BIOCHEMICAL REACTIONS AND THEIR CATALYSTS 



105 



IV. Simple oxidations and reductions in Nicotinic acid 



which the following types of double Riboflavin 



bonds are created or reduced by the Porphyrins* 



removal or addition of hydrogen 

 atoms (or the addition or loss of elec- 

 trons) . 



A. C=0 



C=C 



B. C=N- 



D. 0=0 



Thiamine 

 (Biotin?) 

 Pyridoxal 



V. Decarboxylations of keto acids and the 

 reverse reactions. 



A. a-Keto acid decarboxylations 



B. /?-Keto acid decarboxylations 

 VI. Reactions of amino acids requiring 



activation of the a-position. 



A. Transaminations 



B. a-Amino acid decarboxylations 

 VII. Condensations and cleavages creating 



or rupturing carbon-to-carbon bonds, 

 (other than carboxylations) . 



A. Aldol type 



B. Reactions in which acetyl deriva- 

 tives are condensed or formed 



C. Reactions in which "activated single 

 carbon unit participates! 

 cleavedf 



VIII. Other reactions in which the single 

 carbon unit participates! 

 To place vitamin Bi 2 in the classification now would be premature, 

 since concentrates known to be free from other biological agents have 

 been available for only a few months. It is possible, however, to indicate 

 that vitamin Bi 2 functions (perhaps indirectly) in the group of reactions 

 for which p-aminobenzoic acid or folic acid are essential. 



* The reasons for including porphyrins with the B vitamins in this discussion will 

 be taken up later (p. 151). 



t This group of reactions is not yet as completely characterized as are the other 

 types. There is some question concerning the exact compounds which enter into the 

 reactions and the information on the component parts of the enzymes is still incom- 

 plete. However, these types of reactions have been included because of the abun- 

 dance of circumstantial evidence concerning them (see p. 198). 



none 

 Pantothenic acid 



p-Aminobenzoic acid 

 Folic acid 



p-Aminobenzoic acid 

 Folic acid 



