Analysis of metallothioneins by means of capillary electrophoresis coupled to electrospray mass spectrometry with sheathless interfacing

Capillary electrophoresis (CE) coupled to electrospray mass spectrometry via sheathless interfacing has been applied to the analysis of mammalian metallothionein (MT) extracts. In a rabbit-liver extract, four (MT-2C, MT-2A, MT-2D and MT-2E) out of six known MT sub-isoforms were unambiguously identified under three CE-resolved peaks. A fourth peak was found to contain MT-1A and/or MT-2B, whose molecular masses differ by only 1 Da. Traces of non-N-acetylated MT-2D and MT-2E were observed in a fifth, minor peak. In a rat-liver extract, both MT-1 and MT-2 were resolved and identified. Non-N-acetylated MT-2 was also identified in a resolved, minor peak. Minimum detectable amounts of MTs have been estimated to be approximately 0.6 fmol per sub-isoform.