254 1. lODOACETATE AND lODOACETAMIDE 



in the succeeding sections, and only the specific studies on mitosis will be 

 considered here. The growth of chick embryo fibroblasts in culture was 

 found by Krontowski et al. (1932 b) to be completely suppressed by 0.05 

 mM iodoacetate, glucose utilization being simultaneously reduced 93%. 

 This concentration also prevents growth of chick embryo brain cultures, 

 while 0.02 raM iodoacetate causes fusion of the chromatin in dividing cells 

 to form a pycnotic mass (O'Connor, 1950 a). Certainly iodoacetate is one 

 of the most potent antimitotic agents among the common inhibitors. Harris 

 (1956) found 1 mM iodoacetamide to cause immediate disappearance of 

 all rat heart connective tissue cells in culture, but did not use lower con- 

 centrations. Mouse epidermal fragments in glucose medium show cells in 

 various stages of mitosis; iodoacetate at 0.1 mM completely blocks initiation 

 of new mitoses within 2 hr, and by 4 hr no cells in mitosis are visible (Bull- 

 ough and Johnson, 1951). Since mitosis here is dependent on glucose, the 

 inhibition by iodoacetate is not surprising. Gelfant (1960) continued this 

 work and showed that within 4 hr the number of mitoses is depressed 75% 

 by 0.01 mM iodoacetate. Various substrates, including pyruvate, lactate, 

 succinate, and a-ketoglutarate, cannot reverse the action of iodoacetate 

 at 0.05 mM, which almost abolishes mitosis. The survival of skin fragments, 

 as shown by outgrowth in host animals, after being incubated for long 

 periods in physiological medium, is reduced markedly by 0.1 mM iodoace- 

 tate (Medawar, 1947), indicating again the sensitivity of skin to this in- 

 hibitor. 



More detailed effects of iodoacetate on mitosis in cultures of chick bone 

 were described by A.F.W. Hughes (1950). Of all the inhibitors tested, only 

 fluoride and iodoacetate block pre-prophase activity, i.e., prevent the cells 

 from entering prophase, without affecting interphase cells or the later stages 

 of mitosis. Exposure to 0.05 mM iodoacetate prevents mitotic entry, and 

 yet 0.54-1.8 mM if added during metaphase only prolongs this stage some- 

 what without impairing the spindle and allows normal anaphase and cleav- 

 age. It requires 5.4 mM to block entry into anaphase, and if this con- 

 centration is added at anaphase, nuclear reconstruction is disturbed and 

 the nucleoli may be absent. Hughes discussed the possibility that SH agents 

 prevent spindle formation by reacting directly with the proteins involved, 

 and there is a good deal of evidence that SH groups, other than metabolic, 

 are involved in mitosis (Brachet, 1957). Erythrocytic development in chick 

 embryo blood is also very sensitive to iodoacetate, 0.0067 mM reducing 

 mitotic cells by 22% in 90 min (O'Connor, 1952). Chromosomal effects are 

 seen at this concentration and increase at higher concentrations; these con- 

 sist of swelling and pycnotic changes. No effect on interphase cells can be 

 observed. Since fluoride has quite different effects here, O'Connor postulat- 

 ed that the action of iodoacetate is not due to inhibition of carbohydrate 

 metabolism but presumably to some more direct action on the SH groups 



