52 IMM UNO-CATALYSIS 



that "Adult rabbits made hypoproteinemic by a low protein diet or by 

 low-protein diet supplemented by plasmapheresis exhibited a lessened 

 capacity to produce agglutinins as compared with animals of similar 

 age but supplied with an adequate diet," and "Protein repletion of 

 protein-depleted rats by the feeding of high-quality protein, or a 

 hydrolyzate of a high quality protein led to a markedly increased out- 

 put of hemolysin, evident as early as after two days of repletion and 

 pronounced within seven days." The agglutinative titers revealed that 

 the average agglutinin-output of the well-fed rabbits was about five 

 times that of the protein-depleted ones. The serum protein levels of 

 the well-fed group rose to an average of 6.62 grams per 100 ml. 

 whereas those of the low-protein group of rabbits declined to an average 

 level of 4.76. These results show that factors controlling protein 

 metabolism are directly related to the production of antibody. 



According to the studies of Whipple and his collaborators there exists 

 a dynamic equilibrium between the proteins of blood and those of 

 tissues. That is, there is a "give and take" between body and plasma 

 proteins. When plasma protein is depleted, replacement is possible 

 by the proteins of the organs (Madden and Whipple, 1940). The 

 results of the studies of Schoenheimer and his collaborators (1942) 

 with isotopic amino acids have shown that the proteins are in dynamic 

 equilibrium with their constituent fragments. When an isotopic amino 

 acid was added to the diet of a host, the concentration of marked 

 nitrogen in the serum proteins increased immediately, but diminished 

 steadily after the addition of isotopic amino acid to the diet was dis- 

 continued. Chemical reactions had thus occurred among the units 

 of the individual serum proteins, resulting in the uptake of dietary 

 nitrogen in the first period and its removal in the second. The above 

 findings may be presented in the following manner: 



Serum proteins ^ amino acids ^ tissue proteins 



This dynamic equilibrium of protein metabolism, involving pro- 

 teolysis and protein synthesis is mediated by species specific proteinases. 

 From what we know of the species-specificity of proteins and the speci- 

 ficity of enzymes, it would be reasonable to assume that the enzymes 

 of the individuals belonging to the same species metabolize each other's 

 proteins, given parenterally, in an identical manner. Under these con- 



