94 ELECTROLYTES IN BIOLOGICAL SYSTEMS 



that the peripheral zone is less than 500 A thick, assuming uniform distribution. 

 It would be correspondingly thicker if restricted to only a portion of the sur- 

 face. 



Conway (4) also comes to the conclusion that there is an outer metabolic 

 zone in the yeast cell, based on the exchange of K+ and H+ during metabolism 

 of glucose, the resultant changes in pH of the medium and of the cytoplasm, 

 and also on volume of distribution studies. He suggests that certain redox 

 reactions in cell metabolism are located in the outer zone, reactions which are 

 the direct source of H+ for exchange with K"*" of the medium, 



RELATIONSHIP OF CELL SURFACE TO ELECTROLYTE METABOLISM 



In the preceding sections, a summary has been presented of the available 

 data concerning two aspects of electrolyte metabolism in yeast, the transfer 

 of ions into or out of the cell that occur during active metabolism, and the 

 influence of ions on the rate of metabolism. It has also been pointed out that 

 the latter phenomena may in large part be associated with the presence in the 

 periphery of the cell of glycolytic reactions. The present section represents an 

 attempt to crystallize the information and to present an obviously oversimpli- 

 fied picture of the events that may occur when electrolytes interact with the 

 yeast cell. It is presented with the full realization that it fails to fully explain 

 many phenomena, and that it is based in part on inadequate and often con- 

 fusing information. However, it has the merits of a working hypothesis, and 

 it does stress the functional properties of the cell surface. In the author's opin- 

 ion, the cell surface has been too long regarded as a static or retaining mem- 

 brane, with no biochemical functions. As with most theories, the present one 

 is only partly the product of the author's own imagination. Many ideas are 

 borrowed, consciously or unconsciously from the work of others. For example, 

 the general concept of energy-coupled carrier-systems has been discussed by 

 many in the field of ion-transport. Specifically, in the case of ion transport in 

 yeast, Conway and his collaborators (5, 4) have carried out a great deal of 

 experimental work and he has put forth a theory of ion transfer which must 

 be seriously considered. 



In its simplest form the theory supposes that the yeast cell is a two compart- 

 ment system with respect to electrolytes. There is an outer compartment which 

 lies at the periphery of the cell, but which constitutes only a small fraction of 

 the cell, and an inner compartment which contains the bulk of the cellular 

 contents. The outer compartment is separated from the medium by a membrane 

 permeable to monovalent cations but relatively impermeable to bivalent cat- 

 ions and to anions because of its fi.xed negative charges, and from the inner 

 compartment by a membrane which is relatively impermeable to both cations 

 and anions. The outer compartment contains the glycolytic machinery of the 

 cell, including all of the necessary enzymes bound in structural units. The 



