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 re ported. Cadmium-induced rabbit and hedgehog liver MT exhibited a stron g luminescence signal in the range of 335 to 340 nm when excited at 28 5 nm in aqueous solution. The differences in emission intensity of the two major isoforms of MTs are significant. When titrated with chlorid e acid, which is believed to proton the metal-thiolate coordination bo und to the -SH group in MT, a IO-nm red-shift properly of the emission spectrum was observed, and the red-shift properties of the isoforms v aried with the species. The observed fluorescence property of MT was c onsidered to be the result of its polypeptide chains, which was confir med by comparing the luminescence and absorption spectra during the ti tration of MT with diethylenetriaminepentaacetic acid. The new lumines cence property of MT should be useful in studying the isoform and func tion difference of MT.