rats was similar to liver MT-2 in the composition of N α -acetylated and non-acetylated forms, suggesting that there are no differences in the roles of N α -acetylation of MT in the extracellular trafficking of MT. The column switching HPLC method with in-line detection by inductively coupled argon plasma mass spectrometry (ICP-MS) was shown to be a sensitive and powerful method to detect MT proteins at not only isoform level but also at acetylated and non-acetylated form levels.