The seeds of the jequirity bean contain both non-toxic lectins and several toxic components. These components have been isolated using a variety of conventional techniques, including gel filtration, ion exchange chromatography, and affinity chromatography. The non-toxic and toxic proteins found in the seeds have some similar biological properties. The two major toxins, abrin A and abrin C, as well as the non-toxic lectins, bind to polygalactose affinity gels. Both of the major toxins appear to be dimers of two distinct subunits, similar in molecular weight to another toxin, ricin. The non-toxic lectins are twice the molecular weight of the toxins ¹ . All of these proteins will agglutinate erythrocytes. Initially, crude seed extracts were subjected to DEAE chromatography ² . Five major bands were isolated with different levels of toxicity and agglutinating activities. Generally, the stronger toxic fractions are weaker agglutinins while the weaker toxins are stronger agglutinins. It was later determined that the toxic and non-toxic components can be separated from crude extracts by employing salt precipitation. The non-toxic lectin precipitates with 45% ammonium sulfate. At this concentration the toxic components remain in solution. The toxins can be precipitated by increasing the salt concentration to 100%. Of more than 10 proteins found in the 45% salt fraction, the lectin is the only protein that will bind to Sepharose ®-4B. Different methods have been used to isolate the non-toxic lectin ^1,3,4. The same protein(s) are isolated in each case, although different resolution of isolectins are obtained. The ammonium sulfate fraction containing the toxins has been subjected to ion-exchange chromatography ^5. The two major toxic components have different biological activities. Abrin A is a weaker agglutinin than abrin C. In addition, abrin C is 3-4 times more toxic for BALB/c mice than abrin A. This result contradicts the earlier finding ¹ that the most toxic fraction is only a weak agglutinin. Abrin C also has a stronger affinity for immobilized galactose than abrin A. In spite of the apparent contradiction concerning the agglutinating activity of the toxic components isolated using different techniques, the toxin isolated by Wei and colleagues, and by Osnes and Pihl, has the same apparent molecular weight. The material supplied at this time by EY Laboratories will contain abrin A, abrin C, and the non-toxic lectin. Please contact the technical services department concerning the availability of the individual proteins. The crystal structures of abrin A has been determined to 2.14 Å ⁷, and abrin A-chains and B-chains have been cloned and sequenced ^8,9.

REFERENCES

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3. Olsnes, S., et al. (1974) J. Biol. Chem. 249 : 803-810.
4. Wei, C. H., et al. (1974) J. Biol. Chem. 249 : 3061-3067.
5. Wei, C. H., et al. (1975) J. Biol. Chem. 250 : 4790-4795.
6. Wu, A.M., et al. (1992) J. Biol. Chem. 267 : 19130-19139.
7. Tahirov, T.H., et al. (1995) J. Mol. Biol. 250 : 354-367.
8. Kimura, M. (1993) Biosci., Biotech. Biochem. 57 : 166-169
9. Hung, C.H., et al. (1994) Eur. J. Biochem 219 : 83-87