460 BACTERIOLOGICAL CHEMISTRY 



if the amino groups of a pui'ifiecl aiiti))0(ly to Type 1 

 pneumococcus were acetylated by the action of ketene, 

 the antibody lost much of its power of reacting with the 

 Type I polysaccharide. If the amino groups are treated 

 with formaldehyde with introduction of methylene 

 groups (see p. 417) the power of reacting is completely 

 lost. Reconstitiition of the amino group by treatment of 

 the methylene derivative with dilute acid at ^^H 4-0 for 

 several days at 0° C. restores the activity. It is, there- 

 fore, very probable that the amino groups of this antibody 

 are involved in its reactions. It is also very probable 

 that the strongly polar carboxyl group of the uronic 

 acid or aldobionic acid of the hapten is involved, since 

 esterification of the Type I polysaccharide with diazo- 

 methane causes complete loss of activity, although it 

 must be remembered that one hydroxyl group and the 

 amino group are also methylated by this procedure. 

 Alkaline hydrolysis, however, removes the ester methyl 

 group but not those attached to the hydroxyl and amino 

 groups, with almost complete restoration of the hapten 

 activity, wliich suggests that it is the carboxyl group 

 which is largely responsible for the action, although the 

 other two groups contribute to some extent. 



It has been suggested that the prominent polar 

 groups in antigens which determine their specificity 

 actually fit into hollows or sockets in the antibody 

 molecules which were modelled round the determinant 

 groups either by the folding mechanism described by 

 Pauling or by the actual selection of appropriately shaped 

 amino-acid groups as in the theories put forward by 

 Breinl and Haurowitz and by Mudd. It is considered 

 that electronegative groups like the carboxyl ion on an 

 antigen molecule would be matched by electropositive 

 groups such as an amino group on the antibody molecule. 

 This is in keeping with the fact that it is the terminal 

 parts of determinant groups which have most influence 

 on specificity, as with the peptide haptens mentioned on 



