In case of accidental release of radionuclides into the environment, actinides represent a severe health risk to human beings after being incorporated by e.g. inhalation, ingestion or wounds. Contrary to other metal ions, actinides have no known essential function in biochemical reactions occurring in living organisms. The bioavailability and toxic effects depend strongly on the concentration and the speciation (chemical form, oxidation state) of the incorporated actinides. For a better understanding of the actinide behavior and their toxic effects in man (in term of metabolism, retention, and excretion), a fundamental knowledge on the mechanisms of relevant biochemical reactions in the body is needed which can be an important prerequisite for the design and success of potential decontamination therapies.
The interaction of actinides with blood serum proteins can play a major role in the biokinetic behavior of actinides after internal contamination. Transferrin is one of the most important blood serum proteins responsible for the iron transport in blood. The tertiary structure of transferrin consists of distinct C- and N-terminal lobes capable of binding Fe(III). In regular blood serum only approximately 30% of the transferrin molecules are saturated with iron. Consequently, non-saturated transferrin is available for the complexation of other metal ions. Besides iron, about 30 other tri- and tetravalent metal ions have been identified to bind to transferrin, e.g. Ga(III), Al(III), In(III), lanthanid(III) ions. Therefore, transferrin can significantly affect the biodistribution of metal ions in the living organism. Regarding the interaction of transferrin with actinides, a few studies have been performed with uranium, plutonium, and neptunium, whereas little information exists for the trivalent actinides, Am(III) and Cm(III).
We study the interaction of human serum proteins with trivalent actinides and lanthanides using advanced spectroscopic methods such as time-resolved fluorescence spectroscopy (TRLFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. These investigations aim at obtaining detailed information on the speciation and coordination environment of An(III)/Ln(III) protein complexes.