Mechanism of uptake of cobalamin into enterocyte mitochondria

To study the mechanism which cobalamin is taken up by the mitochondria, 57Co-cyanocobalamin-binder complex and freshly prepared mitochondria were prepared from the enterocytes of rats. Subsequently, the binder complex was incubated together with mitochondria 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 completely restored after addition of calcium ions to the mitochondria.