D. E. GREEN 



and the rates at which they are synthesized, we would have all the 

 necessary data for determining the flavin requirements of that organ- 

 ism. There are much easier methods of getting at that data at the mo- 

 ment, but it is of considerable theoretical interest to arrive at the data 

 from the enzyme side. 



There are some well-informed workers in the field of nutrition 

 who are unwilling to concede that all vitamins must have a catalytic 

 function. While they admit that the relationship has been established 

 in at least four and possibly six instances, they do not regard these 

 necessarily as precedents. In 1941 the enzyme-trace substance 

 theory (3) was developed which predicted that any substance necessary 

 in the diet in trace amounts must be an essential part of some enzyme 

 system. The theory was not meant to imply that substances required 

 in higher concentrations cannot be essential parts of enzymes. That 

 may or may not be the case. However, amounts of the order of 10 

 fjLg. per kg. per day were regarded as conclusive evidence of a catalytic 

 role for that substance. On the basis of the enzyme-trace substance 

 theory we may confidently expect in the near future the identification 

 of biotin, pantothenic acid, folic acid, vitamin A, vitamin K, and vita- 

 min D with essential parts of new prosthetic groups. The daily re- 

 quirements of vitamin C are about a thousand times greater than 

 those for most of the other vitamins, and, certainly, are well beyond 

 the trace level. The possibility is therefore open that vitamin C may 

 have no catalytic function whatsoever. The recent investigations of 

 Sealock on the role of vitamin G in the oxidation of tyrosine in the liver 

 however, do not encourage the view that vitamin G is an exception 

 to the vitamin-enzyme relation. 



In recent years the exact nutritional requirements of many 

 bacteria and molds have been carefully investigated. A study of any 

 of the synthetic diets proves very instructive from the standpoint of 

 enzyme chemistry. The list of required substances can be easily 

 divided into two categories: (7) substrates of enzyme systems, e. g., 

 amino acids, glutamine, dextrose, fatty acids, purines, etc.; and (2) 

 precursors of prosthetic groups, e. g., vitamins such as riboflavin, 

 thiamin, etc. or the building stones thereof, hemin, and trace metals. 

 The members of the first category can be classified not only on the basis 

 of what we know about their intermediary metabolism but also on 

 the basis of the amounts required, which are vastly in excess of the 



