Ionizing Radiations and Enzymes 33 



mode of action of radiation which will have to be considered 

 when attempting to correlate the results with the structural 

 organization and the metabolic activities of cells. 



(1) Can one assume that the dilution effect may operate 

 inside a cell? In other words, are there intermicellar spaces 

 through which enzyme molecules diffuse from storage depots 

 when called upon by metabolic requirements of the cell? 



(2) Are these intermicellar spaces in the inhomogeneous 

 cell structure filled with high concentrations of protective 

 substances? 



(3) Is there a spatial separation between substrates and 

 surface-bound enzymes which may involve an action of radia- 

 tion on substrates in transit? 



(4) Should one consider not a depletion of stored enzymes 

 but rather a decrease of the functional fraction of enzymes 

 which, by slowing down reaction velocities and possibly also 

 by the initiation of non-enzymic chain reactions, disorganizes 

 the delicate sequence of metabolic steps? 



(5) Can one expect from an analysis of tissue extracts or 

 homogenates irradiated as such, or made from irradiated 

 tissues, any answer to the question of the participation of 

 enzymes in biological radiation effects? 



Answers to all these questions will depend on the degree of 

 knowledge of the internal organization of cells at the sub- 

 microscopic level, and I hope that the discussion will clarify 

 some of the issues raised. 



REFERENCES 



Anderson, R. S. (1954). Brit. J. Radiol., 27, 56. 



Aronson, D., Mee, L., and Smith, C. L. (1955). IV Int. Conf. Radiobiol. 



Edinburgh : Oliver & Boyd. 

 Barron, E. S. G., and Dickman, S. (1949). J. gen. Physiol., 32, 595. 

 Barron, E. S. G., Dickman, S., Muntz, J. A., and Singer, T. P. (1949). 



J. gen. Physiol., 32, 537. 

 CoLLiNSON, E., Dainton, F. S., and Holmes, B. (1950). Nature, Lond., 



165, 266. 

 Dale, W. M. (1940). Biochem. J., 34, 1367. 

 Dale, W. M. (1942). Biochem. J., 36, 80. 

 Dale, W. M. (1947). Brit. J. Radiol., SuppL, 1, 46. 



BAD. 3 



