42 IMMUNO-CATALYSIS 



sufficiently clear cut to show that all four of these enzymes and their 

 precursors can be differentiated by this reaction." 



Antibody against Pefsin and Vefsinogen. Seastone and Herriott 

 (1937) carried out experiments to distinguish by serological methods 

 the pepsins from several different animal species as well as to compare 

 the serological behavior of pepsin and its precursor, pepsinogen. 

 Northrop had previously reported (1930) that crystalline swine pepsin 

 protein gave rise to pepsin precipitating antibodies. Seastone and 

 Herriott were aware of the fact commented on by other investigators, 

 that pepsin is inactivated above pH 6; as a more alkaline condition is 

 approached the enzyme is converted into a typical denatured protein. 

 At normal body temperature and at blood pH 7.6 it is therefore most 

 likely that active pepsin in the body fluids is inactive, and denatured 

 pepsin is responsible for antibodies developed following the injection 

 of active pepsin. The limitations imposed by its denaturation at pH 

 7.6 must be accepted. 



Immunization. Rabbits weighing about 2 kg. were given, at weekly 

 intervals, three intraperitoneal injections of 5.0 ml. of a 1 per cent 

 solution of swine pepsin at pH 5.0. This material had been twice 

 crystallized and dialyzed. Two weeks after the last injection, the 

 serum was collected. Precipitin reactions were done by the ring test, 

 and readings were made after \Vi hours at room temperature. Of four 

 rabbit sera, two showed no pepsin precipitins; one precipitated pepsin 

 solution (pH 7.6) at a concentration of 1:1000 and 1:100,000. Anti- 

 sera against swine serum were also prepared, the strongest reacting 

 wdth normal swine sera in dilutions (on the basis of dry weight) of 

 1:100,000. Pepsinogen gave rise to precipitating antibodies more 

 readily than pepsin. At pH 7.6 it is a stable native protein. Of the 

 four rabbits immunized with pepsinogen, two had a titer of 1 : 100,000 

 and two 1:1,000,000. 



Their findings further showed that alkali (pH 7.6) denatured pep- 

 sins from swine, cattle, and guinea pigs precipitated in swine pepsin 

 antiserum; pepsin from the rabbit, chicken, and shark treated simi- 

 larly did not precipitate in swine pepsin antiserum. Pepsin antisera 

 reacted with both pepsin and pepsinogen but did not react with the 

 serum proteins from the homologous species. Anti-sera made with 

 serum proteins did not react with the homologous pepsin or pepsino- 

 gen. Pepsinogen anti-sera reacted with pepsinogen, but not with 



