Phytohaemagglutinin (PHA, or
phytohemagglutinin) is a
lectin found in plants, especially
beans. PHA actually consists of two closely related proteins, called
Leucoagglutinin (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.
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 a-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.
