The 109Cd binding assay of Eaton & Toal was critically evaluated and then used to assess the induction of cytosolic metal-binding ligands in rainbow trout exposed to Zn in the diet and/or in the water for 16 weeks. With purified rabbit Cd-Zn metallothionein (MT), 109Cd binding and total Cd recovery in the assay were linear up to 5 μg of protein; gel chromatography revealed a single peak. With heat-denatured extracts of gill, liver and intestine from control and Cd- and Zn-injected trout, 109Cd binding was generally linear with sample size. Gel chromatography demonstrated that 109Cd was bound by a protein with the same apparent weight as MT (∼11 000 daltons), but significant binding occurred also at three other regions [molecular weight (mol wt) > 70 000, 30 000 and <3000]. In the dietary/waterborne Zn exposure, induced 109Cd-binding activity occurred not in the MT peak but in the low mot wt peak (<3000). Activity in the gill rose in response to both dietary and waterborne Zn, but the liver did not respond. The maximum fivefold elevation in the gill was primarily a waterborne effect. In the intestine, the maximum rise was 25-fold due to both factors. The thresholds for induction were > 39 μg Zn l-1 in water, and > 90 mg kg-1 in the diet, but only when waterborne Zn was also high. There was no correlation between 109Cd binding and acid soluble thiol levels, which tended to decline at higher Zn exposures.
|Number of pages||20|
|Journal||Journal of Fish Biology|
|State||Published - Oct 1 1989|
- metal ligands
- rainbow trout
ASJC Scopus subject areas
- Aquatic Science