ANTIGENS AS BIOCATALYSTS 39 



If a preparation contains an enzyme protein and an inactive protein 

 impurity the immune serum produced against such a mixture will 

 react in the precipitation tests with one or both of them; it will hence 

 be difficult to state whether the precipitinogen was the enzyme or the 

 contaminating protein. We will therefore include only immunological 

 studies carried out using the more highly purified crystalline prep- 

 arations. 



Antibody against Crystalline Urease. Antiurease was the first anti- 

 body produced against a crystalline enzyme, and this is probably 

 the first indubitable proof of the existence of an immune anti-enzyme. 

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

 1937; Howell, 1932) obtained antiurease which behaved like antitox- 

 ins prepared against bacterial toxins in precipitation and neutralization 

 experiments. Antiurease serum inhibited the catalysis of urea into 

 ammonium carbonate by urease, and protected animals against the 

 toxic and fatal effects of ammonia resulting from the dissociation of 

 ammonium carbonate. 



Crystalline urease prepared from jack bean meal of high urease 

 content had an activity of about 135 units per milligram. The crystals 

 under the microscope were seen to be practically uncontaminated by 

 any other material. 



When 1 ml. of crystalline urease solution containing 100 units was 

 injected into the ear vein of rabbits they experienced convulsions in 

 a few minutes and death wdthin an hour. When two rabbits were in- 

 jected intraperitoneally or subcutaneously with 0.5 ml. (50 units) of 

 solution death followed within 48 hours. To prevent the death of 

 rabbits 2.5 to 5 units of urease were injected at the start. The injections 

 were given every eight days for 30 days and then every two or three 

 days for 30 days. The last injections contained 600 units of urease. The 

 serum of rabbits showed the presence of precipitin, though of low titer. 

 However, such a serum was capable of neutralizing the urease, and the 

 urease-antiurease combination was used for immunization against 

 urease. Animals therefore were usually started with a suspension of 

 urease-antiurease in large doses (containing 100 to 1000 urease units, 

 per animal). This indicated that a very effective protective antibody 

 had been produced during the first immunization experiments. During 

 the course of this study it was found that the recrystallized urease of 

 highest purity gave better results than the once-crystallized urease. 



