Chairman's Introduction 



Bernard D. Davis 



Department of Bacteriology and InuniDiology, 



Harvard Medical School, 



Boston, Mass., U.S.A. 



In analyzing metabolic pathways it has long been profitable to approach 

 the cell as though it were merely a bag of enzymes. Recent years, however, 

 have seen a broad and rapid increase of interest in the properties of cell 

 membranes. Two of the reasons have already been prominent in this 

 Symposium : the intracellular detail revealed bv the electron microscope, 

 and the dependence of mitochondrial function on an organized relation of 

 enzymes to membranes. But probably the most dramatic contribution has 

 come from bacteria : not only do these cells also possess a variety of specific 

 transport systems, but these systems have been found to respond, like the 

 intracellular enzymes, to control by induction, repression, and mutation. 

 This development provides compelling further evidence for the realitv 

 and the importance of specific transport svstems; even more, it offers 

 hope of a new approach to their understanding. 



The evidence for specific transport systems is rather indirect, com- 

 pared with that available for most biochemical entities. Hence inferences 

 involving them have often met with scepticism. Indeed, the various kinds 

 of evidence available for these systems are each usually capable of alter- 

 native interpretations, and it is only the convergence of a number of lines 

 of evidence that has now led to quite general acceptance. Since these 

 various kinds of evidence may not all be familiar to biochemists, and since 

 the unfortunate absence of two scheduled speakers has given us extra time, 

 I shall try to summarize the evidence briefly. 



But first I would like to devote a few minutes to historical and to 

 comparati\e considerations. For most of the w^ork on permeability in 

 bacteria has developed autochthonously, rather than as a product of 

 laboratories concerned primarily with permeability; hence it has tended 

 somewhat to neglect the unity of biology at a molecular level, which so 

 dominates our thinking throughout biochemistry today.* 



* In this connection, howevtr, it should be noted that electron microscopy 

 reveals for the cytoplasmic membrane of bacteria only a single dark and a single 

 light layer, whereas the membranes of all other organisms studied have shown, 

 following similar fixation, a light layer between two dark layers. Furthermore, 



