CHAPTER 9 



Union of Antibody with Antigen : 

 Thermodynamics 



The exact mechanisms by which antibodies produce their effects 

 have not been cleared up in all cases, but that the first step is com- 

 bination of the antibody and antigen is not in dispute. It is therefore 

 of interest to inquire into the forces involved and the firmness of 

 the union. A proper treatment of these points will require the intro- 

 duction of a few elementary thermodynamic notions. 



Forces Involved 



Landsteiner (1936) pointed out that the covalent bond (e.g., 

 the bond holding the two carbons together in ethane, H3C — CH3) 

 does not generally form fast enough and is not reversible enough 

 to be a plausible explanation of antibody-antigen reaction and that 

 some compounds which can react with antibodies cannot form covalent 

 bonds. Similar arguments probably rule out the coordinate link or 

 semipolar double bond. 



We are left with three possibilities : coulomb forces, van der Waals 

 forces, and hydrogen bonding. Coulomb forces are those causing 

 positive and negative charges to attract each other. All antibodies 

 and many antigens are proteins, and it is pertinent to remark that 

 prominent among the charged groups in protein molecules are the 

 positive free e-amino groups ■ — NH3+ of lysine and the negatively 

 charged free carboxy groups — COO~ of the dicarboxylic amino 

 acids such as aspartic acid. A separated, fixed, pair of positive and 

 negative charges constitutes a dipole. It is easy to see how dipoles 



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