Phytohaemagglutinin

Phytohaemagglutinin (PHA) is a lectin derived from the seeds of the garden bean (Phaseolus vulgaris). It occurs in the form of tetramers composed of two related polypeptides (PHA-L and PHA-E). The markings L and E correspond to leukoagglutination and erythroagglutination abilities of PHA subunits. PHA is used, for example, as a mitogen to stimulate the division of lymphocytes in cytogenetic examinations or to activate latent HIV-1 in peripheral blood lymphocytes.

In high doses, PHA has toxic effects. It is found in the raw or uncooked seeds of a number of legumes. Measured in hemagglutination units (hau), the concentration in raw red beans can be as high as 70 000 hau, while in cooked beans it is only 200-400 hau. Heating the beans to less than 80 °C can increase the toxicity by up to five times, making them much more toxic than when raw. PHA poisoning manifests itself 1 to 3 hours after ingestion nausea and vomitingm.

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