ANTI-ENZYME IMMUNITY 331 



of hydrolyzing d-ribonucleic (yeast) acid. It had a molecular weight 

 of about 15,000. Smolens and Sevag (1942) found that this enzyme 

 injected into rabbits intramuscularly and intravenously elicited the 

 formation of specific antibodies. Antibody was produced against crude 

 and five, six and eight times crystahized enzyme preparations. In 

 precipitation tests, immune sera prepared by different routes of in- 

 jection reacted against antigen dilutions up to one million. Ordinarily 

 there persisted a prozone with some antisera as high as to 1:100,000 

 antigen dilution. However, several antisera were prepared which did 

 not show any antigen prozone. 



In control experiments antisera prepared against cattle serum re- 

 acted with cattle serum in dilutions up to 3 1 ,000 without any prozone. 

 Cattle antisera did not react with any of the preparations of ribonu- 

 clease. The cattle serum, likewise, gave no reaction against anti- 

 ribonuclease sera. Normal rabbit sera when tested against the various 

 ribonuclease preparations gave no reaction in any case. 



The amount of the purified enzyme preparation in the antigen-anti- 

 body precipitate was determined by analyzing the precipitates for 

 nitrogen. It was found that the antigen-antibody ratio was about 1 :28 

 (1 : 40,000 antigen dilution). The experiments carried out under these 

 conditions showed that the homologous antibody inhibited the d-ribo- 

 nuclease activity from 10 to 30 per cent. 



2. Neutralization of the Toxic Action of Crystalline 

 Urease by Its Homologous Antibody 



Details of the production and certain properties of immune serum 

 against urease were described in Part I of this treatise. The physio- 

 logical significance of anti-urease immunity will be discussed here 

 further. The fact that urease, like toxins, is extremely poisonous to 

 animal organisms has rendered it, in the hands of Sumner and Kirk, 

 a valuable tool to study various phases of anti-enzyme immune reac- 

 tions. The toxicity is due to the action of urease on the body urea pro- 

 ducing fatal ammonia poisoning. 



Kirk and Sumner (1931, 1934), Sumner and Kirk (1932) and 

 Sumner (1937) showed that as litde as 0.15 mg. (20 units of crys- 

 talline urease) is fatal to a rabbit of 2 kg. body weight. Death occurs 

 when the blood ammonia has reached a concentration of 5 mg./ 100 ml. 



