PLANT METABOLISM 



219 



CH9OH 



0. H 



CH2OH 



HO/H 



OPOj 



H HO 



ghicosc-l -phosphate 



galactose uridyl 

 transferase 



CH2OH 



uridine diphosphogalactose 



O, H 



CHgOH 



OH 



O^ H 



0P0o= 



H OH 



galactose-l-phosphate 



O O 



O — P— 0— P— O— CH2 /O 



o 



.0 



N 



o 



uridine diphosphoglucose 



galactose-1 -phosphate appears as long as the equilibrium conditions 

 are not satisfied. 



The biological synthesis of L-ascorbic acid (vitamin C) may be 

 taken as an example of the formation of special materials from hexoses. 

 Studies with peas and mung beans indicate that this acid may be 

 derived as follows, where UDP represents the uridine diphosphate 

 portion of the molecule: 



CH2OH 



COOH 



0. H 



UDP 



-O. H 



uridine diphospho- 

 galactose 



OH H, 

 H N— K UDP 



uridine diphospho- 

 galacturonic acid 



H 



HO Jr -0=0 



— C— H 



H 



H 



OH 



UDP 



uridine diphospho- 

 galacturonolactone 



TPNH 



HO 



,0=0 



C=0 



CH2OH 



+ UDP 



CH2OH 



H OH 



L-ascorbic acid 



H OH 

 galactu ronolactone 



