Radiation-induced binding yields of sulfur-containing amino acids, aromatic amino acids and nucleic acid bases with macromolecular substances in the cell lysates of <tex-math>$Escherichia\ coli$</tex-math>, in mammalian cell (L5178Y) lysates, and in intact cells of L5178Y were measured as a function of gamma-ray dose. The binding yields of cysteine and cystine exceeded the yields of the others, both for cell lysates and for whole cells. The binding of these amino acids and bases with nucleic acid was observed only with intact cells. Binding ratios for cysteine with protein, nucleic acid and lipid in intact cell were 35, 20, and 45%, respectively, of the total binding. Sedimentation analysis showed that cysteine was bound mainly to protein and probably to lipid, and that RNA was cross-linked with other high molecular substances (mainly protein) by irradiation.

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