Detection of Metallothionein Isoforms from Three Different Species Using On-Line Capillary Electrophoresis–Mass Spectrometry

An on-line capillary electrophoresis–mass spectrometry method (CE–MS) for the detection of metallothionein (MT) isoforms is described. The detected masses were usually within 1–1.5 mass units of the expected molecular weights. MT-containing samples from rabbit, sheep, and yeast (Saccharomyces cerevisiae) were subjected to CE–MS analysis. The analysis of rabbit liver MT revealed the masses of 10 proteins/peptides. Five of the detected masses corresponded well with the expected masses calculated from the amino acid sequence of previously described MT isoforms, one was suspected to be a deacetylated form of MT-2A, one was presumed to be a yet unknown isoform, and three masses were classified as non-MT compounds. From the analysis of a fetal sheep liver extract six proteins were detected of which three masses corresponded to previously described MT isoforms. Two purified MT subforms fromS. cerivisiae(encoded by theCUP1locus) were analyzed for their copper content and both forms were found to contain eight copper atoms per molecule.