244 B. CINADER AND J. H. PEARCE [13 



with Freund's adjuvant followed by several courses of intravenous injections. 

 The combining ratios of antibody and antigen were obtained directly in 

 excess antibody (Table 1) and indirectly in excess antigen (Table 2), using 

 a procedure described by Heidelberger and Kendall (1935); see also Kabat 

 and Mayer (1948). 



ANTIBODY AS ENZYME-INHIBITOR 

 (see also Cinader, 1957) 



The enzyme action of ribonuclease is inhibited by antibody. This is best 

 shown by adding increasing amounts of the antibody to a constant amount 

 of enzyme (Cinader, 1953, 1955). A plot of enzyme activity, as a function 

 of the quantity of antibody added, shows initially a linear decrease and 

 finally levels out in excess antibody at a fairly constant residual activity. 

 This final constant level of activity is not the same for every serum and 

 varies during the course of immunization. Initially only 60-70% of the en- 

 zyme activity may be inhibited by excess antibody, but antibody formed 

 after repeated courses of immunization inhibits 95-98% of the activity of 

 the enzyme. The changes in inhibitory power of a series of bleedings from 

 a rabbit are shown in Fig. 3. The rabbit was first injected subcutaneously 

 with Freund's adjuvant and received later successive courses of intravenous 

 injections. The marked change of inhibitory power is not due to a decrease 



LOG,o(VOL. SERUM xlO^) 



Fig. 3. Changes in inhibiting potency of antibody produced in response to repeated 

 courses of immunization. 



The effect of the addition of increasing volumes of immune serum to constant quantities 

 of bovine ribonuclease. 



Ribonuclease antisera from rabbit 619 

 Symbol Date of bleeding 



— O— 10.7.54 



— X — 2.8.54 



— i— 22.9.54 



-/\- 1.6.55 



