CATALYSIS AND ENZYME ACTION 71 



some substance which serves as an indicator and thus they 

 appear to be reducing enzymes. 



DEAMIDISING ENZYMES 



The removal of NH 2 groups from amino acids can be 

 brought about by enzymes. The removal of NH 2 groups may 

 be the result of hydrolysis or of oxidation, so we shall not 

 deal with these further as they would come under the hydro- 

 lytic or oxidising enzymes already described. Dakin states 

 that the usual fate of amino acids is that they are oxidised 

 to a-ketonic acids.* 



ANTI-ENZYMES 



These are substances that paralyse the action of enzymes, 

 thus preventing their action. 



COAGULATING ENZYMES 



Coagulation of Milk. Milk when treated with a neutral 

 extract of the stomach of a calf sets to a solid mass which is 

 termed junket. After some hours the junket separates into 

 a liquid called whey, and a solid portion which forms cheese. 



The process that takes place is the conversion of the soluble 

 protein caseinogen into insoluble casein by the action of the 

 enzyme rennin. The casein entangles the fat of the milk 

 so that cheese consists of fat and protein. 



Coagulation of milk requires the presence of calcium salts. 

 If all the calcium is removed from milk by the addition of an 

 oxalate the milk will not clot, but it can be shown that the 

 rennin has acted on the caseinogen by boiling the solution to 

 destroy the rennin, and then adding calcium salts when a 

 precipitate of casein results. The process is said to be that 

 rennin converts caseinogen into casein, and casein forms an 

 insoluble precipitate with calcium. 



Coagulation oj Blood. When blood is shed it becomes 

 viscid, and ultimately sets to a jelly occupying the same 

 volume as the original blood. In the absence of this process of 

 coagulation all surgery would be impossiole, as death from 

 haemorrhage would occur as the result of the slightest wound. 

 This process also requires the presence of calcium salts, as 

 the addition of oxalates to blood prevents its coagulation, 

 however we shall see the relation of calcium to blood coagula- 

 tion is different from its relation to milk coagulation. 



The essential change in blood coagulation is the formation of 

 fibrils of a material termed fibrin. These fibrils form a net- 

 work, which contracts after it is formed. The network, by 



* H. D. Dakin, Oxidations and Reductions in the Animal Body. 

 Longmans, Green & Co., 1912, pp. 52-54. 



