To study the mechanism which cobalamin is taken up by the mitochondria, ⁵⁷Co-cyanocobalamin-binder complex and freshly pre-pared mitochondria were prepared from the enterocytes of rats. Subsequently, the binder complex was incubated together with mitochon-dria in a calcium-containing medium in vitro. Uptake of cobalamin was determined by measuring the radioactivities bound to the mitochondria. Consequently, lysosomal and microsomal binders enhanced cobalamin uptake into the mitochondria, but intrinsic factor did not.
It was found that the uptake into the mitochondria was inhibited by previous treatment with calcium-chelating agents. The uptake was com-pletely restored after addition of calcium ions to the mitochondria.