MECHANISM OF ANTIBODY FORMATION 97 



differences in the rates of the metabohsm of various structurally related 

 substrates. There is no evidence as to the presence of individual 

 enzymes for each of the class of substrates which possess the same 

 enzyme specific active group. Thus, according to the formulation of 

 Weidennagen (1940), "there is no special key for each lock but a 

 master key for a group of locks." Glucose, mannose, fructose, etc.; 

 arginine, creatine, etc. possessing, respectively, the same configuration, 

 would be metabolized by the same enzyme. Several dipeptides com- 

 posed of different amino acids are hydrolyzed by Anson's crystalline 

 carboxypeptidase, etc. In this connection the concept of Monod 

 (1943, 1944, 1945, 1947) is of interest. According to him, all the 

 adaptive and constitutive carbohydrate-attacking enzymes in bacteria 

 may depend on a common mechanism of synthesis, or, more precisely, 

 on a common precursor. The mutual-exclusion effect results from a 

 competitive interaction of the substrates for the 'preenzymes or the 

 common precursor. This concept likewise agrees with our view 

 that under the influence of a substrate the synthesis of a new specific 

 enzyme protein does not occur. 



On the other hand, Spiegelman, et al. (1947) postulate that enzyme 

 adaptation involves protein modification requiring energy-yielding 

 metabolic reactions. Such assumptions cannot be accepted as valid un- 

 til the postulated pre-protein and the enzyme derived therefrom are 

 characterized, and the energy relationships of the chemical reactions 

 leading from the former to the latter are established. The principal 

 justification for the claim of the formation of "adaptive enzymes" 

 seems therefore to lie in the fact that the enzyme activity for a certain 

 substrate (for example, galactose)* disappears or is greatly diminished 



*On the basis of the results of recent studies we are now able to gain an insight 

 into the mechanism of the fermentation of galactose by yeast. Various steps involved 

 in galactose fermentation are described as follows: 



Galactose -f ATP >- galactose- 1 -phosphate + ADP 



I 



glucose— 1 —phosphate >- Galactose— 1 —phosphate y glucose— 6— phosphate 



II III 



According to Wilkinson (1949) the first step (reaction I) in galactose fermenta- 

 tion by Dutch Top yeast is the transference of the terminal phosphate group from 

 adenosine triphosphate (ATP) to galactose to give galactose- 1 -phosphate. (There 

 was no evidence for the accumulation of galactose- 1 -phosphate during the pre- 

 adaptive period.) The enzyme catalyzing this reaction is activated by Mg++ and by 

 cysteine, and is named galactokinase. Since galactose is fermented via fructose- 1,6- 

 diphosphate, the question of how the glactose-1 -phosphate is converted to glucose- 

 1-phosphate (reaction II) arises. According to Caputto et al. (1950), the reaction II 



