BIOCHEMICAL REACTIONS AND THEIR CATALYSTS 107 



typical B vitamins appear on this essential list. Cognizance of the relation- 

 ship between each vitamin and a highly specific type reaction enables 

 an investigator to predict which B vitamin, if any, will be involved in 

 a newly discovered enzyme system and which ones would be unlikely to 

 function. Before it was shown that thiamine functioned only in the 

 decarboxylation of ot-keto acids, efforts were often made to demonstrate 

 that thiamine was a component of enzymes which were effective in 

 decarboxylating other types of acids. 



The list of fundamental types of reactions will be incomplete until 

 the biosyntheses of sterols, certain protein constituents, and some other 

 essential compounds have been elucidated. On the basis of the informa- 

 tion now available about the formation and degradation of these com- 

 pounds it seems reasonable to predict that not too many more types of 

 reactions will be found necessary to account for their metabolism. 



Just as it is possible to produce an almost infinite number of proteins 

 from combinations of nineteen or so amino acids, so it should be possible, 

 if the catalysts are available, to produce almost any type of chemical 

 change which a cell requires by the proper combinations of a limited 

 number of relatively simple types of reactions. It may be pointed out 

 here that a limited number of enzymes in the digestive tract are capable 

 of hydrolyzing an inestimable number of different proteins. Could a 

 similar number of enzymes accomplish the reverse synthetic processes? 

 An answer must wait until more knowledge is available concerning the 

 manner in which the amino acids are placed in order during the synthesis 

 of proteins. If the amino acids and intermediate peptides are oriented 

 in some nonenzymatic fashion (by a gene or "organizer"), a small number 

 of specific enzymes could accomplish the syntheses of most simple pro- 

 teins. 



Such speculation concerning the number of types of enzyme reactions 

 offers an independent approach on which to base estimates as to the 

 number of B vitamins yet to be discovered. Undoubtedly several new 

 types of enzymatic reactions occurring generally throughout the biolog- 

 ical realms will be found. Some of these will probably require as co- 

 catalysts specific organic compounds which will be chemically unrelated 

 to any of the known vitamins or other growth-promoting substances. 

 When such substances are found, there will be good reasons for grouping 

 them with the known B vitamins in any classification of biochemical 

 substances based upon functions. 



At one time it seemed necessary to postulate the existence of a large 

 number of types of enzymatic reactions unrelated to those then known 

 in order to account for the catalytic activity of the numerous growth- 

 promoting factors and vitamins which had not yet been associated with 



