Cupric Ion Stimulation of Mitochondrial Protein Synthesis and Dependence on the Osmolarity of Incubation Medium

Abstract

The effect of cupric ion on amino acid incorporation into protein by isolatec rat liver mitochondria was investigated. In confirmation of previous observations, the incorporation was stimulated as much as 80% by the addition of 2 to 10 μM CuCl₂ when the mitochondria were incubated in the medium of Buchanan et al. The stimulation was maximal at 6 μM Cu²⁺. By contrast, cupric ion at comparable concentrations showed no significant effect on the incorporation when the mitochondria were incubated in the medium of Haldar and Freeman. Experiments involving omission or addition of the components which made the two media different showed that the stimulatory effect of cupric ion depended upon the presence of 50 mM Tris-HCl. Additional experiments with Tris-HCl and sucrose demonstrated that the extent of stimulation depended on the osmolarity of the incubation medium and that cupric ion stimulated the incorporation by preventing the inhibition caused by the hyperosmolarity of the medium.