APPROACHES TO THE ANALYSIS OF SPECIFIC MEMBRANE TRANSPORT 583 



coli is not. In general, however, bacterial plasma membranes behave in the 

 way expected of the type of thin hpid fihii postulated by Overton [6] in his 

 lipid membrane concept at the beginning of this century [7-13, and see 4]. 



The question naturally arises — and this has been discussed ever since 

 the lipid membrane concept was introduced — if the membrane is im- 

 permeable to the nutrients of the medium, how do they get into the cell 

 during metabolism and growth ? The kinetic studies of glutamate and 

 lysine transport in streptococci and staphylococci in which I was impli- 

 cated in Dr. Gale's laboratory [14, 15, 5], and the detailed kinetic analysis 

 of phosphate translocation in staphylococci which I undertook shortly 

 after [7, 16-18], led us to the conclusion that transport systems of high 

 substrate specificity, exhibiting kinetic features indistinguishable from 

 those of the classical enzyme and carrier systems of biochemistrv, must be 

 responsible for allowing the nutrients to enter the metabolic svstems of 

 bacteria. This conception of the very close relationship between transport 

 and metabolism in bacteria has been confirmed by the more recent studies 

 in my laboratory on sugar and carboxylic acid transport [see 2, 3, 4, 19, 13], 

 some aspects of which I shall describe later in this paper. The kinetic 

 studies of galactoside and amino acid uptake in Esclierichia coli carried out 

 by Monod and his collaborators [20-22] also support our view of the 

 intimate relationship between the phenomena of transport and metabolism 

 — although, the interpretation which Monod and his collaborators placed 

 on these studies was fundamentally difl^erent from ours [i]. According to 

 the recent work on the kinetics of galactoside uptake into Escherichia coli 

 described by Kepes [23], the "galactoside permease" system is identical 

 in principle to the hypothetical system originally suggested for the passage 

 of " glutamate " into streptococci through the enzvme-catalvzed conversion 

 of glutamate to glutamine on the cell surface and ditfusion of glutamine 

 through the membrane [5]. This is satisfactory in demonstrating the 

 present consensus of opinion as to the most elementarv types of molecular 

 mechanism that could be involved in specific membrane transport; but it 

 also shows how loose and unsatisfactory the use of the word "permease" 

 has become, even amongst different workers at the Pasteur Institute. I feel, 

 therefore, that I must digress for a moment to say that I am inclined to 

 associate myself with the suggestion that Dr. Davis made in his introduc- 

 tion to this session of the Symposium, that the word "permease" might 

 best be abandoned. I advocated in the past that the word "permease" 

 should be strictly used to mean a protein catalyst of facilitated diffusion 

 [2-4], and perhaps this use might still be introduced if such a catalyst 

 should be found to exist. 



As Dr. Davis mentioned in his introduction, Kogut and Podoski [24], 

 Barrett et al. [25], Green and Davis [26], and Monod and his collaborators 

 [21] discovered that the catalysts of the entry of certain carboxylic acids 



