122 



INTRODUCTION TO IMMUNOCHEMICAL SPECIFICITY 



albumin. The constant A'h had in both cases a vahie of about 105, 

 which is consistent with the idea that a carboxyl group, — COO~, 

 is critically involved in the antibody-antigen bond in these systems, 

 and must be ionized for maximum bond strength. Singer concluded 

 that the attraction of this group for its complementary positive group 

 accounts for about half of the strength of the antibody-antigen bond 

 in these cases. The remainder is presumably due to some or all of 

 the other forces mentioned above. 



3.2 



3.6 



pH 



Fig. 9-4. Effect of pH on antibody-antigen equilibrium in the bovine serum 

 albumin system, plotted according to equation (1). The slope of the line is 

 -1.2 (Singer, 1957). 



In the case of the attraction of antibody to /'-(/''azophenylazo)- 

 benzene arsenate, Nisonofif and Pressman (1957) found that the 

 negatively charged - — COO~ group contributed over 4.8 kcal./mole 

 to the binding energy, again indicating the presence of a positive 

 charge in the combining group of the antibody. The uncharged 

 /j-phenylazo group contributed 2.3 kcal./mole. 



There are a number of reasons for believing that the van der Waals 

 forces are among the most important of the non-coulomb forces. One 

 of the arguments supporting this belief derives from the fact that the 



