126 A SYMPOSIUM ON RESPIRATORY ENZYMES 



cal. The work that has been done in this field leaves no doubt that 

 we are dealing with real enzymes, which, after bringing about the 

 dehydrogenation of substrate under biological conditions, are un- 

 changed. Furthermore, at the moment when they exhibit their 

 activity, the nicotinamide nucleotide is combined with its specific 

 protein just as the riboflavin nucleotide is combined with its specific 

 protein. That we deal in the one case with a relatively stable linkage 

 and in the other with a very unstable one is only a difference in 

 degree. Hence a change of the whole nomenclature would seem to 

 be unnecessary and would probably increase the confusion in this 

 field. 



The physiological reoxidation of the reduced coenzymes is 

 brought about by the oxidized form of the metabolites listed in 

 Table 7, as, for example, acetaldehyde in fermentation or pyruvic 

 acid in glycolysis. In other instances the dihydrocoenzymes are re- 

 oxidized by alloxazine proteids such as diaphorase (84), coenzyme 

 factor (85), cytochrome c reductase (38), or the enzyme recently 

 detected by Altschul, Persky, and Hogness (86). 



Spectrophometric Methods 



In studying the function of the nicotinamide nucleotide enzymes 

 we have been greatly aided by the spectrophometric methods de- 

 veloped by Warburg. The basis is the appearance of an absorption 

 band at 340 m\}. when the codehydrogenases are reduced. This 

 absorption band disappears upon reoxidation. Under proper ex- 

 perimental conditions the concentration of coenzyme or apoenzyme, 

 the substrate and acceptor specificity of the dehydrogenases, and 

 the speed of reactions can be studied, as has been done in some 

 laboratories, notably those of Warburg, Euler, and Meyerhof (lb, 

 i; 53). 



As an example the action of the reducing and the oxidizing 

 fermentation system may be given (44). See Figure 3. 



Biosynthesis of the Codehydrogenases 



In view of the relatively complicated configuration of the code- 

 hydrogenases and of their nucleotide character, it is improbable that 

 a satisfactory synthesis will be obtained by present-day methods of 

 organic chemistry. Therefore experiments designed to carry out a 

 biosynthesis from the structural units are very important from a 

 practical point of view. 



Mention may be made first of the experiments dealing with the 



