168 MACROMOLECULAR COMPLEXES 



for disulfide groups. At anaphase, the traction fibers stained 

 strongly for both groups, while the interzonal fibers only appeared 

 to contain the sulfhydryl groups in detectable amounts. 



Studies designed to reveal quantitative fluctuations in the sulf- 

 hydryl and disulfide groups associated with protein and non-protein 

 compounds have been performed on populations of cells at various 

 stages of mitotic and meiotic divisions. The findings most often 

 quoted are those of Rapkine (1931) on the TCA-soluble fraction of 

 sea-urchin eggs. He observed a large steady drop in soluble sulf- 

 hydryl concentration after fertilization, followed by a rapid increase 

 to a maximum just prior to cleavage. He felt that his results re- 

 flected variations in the glutathione content of the cells, and pre- 

 sented an ingenious scheme in which glutathione was oxidized, with 

 the concomitant reduction of intramolecular protein disulfide bonds. 

 The latter were then reoxidized into intermolecular bonds, and 

 reduced glutathione was recovered. This was presumably related 

 to the buildup of the mitotic apparatus. Recently, Neufeld and 

 Mazia (1957) reinvestigated the problem of the non-protein sulf- 

 hydryl cycle in Strongylocentrotus purpuratus, but were unable to 

 corroborate Rapkine's data. Since then some very careful work by 

 Sakai and Dan (1959), again on sea urchins, uncovered a possible 

 explanation for this discrepancy. By carefully duplicating the ex- 

 traction procedure of Rapkine, they substantiated his original ob- 

 servations, but found that the TCA-soluble material responsible for 

 the fluctuations in sulfhydryl was not glutathione, as Rapkine had 

 supposed, but a protein that was soluble in TCA under the condi- 

 tions used by him. Plant material has also been analyzed by Stern 

 ( 1956, 1958 ) for protein and non-protein ( soluble ) sulfhydryl and 

 disulfide. He observed fluctuations in protein and soluble sulfhydryl 

 that correlated with meiosis and microspore mitosis in both Lilium 

 and Trillium. 



Some preliminary solubility studies on the mitotic apparatus iso- 

 lated directly from living material have been conducted recently 

 in Mazia's laboratory. The data make it more difficult to accept 

 disulfide bridges per se as the primary intermolecular links involved 

 in maintaining the structural integrity of the mitotic apparatus. 

 With suitable precautions, these isolated division figures can be dis- 

 solved under extremely mild conditions. They are completely 

 dispersed in water in the pH range between 8.5 and 9, while KCl 

 solutions, at neutrality, of 0.5M concentration or greater will dis- 



