Mechanism of uranium binding to cellular components of microorganisms. II

Knowledge is summed up of the mechanism of inhibition of carbohydrate metabolism by uranyl ions in yeast and bacteria. The inhibition was found of anaerobic fermentation of glucose by undisturbed yeast cells and by cell-free extract to take place at different uranyl concentrations. The course of time dependence of uranium intake by live yeast cells showed that this process is not controlled by diffusion. It is based on complex binding of uranyl to the cell surface. A more detailed study of the process has shown that even with full saturation of the cell surface with uranyl ions the anaerobic metabolism is only inhibited to 90%, the remaining 10% of the metabolism is apparently provided by a different mechanism. Other centres were discovered on the surface of the yeast cell which do not take part in the anaerobic intake of glucose but form complexes with the uranyl. Mg2+, Ca2+, Ba2+, Mn2+, Cu2+, Ni2+, Co2+, Fe2+ and other bivalent cations can compete with uranyl binding to active cell centres. The most stable complex, however, is formed by the uranyl ion. A more detailed clarification of the chemical character of active centres of the cell surface was made by comparative studies of the stability of the uranyl complex with yeast cells and similar complexes of model compounds. The most stable complex bonds were found to exist in highly polymerated inorganic phosphates. (E.S.)