INTERACTION OF ORGANIC MOLECULES WITH PROTEINS 



107 



f^^ ^^^^ 



Fig. 15. Molecular model of 



(CH3)2N— ^ '^— N=N 



— CH2— CHo— C 



/- 



O 



o- 



at maximum extension (top) and with — COO curled back (bottom). 



chains properly, and the cinnamic acid compound (bottom) which has a double 

 bond in the side chain, and consequently cannot be rotated over to one side. 



There actually is a much longer span with the latter than with the former. 

 Consequently, too long a molecule, as well as too short a molecule, will not fit 

 between these protein side chains. 



These specificities, although I have described them, of course, in terms of the 

 organic molecules, the small ones interacting with the protein, reside, presuma- 

 bly, in the protein itself. 



I mentioned at the beginning that if we take a protein molecule such as serum 

 albumin, which carries a negative charge, let us say at pH 7, where the negative 

 charge is approximately 12 units per molecule, and measure the binding of an 

 anionic molecule (Fig. 18), it is bound very substantially despite the fact that 

 the protein has a negative charge which ought to repel it. 



Recently we prepared a molecule which, as you can see in Fig. 18 (lower 



