ANTIBODY AS A SPECIFIC ENZYME INHIBITOR 163 



trypsin inhibitor is a polypeptide with a molecular weight of 6000. It is 

 likewise not precipitable with 2.5 per cent trichloracetic acid, either 

 hot or cold, nor by boiling in water. A solution of the inhibitor mixed 

 with a solution of trypsin of equal molecular strength at pH 7.0 in 30 

 minutes at 6°C. completely inactivates trypsin. The inhibitor forms a 

 compound with trypsin which is dissociable at pH 1 .0. The inactivating 

 effect of the inhibitor is demonstrated in experiments on the digestion 

 of casein, the digestion of sturin, or the activation of chymotrypsinogen 

 into chymotrypsin, or trypsinogen into trypsin in the presence of 

 trypsin or salt, and the clotting of blood. The substance also inhibits 

 chymotrypsin but to a less marked extent. One molecule of inhibitor 

 combining with one molecule of trypsin results in the formation of 

 inhibitor-trypsin complex in the form of hexagonal, many-faced crystals 

 with a molecular weight of 40,000. This combination is split by 

 trichloracetic acid which precipitates trypsin and leaves the inhibitor in 

 solution. 



3. Trypsin Inhibitor of Blood Serum 



It is known that normal serum also contains trypsin inhibitor which 

 blocks the activity of trypsin. Schmitz (1938) isolated this inhibitor in 

 various ways. On precipitating the serum proteins with trichloracetic 

 acid the inhibitor remained in the supernatant acid solution. It was 

 separated by ultrafiltration from the proteins. After precipitation of 

 serum proteins with acetone the inhibitor was found in the acetone 

 solution. The behavior of this inhibitor against trypsin was analogous 

 to the inhibitor isolated from pancreas by Kunitz and Northrop 

 (1936). 



4. Inhibition of Carbohydrases by the Reaction Products 



A disaccharide or glucoside such as sucrose, with specific affinity 

 for invertase, on hydrolysis yields reaction products which manifest 

 inhibitory affinities for the enzyme. Thus fructose and glucose, the 

 products of hydrolysis, inhibit invertase markedly (Henri, 1902; 

 Michaelis and Menten, 1913). a-Methylglucoside which has the same 

 configuration as the a-glucose is also found to inhibit invertase 

 (Michaelis and Rona, 1914). On the other hand, those disaccharides 

 and glucosides, such as maltose, lactose and /?-methylglucoside, possess- 



