334 IMMUNO-CATALYSIS 



penicillinase by injections on alternate days for five weeks. Precipitin 

 reactions occurred in immune serum dilutions through 1 : 56. Inhibition 

 tests were performed either by holding the penicillinase concentration 

 constant and diluting the sera, or by keeping the concentration of sera 

 constant and diluting the penicillinase. The enzymatic action of peni- 

 cillinase was lost completely after contact for one hour at 37° C. with 

 immune serum dilutions as high as 1 : 1 12. A partial loss was observed 

 with serum dilutions of 1 : 224, 1 : 448 and 1 : 896. There was no 

 observable inhibition with normal rabbit serum. There was no loss in 

 enzyme activity when the enzyme, horse serum, rabbit antihorse serum, 

 and saline were mixed and allowed to stand for one hour at 37° C. In 

 manometric measurements, it was found that penicillinase incubated 

 at 37° C. for one hour with antipenicillinase lost about 90 per cent of 

 its activity. Antipenicillinase was found to combine with the enzyme 

 almost immediately when it was introduced after allowing the peni- 

 cillin-penicillinase reaction to proceed for 15 minutes. Controls indi- 

 cated that there was no CO2 retention by the concentration of serum 

 used. 



The data presented by Housewright and Henry (1947b) show that 

 the substrate and the inhibiting antibody compete for the active site 

 of penicillinase. When penicillinase and antipenicillinase react first, 

 penicillin is incapable of counteracting or displacing the antibody from 

 its combination with the enzyme; under this condition the inhibition 

 of the enzyme is about 93 per cent. On the other hand, when the anti- 

 body was added to the enzyme-substrate reaction system, it was able 

 to displace the substrate partially from the active site of the enzyme. 

 Under these conditions, the inhibition at the end of 110 minutes was 

 about 59 per cent. At this period, the curve indicated flattening and 

 therefore two states of equilibrium. 



Penicillinase -f- Penicillin-]- Antipenicillinase 



Penicillinase — Penicillin Penicillinase — Antipenicillinase 



Penicilloic acid-|-Penicillinase 



