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 language | English |
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Pages (from-to) | 1613-1618 |
Number of pages | 6 |
Journal | Electrophoresis |
Volume | 20 |
Issue number | 7 |
Publication status | Published - Jun 1999 |
Keywords
- Metallothionein
- isoforms
- acetylation
- translation
- capillary electrophoresis
- mass spectrometry
- electrokinetic capillary chromatography
- liver
- separation
- cells
- isometallothioneins
- electrophoresis
- induction