APPROACHES TO THE ANALYSIS OF SPECIFIC MEMBRANE TRANSPORT 603 



recognizable membranes, it may remain more or less intact, but rougher treatment 

 makes it fall to pieces. Standing midway between the cytologist and the biochemist, 

 we may presume that the "pieces " (of the cytologist) are the "particles " or groups 

 of "particles" (of the biochemist). I think that we need to become as interested 

 in the substratum (or locational) specificities of enzymes as we have been in their 

 substrate specificities; and the elegant work on mitochondrial structure which 

 Dr. Lehninger described earlier in this symposium is clearly moving in this 

 direction. To take the analysis of the jig-saw organization of the plasma membrane 

 and other membrane complexes further will require a great collaborative effort 

 between biochemist and cytologist. Perhaps one of the most important problems 

 to settle at the present stage is whether there is a general substratum substance 

 which represents the mechanical matrix of the membrane and acts as the locator 

 for the enzymes and carrier proteins, or whether the individual molecules of the 

 enzymes, carriers, lipids and other components of the complex represent the 

 substrata for each other and share the responsibility for structural (locational) and 

 catalytic properties of the membrane fabric. 



This is a very difficult problem, and as I have already pointed out, it may well 

 be impossible to make real progress until we have learned to study the material of 

 natural membranes in anisotropic /// vitro systems. Perhaps Dr. Albertsson's 

 pohTner systems would be helpful for this purpose. We discussed this privately 

 the other day, for it struck me that the anisotropic properties of the interface 

 between the two aqueous polymer phases might be varied at will over quite a wide 

 range. Such a system might prove to be useful for studying the behaviour of 

 biologically active molecules under anisotropic conditions, and might serve as a 

 starting point for setting up reconstituted membrane systems in vitro. 



