174 MACROMOLECULAR COMPLEXES 



ponent and the precursor-2 component were the only or major 

 antigens detectable. 



At this point, some speculation about the ubiquitous intracellular 

 distribution of the precursor- 1 component may be profitable. The 

 much less studied precursor-2 component will be ignored, but not 

 forgotten, in this discussion. There is little doubt that the precur- 

 sor-! component can exist in three "states." It is present in a "solu- 

 ble" as well as in an insoluble form in the unfertilized egg, and is 

 an important constituent of the mitotic apparatus. One can imagine 

 a dynamic equilibrium to exist among the three "states" of the 

 precursor- 1 component. The insoluble fraction would represent the 

 major pool of precursor- 1 component, being converted into the solu- 

 ble form as an intermediate step before its incorporation into 

 the mitotic apparatus. An interesting consequence could be that the 

 level of the "soluble" pool would remain unchanged during the 

 formation of the mitotic apparatus and might or might not be 

 greatly reduced when the mitotic apparatus is fullv formed. There- 

 fore, analysis of the "soluble" fraction for the precursor-1 component 

 during development from the unfertilized egg to the two-celled 

 stage would not reveal the fluctuations necessary to account for the 

 amount incorporated into the mitotic apparatus. 



Kane and Hersh (1959) describe some experiments that mav 

 have a bearing on the proposed interrelationships among the three 

 "states" of the precursor-1 component. Ultracentrifugal studies on 

 the soluble fraction of different stages from the unfertilized egg to 

 the two-cell stage, in Arhacia, revealed a component whose concen- 

 tration decreased with time and was undetectable at metaphase. It 

 reappeared after cleavage. At the time, it was speculated (Mazia, 

 1957 ) that this behavior reflected the incorporation of soluble struc- 

 tural units into the developing mitotic apparatus. These analyses 

 had been conducted on extracts obtained from ethanol-preserved 

 material. When the experiment was repeated on S. purpuratus, no 

 change in any component was detected that could be correlated 

 with the buildup of the mitotic apparatus. Again, ethanol-preserved 

 material had been used. For this reason, their experiments cannot 

 be compared directly with the immunochemical data presented on 

 the distribution of the precursor-1 component among the xarious 

 fractions obtained by fractionation of living eggs in isotonic non- 

 electrolyte medium. However, their results are sufficiently con- 

 sistent within themselves, so that the observed differences between 



