ANTI-ENZYME IMMUNITY 199 



also with tryptophane (Herriott, 1935), and -SH groups (Fraenkel- 

 Conrat, 1944). With native egg albumin, the reaction is faster with 

 the NH2 than the SH group. In lactogenic hormone (Li and Kalman, 

 1946) the phenolic groups react with ketene faster than do free amino 

 groups; in insulin amino groups are attacked more rapidly than phenol 

 groups (Stem and White, 1938); and in parathyroid hormone (Wood 

 and Ross, 1942) both the amino and phenolic groups are only about 

 40 per cent acetylated. In diphtheria toxin (Pappenheimer, 1938) the 

 presence of amino groups of different reactivity with ketene has been 

 indicated. Extensive treatment of tobacco mosaic virus with ketene 

 fails to acetylate all the amino groups (Miller and Stanley, 1941). 

 Boor and Miller (1939) found that freshly ketenized gonococcus 

 still retained enough toxin to kill two out of six mice, but after standing 

 a week in the cold, the preparation killed six out of six mice, indicating 

 the reversibility of the reaction of ketene with gonococcus. After short 

 acylation at pH 6 to 7 with ketene (Goldie, 1937; Pappenheimer, 

 1938) diphtheria toxin lost its toxicity without losing its ability to 

 combine and flocculate with antitoxin. During the detoxication a 

 number of free amino groups were acetylated, corresponding closely 

 to the number of e-amino groups of lysine present (5.3 per cent). 

 Acylation also of the tyrosine-OH groups caused the loss of the ability 

 of the toxin to combine with antitoxin. Little and Caldwell (1942, 

 1943) found that acetylation of the amino groups of a-amylase with 

 ketene deprived it of enzyme activity. Sulfhydryl and phenolic groups 

 (tyrosine) groups were of little, if any, significance. Amylase was also 

 inactivated by formaldehyde, phenylisocyanate and nitrous acid, which 

 indicated that the primary amino groups were involved. On the other 

 hand, Sizer (1945) finds that the action of ketene, nitrous acid, 

 phenylisocyanate, formaldehyde, oxidants and reductants on chymo- 

 trypsin causes no inactivation, indicating that the primary amino, 

 sulfhydryl or disulfide groups are not required for chymotrypsin 

 activity. In tobacco mosaic virus, ketene or phenylisocyanate have been 

 reported (Schramm and Miiller, 1940, 1942) to react first with the 

 free amino groups; later the phenol and indole groups are affected. 

 Only the reaction with phenol and indole groups has been observed 

 to be associated with loss of infectivity. The disappearance of the NH2 

 group with these reagents is said to be without any effect on the in- 

 fectivity of the virus. Alkaline treatment is expected to hydrolyze the 



