ANTI-ENZYME IMMUNITY 201 



hand, the treatment of proteins with phenyHsocyanate, forming 

 R— NH— CO— NH— <( y derivatives, or with formaldehyde only 

 slightly reduced their affinity toward homologous antibodies. This was 

 interpreted to indicate that amino groups of the antigenic proteins 

 are not involved in combination with antibody (Kleczowski, 1940). 

 As may be recalled from the preceding discussion on acetylation of 

 proteins, the acetylation of the OH groups of tyrosine in diphtheria 

 toxin was reported to cause the loss of the toxin's ability to combine 

 with antitoxin (Pappenheimer, 1938). Due to technical difficulties, 

 the loss or presence of the original species specificity of the acetylated 

 toxin could not be determined. In connection with the results with 

 iodinated proteins of Kleczowski, it must be remembered that substi- 

 tution in positions 3 and 5 of tyrosine in proteins with diazonium 

 haptenic radicals does not cause loss of the ability of the substituted 

 proteins to produce anti-species antibodies. 



Anson and Stanley (1941) reported that the treatment of tobacco 

 mosaic virus with iodine, causing abolition of the sulfhydryl groups 

 does not inactivate the viral activity. If enough iodine is added to the 

 virus, or if the reaction is carried out at a sufficiently high temperature, 

 converting the tyrosine groups into di-iodotyrosine groups, the viral 

 activity is lost. Sizer (1945) found that likewdse the activities of chymo- 

 trypsin and phosphatase are destroyed if tyrosine groups are destroyed. 

 Strong oxidants, likewise iodine, inactivated chymotrypsin, involving 

 the oxidation of its tyrosine groups. Herriott (1937) reported that 

 iodinated pepsin is practically inactive when the number of iodine 

 atoms per molecule of pepsin is 35 to 40. Since there are 16 tyrosine 

 residues (mols) per mole of pepsin, the number of iodine atoms found 

 in iodinated pepsin corresponds to complete di-substitution of all 

 the tyrosine molecules, or three to eight atoms of iodine more than 

 required by theory. 



In evaluating the above considered data one must, no doubt, keep 

 in mind that in addition to the substitution of iodine in the tyrosine 

 molecules, other substitutions and the oxidation of SH groups, under 

 the experimental conditions used, and also the denaturation of the 

 protein molecule, would be expected to occur. 



e. Reactions with Sulfhydryl and Disulfide Groups of Proteins. 

 It is known that the -SH ^ -S-S- relationship in certain enzyme 



