200 IMMUNO-CATALYSIS 



acetylated phenolic groups. Failure of this treatment to reactivate the 

 acetylated virus, however, led them to conclude that the inactivation 

 of the virus was not due to acetylation of the phenolic groups. Miller 

 and Stanley (1941) reported that about 70 per cent of the amino 

 groups and 20 per cent of the phenol groups of tobacco mosaic virus 

 could be acetylated without loss of activity. 



Discussing the results of various studies, Olcott and Fraenkel-Conrat 

 (1947) point out the possibility that also some of the aliphatic hydroxyl 

 groups, and groups other than those concerned above, might be in- 

 volved in the treatment of proteins by ketene. It would thus appear 

 that ketene falls short of being a good protein reagent: its action is 

 not specific; it falls short of acetylating completely any or all of the 

 reactive groups; it involves difficult analytical manipulation; it tends 

 to surface denature sensitive proteins; it appears to be extremely toxic, 

 and the racemization of asymmetric carbon atoms of proteins has been 

 indicated. Under these circumstances, the effects resulting from the 

 ketenization of proteins leaves unexplained the specific relationship of 

 various groups with the biological specificities of proteins. 



d. lodination of Proteins. Iodine has often been used as an oxidiz- 

 ing agent in the study of HS-enzymes. In dilute acid solutions, high 

 iodine concentrations specifically oxidize SH-groups. In neutral and 

 alkaline solutions, iodine substitution in the tyrosine groups of proteins 

 occurs. In either treatment, both oxidation and substitution can take 

 place. Upon iodination of proteins in strong ammoniacal solutions, 

 under conditions which have been employed in studying the antigenic 

 properties of proteins, additional impairment such as loss of species 

 specific properties of the whole molecule would be expected to occur. 

 It has been found that the rate of iodination is associated with the 

 degree of denaturation. The rate of iodination of native protein is 

 slower. In urea solution, which favors denaturation, iodination is more 

 rapid, indicating an increased availability of the tyrosine groups for 

 iodination with increasing denaturation. lodination of imidazole 

 groups (histidine) of proteins, and indole groups (tryptophane) may 

 occur in excess of iodine and prolonged treatment. 



lodination of horse serum globulin in alkaline medium, when 

 presumably all tyrosine is substituted in the 3 and 5 positions, caused 

 loss simultaneously both of the ability to react with, and the ability 

 to produce anti-species antibodies (Kleczowski, 1940b). On the other 



