N-Ethylmaleimide and the Cyclic Response to X-Rays of Synchronous Chinese Hamster Cells

Abstract

In addition to DNA synthesis, at least one other factor appears to exert a controlling influence on the cyclic dependence of the lethal radiation damage in mammalian cells. Experiments designed to identify this factor have been conducted with the sulfhydryl binding agent, N-ethylmaleimide (NEM) in synchronous Chinese hamster cells. Low concentrations of NEM (0.75 μM) sensitize oxygenated Chinese hamster cells most in the late S period. The effect is primarily on the slope of the survival curve, rather than its shoulder, and the maximum sensitization factor for late S cells is about 1.6. Experiments with NEM and cysteamine indicate that NEM forms a stable complex in the cell, and thus exposure to NEM before irradiation sensitizes the cell equally well as when NEM is present during irradiation. The sensitizing effect is less the longer the interval between pretreatment with NEM and irradiation. N-ethylmaleimide also has a pronounced postirradiation effect: when given immediately after irradiation, the effec...