An arsenic-binding protein in rainbow trout.

A pulse dose of 5 microCi 74As-labeled arsenic acid was given in diet contained in No. 4 gelatin capsules to two groups of rainbow trout (90 +/- 6 g). These groups consisted of the control and the treatment group which was preexposed to 22.8 mg As/kg diet for 2 weeks. An extract of cytosol prepared from the liver of both control and pretreated fish sacrificed 48 hr after the pulse dose was found to contain an arsenic-binding protein with molecular weight of about 19,000. This protein accounted for less than 25% of the extracted cytosol in both the control and preexposed fish. Arsenic may not induce the synthesis of thionein in the liver as the molecular weight of 19,000 is outside the range previously reported for metallothionein. The binding of arsenic to this protein may not be of any adaptive significance.