FOUR FIGURES
I n previous papers of this series (Rothstein and Larrabee, '48 ; Rothstein, Frenkel and Larrabee, '48 ; Rothstein, Rleier and Hurwitz, '51; Rothstein and Meier, '51), it has been shown that the uranyl ion specifically inhibits the metabolism of hexoses by forming a highly undissociated but reversible compEex with specific loci on the surface of the cell. These loci possess certain chemical characteristics typical of polyphosphates, suggesting that uranium interferes with sugar metabolism by preventing phosphorylation reactions on the surface of the cell. This hypothesis is predicated on the concept that sugars are actively transported into the cell by a mechanism involving enzyme reactions on the cell surface, with consequent chemical alteration of the sugar molecule as it passes through the cell-membrane.
Assuming that the above hypothesis is essentially correct, then the uranium-inhibited reactions are enzymatic reactions and should display the general properties of enzymatic reactions. An alternative hypothesis is based on the classical concept of permeability, in which the cell-membrane This paper is based on work performed under contract with the TJnited S t a t e Atomic Energy Commission at the TJniversity of Rochester Atomic Energy Project,