J. F. DANIELLI 



a good deal of water, as is the case with protein crystals, and extensive hydrogen 

 bonding between the protein chains will give it a unique character. The properties, 

 of this polar pore will include : 



(i) ready permeability to small hydrogen-bond-forming molecules such as water 

 and formamide. 



(ii) if the protein component is positively charged, e.g. if it were haemoglobin, it 

 would be selectively permeable to small anions, and thus provide the facilitated 

 diffusion mechanism in red cells suggested by Davson. If negatively charged it would 

 be selectively permeable to small cations. 



(iii) to larger polar molecules the pore would be permeable only if the structure 

 and configuration of the molecule conformed to the structure of the pore. 



(iv) passage through such a pore need not occur by movement of the penetrating 

 molecule only. We can envisage the protein components of such pores oscillating 

 between different configurations. Examples of such oscillations are found in reversibly 

 denatured proteins. Such oscillations may assist in conveying molecules through the 

 membrane. 



(v) a pore of this nature offers a basis for working out possible modes of action of 

 hormones, such as insulin and 'growth' hormone, which are concerned in transfer 

 processes. 



(vi) a pore of this character provides a mechanism which will permit proteins to 

 pass through plasma membranes. The possibility of such passage would depend upon 

 the specific configurations of the proteins of the pore and of the permeating protein, 

 and a mechanism of this type may account for selective permeability to proteins of 

 the type reported by Brambell and Hemmings for the passage of antibodies through 

 the intestinal wall, etc. 



(vii) pores of this character would not only exert the selectivity characteristic of 

 facilitated diffusion, but would also be susceptible to the action of enzyme poisons,, 

 such as those mentioned in Table II. 



In short, a pore structure of this type appears to provide an excellent working- 

 hypothesis for study in connexion with facilitated diffusion. The components of the 

 pore need not be entirely restricted to protein, but might include nucleic acids, poly- 

 saccharides, etc. This conception has the additional advantage that by simple exten- 

 sion the mechanism of facilitated diffusion becomes a mechanism of active transport. 

 Where movement of the penetrating species is determined by the kinetic energy of 

 the penetrating molecules themselves, or by the oscillation of a protein between 

 alternative structures under the influence of thermal agitation, the process is facili- 

 tated diffusion. But if the movement is determined by a contraction-expansion, or 

 oscillation, impressed upon a protein by the energy released by the enzymic action 

 of that protein, then we have active transfer. Thus Goldacre's (1952) concept of the 

 importance of contractile proteins in active transport becomes logically connected 

 with the mechanism deduced for facilitated diffusion. 



As was mentioned earlier, the permeation of glucose which is insulin-dependent 

 need not be active transfer but may be facilitated diffusion, with glucohexokinase 

 present at the inner end of the facilitating pore. Alternatively, hexokinase might be 

 one of the pore proteins, with the phosphorylative mechanism at the inner end of 



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