J. F. DANIELLI ■ H. J. KOCH 



R. J. Goldacre. What are the relative merits of the hypothesis of protein molecules 

 contracting through pores in the membrane and that of the complete folding up of 

 the membrane and its solution in the cytoplasm together with any molecules ad- 

 sorbed onto it from outside? It seems that relatively few fibres could pass through a 

 pore, so that the same contraction pulling these fibres through would tend to cause 

 folding up of the membrane as a whole owing to the contraction of adjacent fibres 

 not passing through pores. Also would you not expect that the existence of pores 

 sufficiently large to allow significant amounts of electrolytes to get through would 

 require an electrical conductivity for the plasma membrane considerably different 

 from that found? 



J. F. Danielli. Facilitated diffusion may occur without active folding of a protein or 

 its oscillation between two states. It is sufficient for the protein to provide a polar 

 channel through the membrane. Facilitated diffusion would be converted into 

 active transport by the development of contractility of the protein. Folding of the 

 whole membrane, and its dissolution, may occur in some instances, but in others, for 

 instance the erythrocyte, such a process is most unlikely. The electrical conductivity 

 of the plasma membrane is higher than would be expected for a homogeneous 

 lipoid layer, so that the existence of a limited member of ion-permeable pores is 

 not incompatible with the membrane conductivity. 



R. D. Keynes. Have you any views as to how protein pores might achieve the remark- 

 able discrimination exhibited by cell membranes between anions and cations or 

 between sodium and potassium? 



J. F. Danielli. I should, in general, expect discrimination between sodium and 

 potassium to be possible by a mechanism involving the formation of co-ordination 

 compounds. The stereochemical properties of a co-ordinating molecule could be 

 such as to give a considerably greater stability to the compound with sodium than 

 the compound with potassium, or vice versa. 



R. J. Goldacre. Instances are known where the absorption of potassium is considerably 

 different from that of sodium. For example, Szent-Gyorgi and his co-workers have 

 isolated various myosin-like proteins from kidney, heart, brain, lung, and muscle, 

 which are characterized by a relatively high absorption power for potassium ions; 

 for myosin itself I think he found that i g. of potassium was absorbed by about 

 4,000 g. of myosin. Also in the related field of absorption on mineral surfaces, 

 potassium and sodium may behave quite differently. This difference is exploited in 

 the commercial separation of NaCl from KC1 by the froth flotation process. 



W. S. Reith. Concerning the preferential position of the potassium ion I should like 

 to mention that a nitrated polystyrene ion-exchange resin has been described in 

 the literature which possesses an unusual affinity for the potassium ion. 



N. Myant. How does the aqueous pore theory fit in with penetration of protein mole- 

 cules to the inside of cells ? 



J. F. Danielli. Proteins may in theory penetrate through polar pores. Whether they 

 will do so or not will depend upon the nature of the pores and of the proteins. One 

 would expect the process to be highly selective. 



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