Premium
Rat metallothionein‐2 contains N α ‐acetylated and unacetylated isoforms
Author(s) -
Beattie John H.,
Wood Anne M.,
Duncan Gary J.
Publication year - 1999
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/(sici)1522-2683(19990601)20:7<1613::aid-elps1613>3.0.co;2-t
Subject(s) - gene isoform , mass spectrometry , chromatography , metallothionein , acetylation , chemistry , electrospray , zinc , amino acid , biochemistry , tandem mass spectrometry , protein mass spectrometry , peptide sequence , organic chemistry , gene
Mammalian metallothioneins (MT), are characteristically N α ‐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 N ‐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.