Differential sensitivity of metallothionein-1 and -2 in liver of zinc-injected rat toward proteolysis

The characterization of degradation products of metallothionein (MT) in rat liver is reported. Using gel filtration chromatography on Sephadex G-75 an unknown zinc (Zn)-containing peak was found in livers of rats injected with zinc. It contained at least 13 peptide fractions, designated as LPI-1, LPI-2, LPI-3, LPI-4, LPII-1, LPII-2, LPII-3, LPIII-1, LPIII-2, LPIII-3, LPIII-4, LPIII-5 and LPIII-6. While two of these fractions (LPII-1 and LPIII-4) were identified as the carboxyl-terminal half (alpha-domain) of rat MT-1, LPI-2 and LPI-3 corresponded to the amino-terminal half (beta-domain) of rat MT-2. In contrast, neither the beta-domain of rat MT-1 nor the alpha-domain of rat MT-2 could be recovered. The data may indicate that the two metal clusters of Zn-MT-1 and Zn-MT-2 differ in their stabilities resulting in differences in their susceptibility towards proteolytic degradation.