CHAPTER 6 

 Plant Agglutinins (Lectins) II 



Nature of Plant Agglutinins 



There is no reason to suppose that the blood group-specific ag- 

 glutinins for which I proposed the name lectins are essentially dif- 

 ferent from the "nonspecific" agglutinins which have been known 

 so long. Ricin, from Ricinus communis, has been studied more 

 thoroughly than any other of the plant agglutinins. Although a toxin 

 as well as a hemagglutinin, it is, on the whole, a typical lectin. The 

 chemistry and immunology of ricin were studied and reviewed fairly 

 recently by Kabat, Heidelberger, and Bezer (1947) and by Kriipe 

 (1956). It is a globulin (i.e., soluble in salt solutions but not in dis- 

 tilled water), with an isoelectric point of 5.4-5.5 and a molecular 

 weight of about 80,000. It can be crystallized ; the crystalline protein 

 is highly toxic and strongly hemagglutinative. 



The most complete immunochemical study on a specific lectin 

 carried out so far seems to be that of Boyd, Shapleigh, and McMaster 

 (1955). These authors found this anti-A lectin (from lima beans) to 

 be globulin also. They were not able to obtain it in crystalline form 

 but studied concentrated and partially purified preparations of which 

 about 36 per cent were specifically reactive with A antigen. The 

 partially purified material was electrophoretically heterogeneous but 

 nearly homogeneous in the ultracentrifuge. The observed sedimenta- 

 tion constant suggested a molecular weight of about 80,000. 



Boyd and co-workers observed that the lectins, in addition to 

 their ability specifically to agglutinate erythrocytes of the appropriate 

 blood groups, precipitate specifically with the purified antigens (Boyd 



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