PLANT AGGLUTININS (LECTINS) I 65 



Grabar (1947) suggests that the power of plasma proteins to 

 combine with various substances explains one of their important 

 roles — that of carrier (transportcitr). According to his view, the 

 lipid carrying role of beta globulins is analogous to the function of 

 antibodies in their union with antigens. 



Plant Agglutinins 



Possession of proteins capable of such firm and relatively specific 

 combination with other substances is not confined to the higher ani- 

 mals. It has long been known that extracts of certain plant seeds will 

 bring about the agglutination of animal erythrocyte suspensions to 

 which they are added. In fact, the agglutinative action of extracts of 

 the castor bean, Ricinus communis (Table 5-1), was discovered be- 



TABLE 5-1 



Agglutination of Animal Erythrocytes by Ricin* 



^ Numbers indicate degree of agglutination; 4 indicates complete agglutination, 

 0.5, weak agglutination, 0, no agglutination. 



fore agglutinins for erythrocytes were demonstrated in the blood 

 of animals (Lau, 1901), and was described soon after bacterial ag- 

 glutination. Extracts of other plant seeds, such as Abrus precatorius 

 and certain other Leguminosae, were shown to have similar action. 

 Because these plant agglutinins act on the red cells of several 

 animal species they were called nonspecific by many workers. Yet 

 Landsteiner (1945) observed that the substances are not without a 

 certain degree of specificity. He illustrated this fact with a little table 

 in his book on the specificity of serological reactions (Table 5-2). It 



