Interaction of selenium and arsenic with metallothionein: effect of vitamin B12

The effects of selenium and arsenic on metallothionein (MT) levels were determined in vitamin B12-supplemented and depleted rats. The binding of selenium and arsenic to MT in vitro and in vivo was also investigated. Rats fed a vitamin B12-deficient diet had significant (p < 0.05), higher levels of liver MT as compared to vitamin B12-supplemented rats. Rats fed 5-9 micrograms/g selenium as selenite or 50-150 micrograms/g arsenic as arsenite showed no significant increase of MT content in the liver. However, significant increases in MT levels in liver (p < 0.01) and kidney (p < 0.05) were seen when rats were injected with 1.5 mg selenium as selenite, and increase of liver MT levels (p < 0.05) was shown when injected with 5 mg arsenic as arsenite/kg body weight. In comparison to zinc, injection of selenium or arsenic caused only a slight elevation of liver MT levels. Liver cytosolic Sephadex G-75 patterns of rats injected with both zinc and arsenic gave separate peaks for arsenic and zinc which suggest that in vivo arsenic binding to MT may be insignificant. Spectrophotometric absorption changes at 255 nm with various levels of selenium or arsenic additions to an MT solution were used to show that selenite gave a maximum absorption increase at a 1:1 molar ratio, but maximum absorption change occurred with arsenite at a molar ratio of 7:1.