236 ASCORBIC ACID 



aerogenes, Salmonella pullorum, and Salmonella enieritidis were found to be 

 active. Further examination has shown that only Staphylococci and mem- 

 bers of the Enterobacteriaceae'*^ bring al)out the reduction. With intact 

 cells, various substrates may serve as hydrogen donators; these include 

 glucose, lactate, formate, succinate, malate, alcohol, and hydrogen. Cell-free 

 dehydrogenase enzymes prepared from E. coli were ineffective, although 

 such preparations were active in reducing methylene blue. Some other 

 factor^*^ (possibly a carrier) is involved in addition to the dehydrogenases 

 supplying hydrogen. This unknown factor is not identical with or replace- 

 able by methylene blue, pyocyanin, glutathione, coenzyme II, yeast 

 extract, or boiled or unboiled yeast. Besides being able to reduce dehydro- 

 ascorbic acid, the Staphylococci and the Enterobacteriaceae are peculiar in 

 containing cytochrome bi. Spectroscopic observations have indicated that 

 cytochrome bi is oxidized (though incompletely) when dehydroascorbic 

 acid is added. It has been suggested, therefore, that cytochrome bi may be 

 an essential component of the reducing system. 



Although no bacterium not containing cytochrome bi has so far been 

 found which will reduce DHA, some bacteria have been examined which 

 contain cytochrome bi but which will not reduce dehydroascorbic acid. An 

 additional factor besides cytochrome bi appears, therefore, to be involved. 

 This may be a dehydroascorbic acid reductase, since leuco-Nile blue is 

 reoxidized by dehydroascorbic acid more strongly in the presence of cells 

 of a strain which can effect this reduction than with those of a strain which 

 cannot. 



3. Ascorbic Acid and the Metabolism of Tyrosine 



When 0.5 g. or more of L-tyrosine is administered to scorbutic guinea 

 pigs, homogentisic, p-hydroxyphenylpyruvic, and p-hydroxyphenyllactic 

 acids are excreted in the urine. ^''^ These compounds are not formed if the 

 tyrosine is administered with L-ascorbic acid. Similar observations made in 

 infants'"*^ have led to the suggestion that L-ascorbic acid participates di- 

 rectly or indirectly in protein metabolism. 



These results have generally been confirmed by other workers,"* but it 

 has been pointed out that very high doses of L-tyrosine must be consumed 

 by guinea pigs on a scorbutic diet before the failure to rupture the l)enzene 



"1 B. P. Eddy, Biochem. J. (In press.) 



i« B. P. Eddy, M. Ingram, and L. W. Mapson, Proc. Soc. Gen. Microbiol. (1951); 



Biochem. J. (In press.) 

 i« R. R. Sealock and H. E. Silberstein, l^cience 90, 517 (1939); J. Biol. Chem. 135, 



251 (1940). 

 14^ S. Z. Levine, E. Marples, and H. H. Gordon, Science^, 620 (1939); J. Clin. Invest. 



20, 209 (1941). 

 i« H. A. Painter and S. S. Zilva, Biochem. J. 41, 511 (1947). 



