TEMPERATURE-PRESSURE STUDIES ON THE ROLE 

 OF SOL-GEL REACTIONS IN CELL DIVISION^ 



Douglas AIarslaxd, Washington Square College, 

 New York University, New York City 



R. 



.EVERSiBLE sol-gel transformations have been observed in various cells 

 for many years. It was not until 1926, however, starting with Mast's 

 classical work on amoeboid movement (25), that the functional signifi- 

 cance of these transformations began to be understood. Now, about thirty 

 years later, there is considerable evidence which indicates that protoplas- 

 mic gel structures are potentially contractile. The gelational process seems 

 to represent a mechanism which enables the cell to perform mechanical 

 work. The purpose of this paper is to review the evidence, with special 

 reference to the furrowing movements (cytokinesis) in animal cells. It 

 seems probable that the development of mechanical energy by muscle 

 tissues represents a related phenomenon, but the present discussion will 

 be concerned primarily with contractile processes in the less highly 

 specialized egg cell. 



A priori, the development of contractility in an essentially fluid system, 

 such as protoplasm, would seem to presuppose the formation of some 

 kind of gel structure. If, as seems likely, the contractile force originates 

 from the folding of elongate protein molecules or molecular aggregates, 

 it is difficult to see how such a folding could be effective in performing 

 work unless the extended protein units were interlinked, forming a continu- 

 ous and fairly extensive system throughout the cell (5) . Subsequent to fold- 

 ing, moreover, when the extended units have assumed a more globular form, 

 the system can revert to the sol condition, merely by the loosening of the 

 intermolecular bonds. The final dimensions, after folding in some gels, 

 may represent a rather small fraction (about 10%) of the original volume 

 of the gel as a whole. Thus the work performed during contraction may 

 be considerable. Moreover, since the primary orientation of the elongate 

 protein components may not be unidirectional, such systems need not 

 display anisotropy, either in the expanded or contracted state. 



Gel Structure in Relation to Pressure and Temperature. The early 

 work of Brown (1) on Arbacia eggs and of Brown and Marsland (2) on 

 two species of amoeba, showed that a drastic weakening and finally a 



^ Work supported by grant series C807 from the National Cancer Institute, U. S. 

 Public Health Service. 



Ill 



