14 , Applied Biophysics 



The Analytical Approach to the Study of Drug Action 



The aim of the hiochemist has primarily been the isolation and 

 analysis of the purihed components of the living cell, and consid- 

 erable information is now available concerning the structural 

 components, which are essentially lipids and proteins, and the 

 vital enzvme svstems which are intimateh' associated with these 

 components. In this connection, the physical chemist has been 

 able to offer valuable cooperation, for the organization of living 

 matter frequently takes the form of discrete celkilar fabrics or 

 membranes, and, apart from the permeability of such membranes, 

 the uptake of a drug is also influenced by the asymmetrical forces 

 resident at their surfaces of separation. Schulman and Rideal ^^ 

 have shown how it is possible to study the nature of the inter- 

 actions of drugs with the biological components of membranes 

 by means of the Adam-Langmuir trough. Lipids and proteins 

 can be spread on suitable substrates as two-dimensional films, 

 or monolayers consisting of a single layer of molecules. The 

 changes in the physical state, surface pressure, and surface poten- 

 tial of the monolayers gives an accurate measure of the associat- 

 ing forces between the biological components and the drugs which 

 are introduced into the underlying substrates. 



The ''Receptor Theory 



99 



Yet despite these ordered advances in what we might term 

 the analytical approach to the nature of drug action, the bulk 

 of existing pharmacological data can be interpreted only by 

 assuming that drugs combine with hypothetical "receptors" in the 

 living organism to produce similar or antagonistic responses. 

 When this occurs it is supposed that the drugs compete for the 

 same receptors in the surface or tissue which is the site of drug 

 action. For example, the bacteriostatic action of sulphonamide 

 drugs is neutralized by the presence of /J-aminobenzoic acid, an 

 essential metabolite which is utilized by the bacteria. Woods '*- 

 has advanced the view that the antisulphonamide activity of 



