ANTIBODIES AGAINST RESPIRATORY ENZYMES 385 



source of mammalian hexokinase when substituted for yeast hexokinase 

 was not inhibited by rabbit normal and antiyeast hexokinase sera. 

 Three-tenths ml. of brain extract was approximately equivalent in 

 activity to 0.1 ml. of our yeast hexokinase preparation. 



Four-tenths ml. of immune serum completely inhibits the activity of 

 0.1 ml. of hexokinase (0.1 mg. protein) solution. The inhibitions by 

 0.05 ml., 0.1 ml. and 0.2 ml. of immune serum are respectively, 42%, 

 73% and 94% (Fig. 1). The data presented in Fig. 2 show similar 

 qualitative relationship with respect to the inhibition with various 

 volumes of immune serum. The optimal volume (0.4 ml.) of immune 

 serum added at a time when hexokinase activity was at its peak 

 brought about an immediate inhibitory effect which persisted through 

 the two hour period. This relationship between an enzyme and its 

 homologous antibody would appear to be analogous to the inhibition of 

 enzymes with specific inhibitors. 



According to our unpublished data immune serum prepared against 

 the whole yeast cell was found to produce 79% inhibition of the 

 activity of dialyzed hexokinase preparation. Due to technical dif- 

 ficulties, the effect of the immune serum prepared against the isolated 

 hexokinase on the hexokinase activity of the whole yeast cell has not 

 as yet been determined. 



4. Inhibition of Yeast d-Glyceraldehyde-3-phosphate 

 Dehydrogenase by Specific Anti-Serum 



Krebs and Najjar (1948) produced specific antibody in rabbits to the 

 yeast dehydrogenase involved in the reversible oxidation of d-glyceral- 

 dehyde-3-phosphate : 



d-Glyceraldehyde-3-phosphate+H3P04+DPN^ 



1,3-diphosphoglyceric acid-[-DPNH2 



For immunization of the rabbits, the electrophoretically nearly 

 homogeneous crystalline enzyme was used, but some of the animals 

 received injections of the enzyme solution immediately before crystal- 

 lization. The enzyme preparation contained DPN apparently bound to 

 protein (cf. Taylor, Velick, Cori, Cori and Slein, 1948). Cysteine was 

 necessary to obtain maximum activity. 



Four medium sized rabbits were given a series of five subcutaneous 



