216 



ASCORBIC ACID 



other produce L-ascorbic acid when fed to cress seedhngs or injected into 

 rats. The evidence from this work indicates that L-ascorbic acid may be 

 formed by a sequence of reactions as follows. 



H OH 



\ / 

 C 



2 HCOH 



I 



3 HOCH 



I 



4 HCOH 



5 HC 



6 



CHjOH 



D-Glucose 



H OH 



\ / 



C — 

 I 

 HCOH 



Fh 



HCOH 

 O 1 

 |HC- 



■—CO 







] 



CO 



I 



— CH 



I < 

 HOCH 



O HC — 



HOCH 



I 



-A 



HO H 



Alternative forms of writing 



D-glucurono--)-Iactone to show 



inversion of configuration 



CO -I 



I 

 HOCH 



I 

 HOCH 



I 

 HC 



I 

 HOCH 



O 



"J 



CHoOH 



L-Gulono- 

 7-lactonc 



con 



I 



HOC 



II o 



HOC 



I 

 HC 



I 

 HOCH 



J 



CHsOH 



L- Ascorbic 

 acid 



V^ 



HCOH 

 I 

 HOCH o 

 I ^ 

 HOCH 

 I 

 HC — 



CH2OH 

 D-Galactose 



H OH 



V- 



I 



HCOH 



I 

 HOCH o 



I 

 HOCH 



COOH 



I 

 CH 



I 

 HCOH 



I 

 HCOH 



I 

 HOCH 



I 



-A 



H OH 



Alternative forms of writing 



D-galacturonic acid to show 



inversion of configuration 



HC — 

 I 

 COOH 



CO- 



I 

 HOCH 



I 

 HCOH 



I 

 HC 



HOCH 

 I 

 CH2OH 



L-Galactono- 

 7-lactone 



CO— 1 



I 



O 



HOC 



II 

 HOC 



1 I 

 HC 1 



I 

 HOCH 



I 



CHoOH 



L- Ascorbic 

 acid 



A fundamental feature of both reaction chains is the change from the 

 D to the L series with inversion of the whole molecule at the second step; 

 which of these reaction sequences is the more important in the synthesis of 

 L-ascorbic acid in the plant or animal is not at present known. 



Confirmation that the synthesis of ascorbic acid in vivo does in fact 

 proceed along these or very similar pathways has been forthcoming by 

 recent observations^-^ that both D-galacturonic acid methyl ester and 

 L-galactono-7-lactone are converted in vitro to L-ascorbic acid by extracts 

 from plant tissues. The oxidation of L-galactono-7-lactoiie to L-ascorbic acid 

 was found to be catalyzed by the cytoplasmic particles (mitochondria) of the 

 cell prepared from germinating pea seeds. The o))servations also showed 



32b L. W. Mapson, F. A. Isherwood, and Y.-T. Chen, Biochem. J. (1953, in press). 



