IV 



VITAMIN BIOSYNTHESIS 



IIQ 





;cH 



=N 



o 



CH, 



H OH H II 



HC— C — C— C — CHj-O— P— O— P— O— CHo-CH— CH— C— NH-CHo-CHo-C— NH— CH2 

 H II II I 



OH OH CH3 OH CHj, 



I 

 SH 



O —I 



OPO,H 



3 "^2 



Fig. 57. Coenzyme A. 



10. p-Aminobenzoic acid and folic acid compounds 



Folic acid compounds function in "one carbon compound" transfer reactions 

 leading to the synthesis of the methyl group of thymine, the ^-carbon of serine, 

 carbons 2 and 8 of the purines and other building blocks of protoplasm. All forms 

 of folic acid contain a /j-aminobenzoic acid (PABA) residue. The structural for- 

 mulas of PABA, folic acid, and certain related compounds are shown in Fig. 58. 



It is probable that N^'^-formyl tetrahydrofolic acid (N^O-formyl-THFA) and 

 Nio-hydroxymethyltetrahydrofolic acid (N10-HOCH2-THFA) or closely related 

 derivatives are the actual coenzyme forms of folic acid in the cell. The postulated 

 relationship between some of the above compounds is shown in Fig. 59. 



Shikimic acid is a precursor of PABA. Certain E. coli and Aerobacter aerogenes 



H,N VCOOH HOGG 



PABA Rhizopterin 



Folic 



OH 



NHs 



N - Formyl -tetra-hydrofolic 

 Fig. 58. Structure of folic acid and related compounds. 



Literature p. 124 



