138 THE BIOSYNTHESIS OF PROTEINS 



property of transferring electrons to cytochrome, and it is later changed 

 into the L-specific enzyme. The complete transformation takes more time 

 than the synthesis of cytochrome oxidase or catalase, which seem to behave 

 according to the classical scheme of induced enzyme synthesis (Nygaard, 

 1960). 



5. Permeases and Efizyme Synthesis 



Certain exogeneous inducers induce enzyme synthesis only if they can 

 enter the bacterium and if their concentration at their site of action is 

 sufficient. Small molecular weight substances sometimes can enter a cell 

 by diffusion. More complex processes are involved in most cases; the 

 'permeability' of cells is very specific and cannot in any way be compared 

 to the old misleading model of the semipermeable membrane which retains 

 certain molecular species and allows water and other substances to diffuse 

 freely. Some cells absorb and concentrate proteins readily but are com- 

 pletely impermeable to glycin or succinic acid for instance. The proteins 

 are taken up by a complex process of pinocytosis. Moreover, all types of 

 cells are able to concentrate various substances, like amino acids or sugars, 

 from an outer dilute solution. Thus E. colt grown on lactose is able to 

 absorb and concentrate several j8-galactosides (Monod, 1956; Cohen and 

 Monod, 1957); the concentration inside the bacterium can be a hundred 

 times the outer concentration, and its maintenance requires a continuous 

 expenditure of energy. Azide, which prevents phosphorylations, inhibits 

 the concentration mechanism. The accumulated galactosides seem to be 

 free within the bacterium and this considerably increases the inner osmotic 

 pressure; if the cell wall is damaged by enzyme action, its mechanical 

 strength is reduced, and the internal osmotic pressure resulting from the 

 accumulation of the galactosides can be high enough to cause the rupture of 

 the bacteria (Rickenberg et al., 1956; Sistrom, 1958). This permeation 

 system, which was called 'permease', is not present in bacteria which have 

 not been in contact with galactosides; it is an inducible system which 

 responds to the same inducers as /3-galactosidase. 



When a non-adapted bacterium is confronted with an adequate galacto- 

 side, some galactoside enters the cell by diffusion, and there is a certain 

 probability that the formation of one molecule of permease is induced. 

 Once this molecule is formed, the internal concentration of galactoside 

 increases, and this results in the induction of more permease and of j8- 

 galactosidase at the same time (Novick and Weiner, 1957). The permease — 

 the chemical nature of which is unknown — thus influences the induced 

 formation of the enzyme j3-galactosidase in an indirect way, by concentrat- 

 ing the inducer of the enzyme within the cell. The kinetics of j3-galactosi- 

 dase formation actually reflects that of the formation of permease. 



Rather complex consequences of this situation can be observed. If 



