Phytohaemagglutinin

Phytohaemagglutinin (PHA, or phytohemagglutinin) is a lectin found in plants, especially beans. 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. It is found in the highest concentrations in uncooked red kidney beans and white kidney beans (also known as cannellini),^[1] and it is also found in lower quantities in many other types of green beans and other common beans (Phaseolus vulgaris), as well as broad beans (Vicia faba) such as fava beans.^[2] It has a number of physiological effects and is used in medical research. In high doses it is a toxin.

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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, such as humans, through the consumption of raw or improperly prepared kidney beans. Measured in haemagglutinating units (hau) a raw red kidney bean can contain up to 70,000 hau. This can be reduced around 200-fold by correct cooking (boiling for at least ten minutes).^[3] Cooking at 80 Celsius can raise the available hau up to five-fold. The bean also contains α-amylase inhibitor.^{[citation needed]}

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 cell division in T-lymphocytes, and to activate latent HIV-1 from human peripheral lymphocytes. PHA-L is used by neuroscientists to trace the path of efferent axons of neurons. This usage is called the anterograde labeling method.^[4]

Notes

References

1. ^ Kidney Beans. The world's healthiest foods. Retrieved on 2007-11-05.
2. ^ Foodborne Pathogenic Microorganisms and Natural Toxins Handbook:Phytohaemagglutinin. United States Food and Drug Administration. Retrieved on 2007-11-06.
3. ^ David Burton. "Undercooked Beans Can Cause Illness", University of Missouri. Retrieved on 2007-11-06. 
4. ^ Carlson, Neil R. (2007). Physiology of Behavior, 9th ed.. Boston: Pearson Education, Inc., 144. ISBN 0-205-46724-5. 

• Hamelryck T, Dao-Thi M, Poortmans F, Chrispeels M, Wyns L, Loris R (1996). "The crystallographic structure of phytohemagglutinin-L". J Biol Chem 271 (34): 20479-85. PMID 8702788.