On "Racemized" Casein. 



105 



the tautomeric change suggested by Dakin is not racemization in 

 the ordinary meaning of the term. The discrepancy as to the 

 number of end amino groups in casein, as indicated by the optically 

 active amino acids found by Dakin, is as Kober 1 shows, fatal to 

 Dakin's theory. 



Anticipating the probability that a substance which is so 

 changed as to be unaffected by enzymes and bacteria might also 

 be changed in its antigenic properties, Ten Broeck, 2 at Dakin's 

 suggestion, carried out experiments with "racemized" egg albumin 

 and found that the substance was non-antigenic as shown by the 

 anaphylaxis, precipitin and fixation tests. Underhill and Hen- 

 drix, 3 on the basis of fall of blood pressure and retardation of 

 blood clotting, find that "racemized" casein, egg-albumin and 

 zein are non-toxic, but yield toxic products on partial hydrolysis 

 with acid. The "racemic" proteoses, with the curious exception 

 of zeose, are likewise toxic. It appears, then, that the "racemic" 

 substances are not entirely without action on the body when 

 introduced parenterally. 



The "racemization" of proteins appears to throw some light 

 on the relationship of structure to antigenic property. Based on 

 "racemization" experiments, the work of Dudley and Woodman 4 

 would indicate that casein from the sheep differs from casein 

 obtained from cow's milk. 



In connection with other work being done on the relationship 

 of protein structure and antigenic property, it appeared to the 

 writer of importance to fill in the gap which in the particular 

 case of casein is still missing, and to determine whether racemized 

 casein is likewise non-antigenic. "Racemic" casein was prepared 

 essentially according to Dakin's method, except that for the 

 purpose of drying the product readily, it was washed with alcohol 

 and ether which removed the larger portion of the caseose with 

 which it is usually contaminated. In preparing solutions of both 

 casein and the racemized product, sufficient alkali was added to 

 make the solution neutral to litmus. The rabbits received injec- 



1 Kober, P. A., J. Biol. Chem., 1915, 22, 433. 



2 Ten Broeck, C, J. Biol. Chem., 1914, 17, 369. 



'Underhill, F. P. and Hendrix, B. M., J. Biol. Chem., 1915, 22, 453. 

 4 Dudley, H. W. and Woodman, H. E., Biochem. J., 1915, 9. 97. 



