382 IMMUNO-CATALYSIS 



to the reaction mixture. Final total volume=:13.0 ml.; pH=7.45; the 

 depth of the reaction solution— 2.93 cm. 



The results of measurements were as follows: (a) normal rabbit 

 plasma did not inhibit the activity of the enzyme, (b) immune plasma 

 exercised inhibition, and (c) immune plasma against rat tumor enzyme 

 protein and that against rat muscle enzyme protein exercised iden- 

 tical inhibitions against one or the other enzyme proteins. 



The degrees of inhibition were dependent on the concentration of 

 pyruvate. In the presence of 1X10~^ M pyruvate the inhibition was 

 75 per cent. Increasing the concentration to 20X 10~^ M the inhibition 

 was reduced to 45 per cent. This observation has experimental as 

 well as theoretical significance. It would appear that the anti-reductase 

 competes with the substrate pyruvate (possibly also with the dihydro- 

 coenzyme I) for the same active group of the enzyme protein (or 

 the combining site of the antigen). The results would indicate that 

 antibody displaces pyruvate (possibly also the coenzyme) from its 

 combination with the enzyme. However, another possible explana- 

 tion of the above inhibition would be that the combination of the 

 enzyme with the antibody occurs at sites other than that involved 

 in the enzyme-substrate reaction. This combination may offer steric 

 hindrance to the free access of substrate to the site of enzyme activity, 

 or merely reduce the affinity of the enzyme complex for its specific 

 substrate. 



3. Inhibition of Yeast Hexokinase by Homologous 

 Antiserum 



As a continuation of the studies reported by Sevag and Miller 

 (1948), Miller, Pasternak and Sevag (1949) investigated the effect of 

 homologous rabbit immune serum on the activity of hexokinase isolated 

 from yeast. 



It is known (von Euler and Adler, 1935; Meyerhof, 1935; Colowick 

 and Kalckar, 1943) that hexokinase catalyzes the transfer of one 

 phosphate group from adenosine-triphosphate to glucose with the 

 formation of glucose-6-phosphate. In this reaction an alcohol hydroxylic 

 hydrogen is converted to a more acidic hydrogen. 



The effect of anti-hexokinase rabbit serum on the formation of the 

 acidic hydrogen in this system was determined. As will be seen below, 



