BIOLOGICAL AND ANTIGENIC SPECIFICITY 327 



enolization and say that it consists of the loss of asymmetry by 

 the a carbon atom. Wells* illustrates this as follows: 



OH OH 



II I I 



R— C— C— NH. » R— C = C— NH, 



I ■ I 



CH,, CH, 



Ketone form Enol form 



(Before racemization) (After racemizatioii) 



It -will l)e ol)served tliat in the ketone form the a carbon is 

 linked to four different groups; this makes of it an as>mimetrie 

 carbon atom. In the enol form it is linked to three, and hence is 

 no longer asymmetric and can now form equal amounts of two 

 isomers Avhich accounts for its loss of optical activity, etc. 



Enzyme Action Destroys Antigenic Propp:rty. — It has been 

 quite well established that when proteins are acted upon by 

 enzjmies their antigenic properties are diminished and entirely lost 

 during the process of digestion. 



Relationship of Digestibility and Antigenic Property.— 

 Since racemized proteins are neither antigenic nor digestible by 

 enzymes and since complete ])roteins possess nondiffusible molec- 

 ular aggregates and are both antigenic and digestible, it has 

 been suggested that for antibody production the antigen must 

 reach the surface of the tissue cells and call forth extracellular 

 enzymes. It should be remembered that the molecular aggregates 

 of an antigen may be phagocytized, so to speak, by the retieulo- 

 endothelium and digestion occur within food vacuoles. Anti- 

 bodies could be returned to the general circulation by a process 

 llio reverse of that of phagocytosis. * 



Landstciner does not regard the lack of digestibility of racemized 

 ])roteins as the reason for their lack of an antigenic property but 

 thinks it Ls due to their lack of a chemical structure necessary to 

 stimulate antibody formation. 



Possible Number of Compounds Formed by Amino Acids.— 

 Abderhalden has calculated, according to Wells (1929), ''that 20 

 amino acids could form 2,432,902,008,176,640,000 different com- 

 pounds, and this without including the enormously greater num- 

 ber that might be made by varying the proportion of the different 



•Well.'', H. G. : The Chemical Aspects of Immunity, Reinhokl PublLshing 

 Corporation. 



