234 ASCORBIC ACID 



This suggestion was criticized by Barron'^^ on the grounds that there is 

 very little GSH in plants and a large amount of ascorbic acid. The answer to 

 this is that the concentrations of both GSH and ascorbic acid used in Hop- 

 kin's experiments were well within the physiological ranges known to occur 

 in plants, and neither were the ratios of GSH and ascorbic acid unphysio- 

 logical, since GSH and ascorbic acid occur in a molar ratio of 2:1 in one 

 plant at least (potato tubers). 



Evidence has been accumulating that both plant and animal tissues 

 possess the power to reduce — S — S — ■ compounds to SH compounds. In 

 germinating seeds sulfhydryl groups appear rapidly after hydration of the 

 seeds/^- and the sulfhydryl compounds produced have been shown to be 

 mainly glutathione.'^^ Oxidized glutathione, when added to powdered pea 

 seeds, was rapidly converted to the reduced form. With animal tissues 

 GSSG may be reduced to GSH in the presence of glucose dehydrogenase 

 and an activator prepared from liver tissue. With extracts of blood and 

 yeast, GSSG was reduced in the presence of hexose monophosphate and 

 extracts containing coenzyme II. '^^ 



Bukin'^* related the glutathione-ascorbic acid systems to coenzyme I on 

 the evidence that oxidized glutathione may be reduced by dihydrocoenzyme 

 I in a simple non-enzymic reaction. The rate of enzymic oxidation of gluta- 

 thione has also been found to be increased by the presence of coenzyme I 

 in kidney homogenates, and these reactions are stimulated by the presence 

 of ascorbic acid both in the presence and absence of cytochrome c."^ 



The claim that dihydrocoenzyme I will reduce oxidized glutathione has 

 not, however, been substantiated by other workers, either as a non-enzymic 

 reaction or by systems containing dehydrogenase enzymes and substrates 

 with added coenzyme I and oxidized glutathione.'^^' '^^ It seems probable 

 that earlier workers may have had coenzyme II as an impurity in their 

 coenzyme I preparations. Until recently, however, the evidence for the 

 cooperation of glutathione with coenzyme-linked reducing systems has been 

 contradictory and based in plants on the premise of a non-enzymic reaction. 

 Recent work,'^^ ■ '^^ however, has demonstrated the existence in many plant 



"1 E. S. G. Barron, Cold Spring Harbor Symposia Quant. Biol. 7, 145 (1939). 



132 M. J. Firket and M. Comhaire, Bidl. acad. roy. med. Belg. 9, 93 (1929); R. Vivario 



and J. LeClaux, Arch. Intern. Physiol. 32, 1 (1930). 

 "3 F. G. Hopkins and E. J. Morgan, Nature 152, 288 (1943). 

 13* P. J. G. Mann, Biochem. J. 26, 785 (1932). 

 "6 V. N. Bukin, Biokhimiya 18, 60 (1943). 

 "6 E. Stotz, C. J. Harrer, M. O. Schultze, and C. G. King, J. Biol. Chem. 122, 407 



(1938). 

 1" L. W. Mapson and D. R. Goddard, Nature 167, 975 (1951) ; L. W. Mapson and D. R. 



Goddard, Biochem. J. (In press.) 

 "8 E. E. Conn and B. Vennesland, Nature 167, 976 (1951). 



