EFFECTS ON MITOSIS AND GROWTH 365 



is nontoxic to S. avrcvs, E. coli. and Pseudomouas sp.. but when applied 

 a few minutes before irradiation it increases the lethal effect both aerobically 

 and anaerobically. Addition of iV-ethylmaleimide after the irradiation does 

 not alter the result. Bridges thinks that the inhibitor and the radiation must 

 act simultaneously, and ])Ostulates that lY-ethylmaleimide may react with 

 some short-lived molecule or intermediate produced by the radiation, or 

 with SH groups formed by the splitting of disulfide bonds by the radiation. 

 Lynch and Howard-Flanders (1962) confirmed this effect in Shigella sonnet 

 for 0.2 mM iV-ethylmaleimide and found that the SH content of the cells 

 is reduced around 75% within 30 min. It would be interesting to know if 

 iV-ethylmaleimide alters the response of simpler systems to irradiation. 

 Vaccinia virus is quite readily inactivated by 0.1 mM A^-ethylmaleimide and, 

 as with the mercurials and iodoacetamide, the action is not to prevent at- 

 tachment to the host cell but the release of nucleic acids within the cells 

 (Allison, 1962). It may be noted that iV-butylmaleimide has been intro- 

 duced commercially as a disinfectant. ^ 



Plant growth can be inhibited by A'-ethylmaleimide and van Overbeek 

 et al. (1955) considered it to be an auxin antagonist, while Niedergang- 

 Kamien and Leopold (1957) showed that at 0.01-1 mM it reduces auxin 

 transport. Microspore mitosis in cultured lily anthers is inhibited by 2 mM 

 A-ethylmaleimide and since there is a 30% decrease in thiol content it 

 was assumed that the inhibition is attributable to this, resumption of mi- 

 tosis after 4-5 days being due to the biosynthesis of new thiols (Stern. 

 1959). Nothing is known of the inhibiting effects of A-ethylmaleimide on 

 tumor cells, but Belkin and Hardy (1961) observed that at 0.1 mM there 

 is blebbing of Sarcoma 37 ascites cells, this usually being of the scalloped 

 type, although in other tumor cells different blebbing patterns were seen. 

 Such a blebbing reaction also occurs in vivo following the injection of A^- 

 ethylmaleimide. Blebbing is generally considered to be a reaction brought 

 about in the membranes as a result of SH group reaction, this altering the 

 membrane structure and water permeability. 



