30 CHEMICAL STATICS 



9. "Racemized" Proteins. — It has recently been shown by 

 Kossel (36) and by Dakin (11) (12) that treatment of proteins 

 with rather concentrated alkah leads to a progressive diminu- 

 tion of the optical rotary power of the solutions. This Dakin 

 attributes to an internal racemization or, more correctly, enoli- 

 zation of the protein molecule analogous to that which occurs in 

 the hydantoins (10). He depicts the reaction as follows: 



NH-CO- 

 1 

 R-CH-CO-NH-CHR-COOH 



NH-CO- 

 I 

 <=>R-C = C(OH)-NH-CHR-COOH 



the alkali tending to shift the equilibrium towards the right. 

 The central carbon atom instead of being attached by its valencies 

 to four different groups is now attached to three groups, to one 

 of them by a double bond, and any optical activity which it may 

 have possessed owing to assymetry must have been lost. 



The "racemized" proteins thus prepared are totally resistant 

 to hydrolysis by pepsin, trypsin or erepsin. Putrefactive bac- 

 teria do not attack "racemized" casein although they slowly 

 decompose the "racemized" caseose (proteose) which is simul- 

 taneously formed through partial hydrolysis of the casein and 

 subsequent "racemization" of the higher products of the hydroly- 

 sis. "Racemized" egg albumin (7) and casein (63) are non- 

 antigenic. The amino-acids resulting from the complete hy- 

 drolysis of "racemized" protein by acid are for the most part 

 optically inactive (12). 



A number of objections have been urged by Kober (32) against 

 Dakin's interpretation of the progressive loss of optical activity 

 of proteins in alkaline solutions. In the first place he points 

 out that the presence of an oscillating hydrogen atom within 

 the molecule might be anticipated to lead to the development of 

 bands in the absorption spectrum and no absorption-bands are 

 observable in protein solutions excepting those in the ultra- 

 violet spectrum which are attributable to the phenylalanin and 

 tyrosin radicals. This objection is deprived of force, however, 

 by the fact that in the hydantoins, in which analogous "enoli- 

 zation" does demonstrably occur, no absorption-band is developed. 



