MECHANISM OF PROTEIN HYDROLYSIS AND IMMUNIZATION 41 



The second laboratory investigation, to which reference was 

 just made, concerns the presence of uric acid in the red cor- 

 puscles. In the Journal of Biological Chemistry, August 20, 

 1915, Benedict shows that uric acid exists in the blood in two 

 forms, in a "free" and in a "combined." Ox-blood, which, when 

 tested by the method of Folin, hitherto considered reliable, 

 showed a content of 0.2 mgm. of uric acid per 100 c.mm., was 

 found as a rule to contain in reality about 7 mgm. of total 

 uric acid per 100 c.c. of blood, practically all of this being con- 

 tained in the red blood cells. "If the ox blood were allowed to 

 stand at room temperature and protected from bacterial con- 

 tamination, there was found to take place a gradual transition 

 from the combination to the free form of uric acid, apparently 

 due to the action of some ferment. . . . Benedict suggests that 

 possibly the free uric acid is that which is ready for excretion as 

 such, while the combined is capable of further catabolism." 

 (Summary appearing in Medical Record.} 



It must be obvious that this finding of large quantities of uric 

 acid in the red cells gives strong support to that part of the pro- 

 teomorphic theory which postulates the red cells as the seat of 

 the enzymic activities which accomplish the ultimate decompound- 

 ing of the protein by-products. Uric acid is one of the most im- 

 portant of these by-products. It chances to be one that can ulti- 

 mately be eliminated by way of the kidneys ; but whether the red 

 cells excrete it into the blood for that purpose, or whether it 

 merely is left in the blood stream when the red cell is disin- 

 tegrated in the liver, is still conjectural. Meantime Benedict's 

 experiments give additional evidence that the red cells have pre- 

 cisely such enzymic functions in connection with the later stages 

 of decompounding of the protein molecule as the proteomorphic 

 theory postulates. 



Possibly a few words of further exposition and interpretation 

 may be desirable, illustrating a little more in detail the chemical 

 aspects of the observed facts in connection with the suggested 

 explanation along the lines of the proteomorphic theory. 



Note, then, that the chemical formula of uric acid is C 5 H 4 N 4 O 3 . 

 Obviously we have here a substance not distantly related to some 

 of the amino-acids, but proportionally richer in nitrogen than 

 any one of these, the only one approaching it in this regard 

 being arginine (C 6 H 14 N 4 O 2 ). Another significant distinction be- 

 tween uric acid and amino-acids is the fact that it contains three 

 atoms of oxygen and only four atoms of hydrogen. There is 

 no amino-acid with less than five atoms of hydrogen; and all 

 but three of them have either two or four atoms of oxygen, each 

 of the three exceptional ones having only a single atom of 

 nitrogen. 



