IV. BIOCHEMICAL SYSTEMS 237 



ring in a part of the ingested compound can be observed. Secondly, this 

 l)iochemical abnormality becomes effective very soon after the L-ascorbic 

 acid has been removed from the diet, the maximum excretion of hydroxy- 

 phenyl compoiuids occurring as early as 24 to 48 hours after the animals 

 were depri\'ed of the \'itamin. In other words this abnormality appears 

 even when the tissues of the guinea pig are still saturated with L-ascorliic 

 acid. The phenomenon is also seen in animals which are capable of synthe- 

 sizing their own ascorbic acid if high doses of tyrosine are given. •''^ Abnor- 

 mal excretion of intermediate products may therefore occur even in the 

 normal animal. The necessity for the presence of an excess of L-ascorbic 

 acid in order that all the tyrosine shall be completely metabolized is no 

 indication of the existence of a connection between the normal function of 

 L-ascorbic acid and the metabolism of aromatic or of other amino acids. 

 The apparent interaction in vivo between L-ascorbic acid and L-tyrosine 

 suggests rather a physiological response to an unusual situation. Subse- 

 quent work has shown that the production of hydroxyphenyl compounds 

 from tyrosine may occur in the intestinal tract of scorbutic guinea pigs 

 and that the accumulation of these compounds is inhibited by the presence 

 of L-ascorbic acid.^" If bactericidal agents are fed in combination with 

 L-ascorbic acid, there is an accumulation of hydroxyphenyl compounds in 

 the intestine. The suggestion is made that L-tyrosine is normally quickly 

 destroj^ed by microorganisms and that the rate of the destruction can be 

 slowed down either l)y administering l)actericidal agents or by withholding 

 L-ascorbic acid. The presence of L-ascorbic acid may favor those micro- 

 organisms capable of attacking phenolic groups. The \'itamin may even 

 act in the chain of reactions concerned in the degradation both in l^acterial 

 and animal cells. This appears probable from w^ork on liver slices from 

 normal and scorbutic guinea pigs.'"** The oxygen uptake of liver slices from 

 normal animals is increased on the addition of tyrosine in an amount 

 equi\"alent to one atom of oxygen per mole of tyrosine. This increased 

 oxygen uptake was not observed, however, in liver slices from scorbutic 

 animals, unless ascorbic acid was also added. The fact that both tyrosine 

 and phenylalanine are converted to the aromatic keto acids, even in the 

 scorbutic animal, suggests that oxidative deamination proceeds in the ab- 

 sence of ascorbic acid, but that the further oxidation of the aromatic keto 

 acids is dependent on the presence of ascorbic acid. D-Glucoascorbic acid, 

 which is })iologically inactive, also accelerates these reactions to the same 



'""^ Y. Kotake, G. Matsuoka, and I\I. O. Kagawa, Hoppe-Seyler's Z. physwl. Chem. 



122, ICG (1922). 

 '" H. A. Painter and S. S. Zilva, Biochem. J. 43, 398 (1948). 

 '« T. H. Lan and R. R. Sealock, J. Biol. Chem. 155, 483 (1945); R. R. Sealock and 



T. H. Lan, J. Biol. Chem. 167, 689 (1947). 



