Romney wether sheep were given ZnO on a regular basis, as required in protocols for the treatment of facial eczema, at either 12 g ZnO fortnight(-1) or 12 g ZnO week(-1), and the effect of Zn on the synthesis of different metallothionein (MT) isoforms isolated from liver tissue characterized and quantified. Metallothionein isoforms in liver of dosed and non-dosed sheep were quantitatively determined by reverse phase HPLC, with markedly increased concentrations of total MT-Ia protein found in the liver tissue of Zn-dosed groups (634 mu g g(-1) fresh weight for the weekly dosed group) compared with 49 mu g g(-1) fresh weight in non-dosed sheep. The concentration of MT-II protein was not significantly increased. Individual sheep varied widely in the relative amounts of each MT isoform expressed with increased amounts of types of MT-Ia especially and MT-II in some animals, which bound predominantly Cu. The half-lives for [S-35]-cysteine and Zn-67 in MT isoforms from weekly dosed sheep were found to be 2.5-3.5 days and 5-24 h respectively, indicating relatively fast exchange of Zn with MT compared with synthesis. Rate of synthesis for MT-Ia was twice that for MT-II. Data reflecting relationships between MT isoforms, Cu and Zn concentrations in liver are presented and discussed.
