METABOLIC FUNCTIONS OF B VITAMINS 237 



ing the way the electric currents resulting from localized changes in these 

 potentials are controlled. Studies on the enzymatic capacities of tissues 

 in which the electrical potentials are pronounced (nerves and the electric 

 organs of electric eels and fish) established a correlation between the 

 acetylcholine metabolism of these tissues and the electrical potentials 

 which they could develop. 51 On the basis of considerable evidence it was 

 postulated that the electric current responsible for the conduction of 

 impulses in nerve 51 and muscle fibers 52 was due to the release and 

 hydrolysis of acetylcholine, a process which was believed to cause a local 

 change in the permeability of the cell membrane and a resultant flow of 

 the "action current," and that the energy released during the hydrolysis 

 of acetylcholine originally was derived from the high-energy phosphate 

 bonds utilized in the synthesis of acetylcholine. Since this postulate was 

 advanced, convincing arguments against such a direct involvement of 

 acetylcholine in conduction have been offered; 53 its exact function in 

 nervous and electric tissue is still open to question. 



One of the first functions demonstrated for pantothenic acid was the 

 requirement for its coenzyme (coenzyme A) in choline acetylase, 54 the 

 enzyme catalyzing the reaction in which choline is acetylated by the 

 phosphoryl-acetyl intermediate derived either (1) from the oxidative 

 decarboxylation of pyruvic acid (thiamine pyrophosphate essential) or 

 (2) from the direct phosphorylation of acetic acid (coenzyme A required) . 

 Hence, these two coenzymes are of specific importance for the functioning 

 of cells where conduction takes place. 



Radiant Energy. The biological conversion of radiant energy to chem- 

 ical energy by the reduction of carbon dioxide (photosynthesis) and the 

 reverse process, the emission of radiant energy during biological oxida- 

 tions of organic substrates (bioluminescence) , are the result of two proc- 

 esses whose mechanisms are entirely unrelated. The chemical reactions 

 responsible for the latter phenomena have been well established, but the 

 former process, which is indispensable from the standpoint of the economy 

 of the biological world, cannot yet be described in terms of specific 

 chemical reactions. 



It is surprising, in view of the vast amount of study which has been 

 devoted to the photosynthetic phenomenon, that nothing has been learned 

 concerning what roles the B vitamins may play in this process. It can be 

 anticipated, however, that this question will soon be answered, at least 

 in part, as a result of current investigations which have already yielded 

 much information not previously obtained by the classical methods that 

 have been used in attacking the problem. Two of these recent approachs 

 which are proving to be especially valuable are the study of photosyn- 

 thesis from the standpoint of comparative biochemistry 55 and the cor- 



