Fluorometric study of the isoform difference of mammalian metallothionein

A fluorometric method for studying the isoform difference of mammalian metallothionein (MT), which lacks aromatic amino-acid residues, is reported. Cadmium-induced rabbit and hedgehog liver MT exhibited a strong luminescence signal in the range of 335 to 340 nm when excited at 285 nm in aqueous solution. The differences in emission intensity of the two major isoforms of MTs are significant. When titrated with chloride acid, which is believed to proton the metal-thiolate coordination bound to the -SH group in MT, a 10-nm red-shift property of the emission spectrum was observed, and the red-shift properties of the isoforms varied with the species. The observed fluorescence property of MT was considered to be the result of its polypeptide chains, which was confirmed by comparing the luminescence and absorption spectra during the titration of MT with diethylenetriaminepentaacetic acid. The new luminescence property of MT should be useful in studying the isoform and function difference of MT.