Relationships between iron and vanadium metabolism: the exchange of vanadium between transferrin and ferritin

The study of possible relationships between iron and vanadium metabolism (E. Sabbioni and E. Marafante, Proc. XIth Int. Conf. Biochem., 13-5-R122, Toronto, Canada) was extended to the vanadium in the biochemical mechanisms which involve the exchange of iron between transferrin and ferritin. The transfer of vanadium between transferrin and ferritin was investigated using 48V radiotracer and gel filtration technique. 48V labeled human transferrin and horse spleen ferritin, 48V plasma from rats injected with 48VO2+, unlabelled rat liver cytosol, and plasma were used as sources of the two proteins for their incubation under different conditions. The results show that the equilibrium: V - transferrin in equilibrium V - ferritin occurs in vitro at physiological pH under the conditions of this experiment. No transfer of vanadium between the two proteins, however, occurs when they are incubated simply in a buffer at pH = 7.4. The maximum transfer was observed when transferrin and ferritin were mixed in their natural environments such as plasma and liver cytosol. This suggests that the exchange of the vanadium between the two proteins is affected by biochemical factors which are present in the body. A brief evaluation of the significance on the very low amounts of the element exchanged between the two proteins is also presented.