Phytohaemagglutinin

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Phytohaemagglutinin (PHA, or phytohemagglutinin) is a lectin found in plants, especially beans. It is found in the highest concentrations in the red kidney bean (Phaseolus vulgaris). It has a number of physiological effects and is used in medical research. In high doses it is a toxin.

The lectin has a number of effects on cell metabolism: it induces mitosis, and affects the cell membrane in regard to transport and permeability to proteins. It agglutinates most mammalian red blood cell types.

As a toxin it can cause poisoning in monogastric animals through the consumption of raw or improperly prepared kidney beans. Measured in haemagglutinating units (hau) a raw kidney bean can contain up to 70,000 hau. This can be reduced around 200-fold by correct cooking. The bean also contains α-amylase inhibitor.

Poisoning can be induced from as few as five raw beans and symptoms occur within three hours, beginning with nausea then vomiting which can be severe and sustained (profuse), then diarrhea. Recovery occurs within four or five hours of onset, usually without the need for any medical intervention.

Medically it is used as a mitogen to trigger synthesis in T-lymphocytes, and to activate latent HIV-1 from human peripheral lymphocytes.

PHA actually consists of two closely related proteins, called PHA-L and PHA-E. The letters E and L point to the fact that these proteins agglutinate Erythrocytes and Leukocytes, respectively.

[edit] References

Hamelryck, T.W., Dao-Thi, M., Poortmans, F., Chrispeels, M.J., Wyns, L. & Loris, R. (1996) The Crystallographic Structure of Phytohemagglutinin-L. J. Biol. Chem., 271: 20479-20485