100 OXIDATION-REDUCTION POTENTIALS 



it the reactants it requires and has removed from it the waste products of metaboHsm. 

 The bacterial cell on the other hand has to make its own conditions suitable for carry- 

 ing out metabolic reactions, it is faced with the problem of collecting up the reactants 

 from the medium in suitable quantity and it has no specialised colleagues to carry out 

 syntheses or reactions for which it is not suited. 



The accumulation of such compounds as glutamic acid has been shown by Gale 

 to occur in bacteria ; but what can we visualise in the case of large molecules. It is 

 hardly conceivable that molecules as large as starch and some proteins can permeate 

 through the cell membrane. Surely they must undergo breakdown at the bacterial 

 surface. Again the lysis of erythrocytes by bacteria from which no soluble haemolysin 

 can be isolated must take place by the agency of the surface of the bacterium. One 

 advantage of considering the surface activity theory is that specific absorptive effects 

 at the cell surface can explain some of the specificities of bacterial actions and cut 

 down to some extent the already enormous numbers of different enzymes that must 

 be postulated to explain the many specific reactions observed. 



How is one to visualise bacterial glycolysis for example ? Let us assume that 

 something very like the muscle glycolytic sequence occurs in bacterial cultures and 

 there is much evidence that some of the steps are similar. In the rapid breakdown 

 by one bacterium of millions of molecules of glucose each minute it is not easy to 

 think of the glucose diffusing into a cell, being converted to hexose-6-phosphate and 

 then diffusing out again. Then the bacterium would have to wait for molecules of 

 hexose-6-phosphate to diffuse in again and having effected the transformation to the 

 Neuberg ester again lose the reactant by diffusion. The only explanation would seem 

 to be a mass production system in which the relevant enzymes are suitably situated 

 in the cell and the metabolites pass along the row of enzymes on a conveyor belt 

 principle so that each enzyme system in turn will produce its transformation and pass 

 the product on to the next enzyme. Presumably there must be some preferential 

 affinity by an enzyme for its specific substrate. It seems highly probable that much 

 must occur at the bacterial surface, taken in its widest sense and representing layers 

 of combined and inter-adsorbed proteins, nucleic acids and lipins. 



It is difficult to think about the problems of the bacterial cell without a diagram- 

 matic picture which is an aid to the visualisation of the mechanisms that have to be 

 explained. For this purpose the diagram below has been constructed, but it is 

 reproduced only with great trepidation. It does not represent the author's definitive 

 views on the subject, but it does indicate the way in which a chemical engineer might 

 tackle the problem if he were presented with the sort of data we now have available. 



Let us try to trace the path of a molecule of glucose in the culture medium that is 

 due for breaking down. First it has to come into contact with the phosphorylating 

 system, and for this it has to find its way through the sticky capsule of the bacterium 

 (if it is a capsulated organism), presumably by diffusion. Then the cell wall, generally 

 a relatively sturdy structure in most views, has to be traversed. There is controversy 

 here about the mechanism of transport through the cell wall. Is this a simple osmotic 

 effect ? Is the cell wall a semi-permeable membrane with interstices large enough to 

 let through molecules of glucose (and even soluble enzyme proteins) ? Even if it is 

 diffusion througli the pores of a membrane, free energy must be supplied in some cases 

 since there may be ten times the concentration of glutamic acid, for example, inside 



