20 Applied Biophysics 



and Is apparently more marked in nerve trunks than in white 

 matter. 



The Pattern of Lipid-Proteiii-Enzyme Relationship 



These diverse observations stress the close relationship be- 

 tween the lipids and proteins in organized tissues. We may 

 imagine that the lipids exert a protective action on the protein 

 structural components of membranes. Baker, Harrison, Miller, 

 and W^exler ^ have found that the action of synthetic detergents 

 on bacteria is inhibited by the presence of phospholipids, and 

 it is supposed that the denaturation of the proteins of the bac- 

 terial membrane is prevented by the lipids. Perhaps a similar 

 protective action may account for the resistance of the cell 

 membrane or ghost to the digestive action of pepsin and trypsin, 

 but Ballentine and Parpart '" point out that this may depend on 

 the resistant nature of the protein itself, and have suggested 

 that the structural proteins of the erythrocytes are sclero- 

 proteins, possibly of the albuminoid type. 



It is permissible to conclude from these examples that, 

 although we have not yet obtained a coherent pattern of the way 

 in which lipids, proteins, and enzymes are organized in living 

 systems, the shape of this pattern is gradually being resolved. 

 The biologist holds the initiative in this respect, for, as he 

 extends the range of his biological systems and his technical 

 resources for examining these systems, he can select model 

 systems to assist in the elucidations of the complexities of mem- 

 brane structure, instead of selecting his biological systems to 

 elucidate complexities in model systems which are of uncertain 

 biological significance. ^Vhat may we profitably look for when 

 we encounter a natural membrane which we have not examined ? 

 We can visualize a structural framework or fabric composed of 

 a relatively resistant lipo-protein complex in which the com- 

 ponents swell in fat solvents or water but are not readily dis- 

 solved in these media. Incorporated functionally in this frame- 

 work are labile lipids and proteins or lipo-proteins, and possibly 

 enzymes which can be more readily displaced or removed from 



