tion of soluble — SH occurs during the beginning stages of formation of 

 the spindle gel as the result of glutathione being oxidized in the reduc- 

 tion of the intramolecular — SS — bonds of the spindle protein to fixed 

 — SH groups. The rise in soluble — SH accompanying the final stages of 

 gelation of the spindle is the result of the reduction of glutathione ac- 

 companying the oxidation of the fixed — SH of the spindle protein to 

 form intermolecular — SS — linkages. 



While the variations in soluble — SH observed to occur during cell 

 division seem well documented, it is questionable that such changes can 

 be interpreted as evidence for operation of an oxidation-reduction cycle 

 specifically involving glutathione. Several studies have demonstrated that 



(I) 



(ID 



r^ 



Y-SH 



4- 



2GSH 



Hs-n 



V^ 



hS SG 



GS-S-l 



vv 



r>SH HS 



L/-S-SG GS-S-LJ 



r>s— s-p 



2GSH 



Figure 6-6. Schematic Representation of Alternative Mechanism of Poly- 

 merization of the Protein of the Mitotic Apparatus. In this scheme oxidized 

 glutathione would not be detected. (From Mazia, D., 1955. "The Organiza- 

 tion of the Mitotic Apparatus," Symp. Soc. Exptl. Biol, 9, Fig. 8, p. 349.) 



the amount of oxidized glutathione detectable in the sea urchin egg is 

 small and constant in value, and that when reductions in reduced gluta- 

 thione do occur they are not accompanied by corresponding increases 

 in the amount of oxidized glutathione (Bolognari, 1952; Infantellina 

 and LaGrutta, 1948). To account for this observation, Mazia (1955) 

 has proposed an alternate mechanism for the gelation of the spindle 

 protein, which involves a binding of the oxidized form of glutathione to 

 the protein of the spindle (Figure 6-6). In this scheme, oxidized gluta- 

 thione would not be detected, and would function in the redox reaction 

 to produce intermolecular — SS — linkages. Barron (1951) has pointed 

 out that variations in soluble — SH during cell division would undoubt- 

 edly affect the redox potential of the whole cell and result in marked 

 changes in the activities of various enzymes. Swann (1957) suggested 

 that since many respiratory enzymes are sensitive to oxidation and block- 

 ing of their — SH groups, respiration should vary with the amount of 

 soluble — SH, being minimal around the beginning of mitosis. Recent 



148 / CHAPTER 6 



