Rat metallothionein-2 contains N-alpha-acetylated and unacetylated isoforms

John Hamilton Beattie, Alison Wood, Gary James Duncan

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    Abstract

    Mammalian metallothioneins (MT), are characteristically N-alpha-acetylated and the presence of an unblocked N-terminus has not previously been reported. On-line capillary electrophoresis-electrospray mass spectrometry of hepatic MT-2 from rats injected with zinc revealed two isoforms differing by a mass equivalent to that of a single acetyl group. The lower mass component constituted > 20% of total MT-2 protein and both MT-2 isoforms were separated by reversed-phase high-performance liquid chromatography. The identity of each fraction was confirmed by matrix-assisted laser desorption ionisation mass spectrometry, and amino acid analysis and N-terminal sequencing revealed that the lower mass isoform was unblocked at the N-terminus and had an amino acid composition and sequence which is characteristic of rat MT-2. Thus the complementary techniques of mass spectrometry and K-terminal sequencing demonstrated conclusively that purified MT-2 from zinc-treated rats contains an unacetylated isoform. We propose that the cotranslational acetylation of rat MT-2 may under some circumstances be inefficient compared to that in other nonrodent species, where we have detected only trace levels of unacetylated MT isoforms.

    Original languageEnglish
    Pages (from-to)1613-1618
    Number of pages6
    JournalElectrophoresis
    Volume20
    Issue number7
    Publication statusPublished - Jun 1999

    Keywords

    • Metallothionein
    • isoforms
    • acetylation
    • translation
    • capillary electrophoresis
    • mass spectrometry
    • electrokinetic capillary chromatography
    • liver
    • separation
    • cells
    • isometallothioneins
    • electrophoresis
    • induction

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