IV. niOCIIKMICAL SYSTIOMS 231 



rosiiK was ohlaiiunl if methylene blue replaced ascorbic; acid. It wa.s further 

 found that in sucii a system, when the ascorbic acid was being oxidized, a 

 pij;nicnt was formed in sohition; tiu> more rai)id the rate of oxidation, tlu^ 

 more ra|)id the formation of the pigment. This pigment was formed only 

 when ascorbic acid was being oxidized and could not be produced in the 

 absence of ascorbic acid by other oxidants such as oxygen or IbjOo. On the 

 a\'ailable evidence, the suggestion was made that the pigment exists in a 

 colored oxidized state and a colorless reduced state, and that the leuco 

 piguKMit leacts only with dehydroascorbic acid as follows: 



Leuco pigment + dehydroascorbic acid = Pigment + ascorbic c-icid 



Since both oxj'gen and ascorbic acid were found to be necessary for the 

 development of the pigment, it was concluded that dehydroascorbic acid 

 was directly responsible and, moreover, that the pigment as a carrier of 

 hydrogen must be positioned between coenzyme I and ascorbic acid for, 

 if it were a terminal carrier, oxygen and not dehydroascorbic acid would be 

 required for its development. 



The nature of this pigment was not identified, but the suggestion was 

 made that it might be identical with or similar to either Palladine's re- 

 spiratory chromogens,"^ Robinson's leucoanthocyanins,'^^ the respiratory 

 pigment Hermidin extracted from Mercurialis,^^^ Szent-Gyorgyi's vitamin 

 pijo fyy ^jjg oxidative-reduction enzyme reported by Wawra and Webb.'-' 

 On the basis of their work, the author has proposed the following scheme 

 for the system: 



Malate malic dehydrogenase_^ Coenzyme I -^ Flavin Ha -^ Leuco pigment -* 



w jr. jr 



Coenzyme I II2 Flavin Pigment 



DHA O2 



AA Ascorbic oxidase 



Further evidence of a link between coenzyme I and ascorbic acid has 

 recently been reported.'-- An enzyme preparation has been obtained from 

 green peas which catalyzes the oxidation of reduced coenzyme I by oxygen 

 in the presence of either methylene blue or ascorbic acid. This reaction was 

 found to be insensitive to cyanide. The enzyme preparation catalyzed the 

 oxidation of reduced coenzyme II with methylene blue but not with ascor- 



»'' W. Palladin, Biochem. Z. 27, 442 (1910). 



"' G. M. Robinson and li. Robinson, ./. Chcm. Soc. 1935, 744. 



"9 P. Haas and T. G. Hill, Ann. But. 39, 861 (1925). 



'=" A. Bentsath, St. Rusznak, and A. Szent-Gyorgyi, Nature 139, 326 (1937). 



'21 C. Z. Wawra and J. L. Webb, Science 96, 302 (1942). 



'" B. Matthews, J. Biol. Chem. 189, 695 (1951). 



