THE CENTRAL PROBLEMS OF THE BIOCHEMISTRY OF CELL DIVISION 487 



seen in cells except when they are dividing. The question is whether this 

 amount of structuie protein is made as the mitotic apparatus is formed or is 

 made earlier and assembled at the time of division. For the sea urchin egg, 

 the answer seems to be that it is preformed. This was shown by H. A. 

 Went [28] by immunological means. He has demonstrated that the egg 

 before division contains all of the antigens that can be recovered from the 

 isolated mitotic apparatus. 



While such a finding, if general, would suggest that the actual formation 

 of the apparatus is a problem of assemblv and not of svnthesis, it does not 

 follow that the synthesis of structural protein for the mitotic machinery is 

 not one of the important problems of the biochemistry of cell di\ision. The 

 egg is a special case, a cell which is provided with enough proteins, includ- 

 ing enzvmes, for a long period of de\elopment and it undergoes little or 

 no net growth. In a growing population, each cell would have to provide 

 the protein for the mitotic apparatus of the next division, or at least half 

 of it if it "inherited" half from the previous di\ision. But it would be 

 important for our thinking about the control of cell division if the protein 

 of the mitotic machinerv had to be svnthesized in anticipation of a future 

 division. As Swann [31] has pointed out, the di\'ersion of proteins and 

 protein svnthesis into or from the formation of the mitotic apparatus may 

 be an interesting factor in differentiation and the control of division. 



8. Thiol chemistry and cell division 



The alchemists never succeeded in transmuting sulphur into gold, but 

 the biochemists may yet do so. It is an extraordinary fact that theories in 

 which thiols plaved a central part have been prominent in discussions of 

 the biochemistry of cell division ever since there were such discussions. 

 One need only cite Louis Rapkine, whose work on a glutathione cycle 

 during mitosis [^2] was the stimulus to much contemporary work (dis- 

 cussed bv Mazia [2^], Stern [t,^])- Among others who early felt that thiol 

 biochemistrv somehow lav at the heart of the cell division problem was 

 Hammett [34], and there were others. In recent years, the study of what 

 we in our laboratory call the "Thiology" of cell division -confessing to 

 an ingredient of faith as well as of good works in this line of study — has 

 de\eloped in a number of ways: in studies on metabolic regulations 

 associated with thiols, in studies of the relation between soluble and 

 protein SH in the dividing cell [30, 35, 36, 37], in studies on the inter- 

 ference with cell division bv SH compounds [25, 3S], in the demonstration 

 of the participation of interesting sulphur-containing nucleotidepolypetide 

 complexes in cell division in algae [39] and in observations on a specific 

 role of sulphur-containing amino acids in the synchronization of division 

 in algae [40]. 



