Phytohaemagglutinin

Phytohaemagglutinin (PHA, or phytohemagglutinin) is a lectin found in plants, especially certain legumes. PHA actually consists of two closely related proteins, called leucoagglutinin (PHA-L) and PHA-E. These proteins cause blood cells to clump together. PHA-E cause erythrocytes (red blood cells) to clump. PHA-L causes leukocytes (white blood cells) to clump. Phytohaemagglutinin has carbohydrate-binding specificity for a complex oligosaccharide containing galactose, N-acetylglucosamine, and mannose. It is found in the highest concentrations in uncooked red kidney beans and white kidney beans (also known as cannellini), 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. 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 legumes, e.g., beans. Measured in haemagglutinating units (hau), a raw red kidney bean may contain up to 70,000 hau, but this is reduced to between 200 and 400 hau when properly cooked. Studies by British scientists recommend soaking beans for at least five hours, discarding the water, and then boiling the beans in fresh water at for at least thirty minutes. A pressure cooker at 15 psi may be used to cook beans in 45 minutes without presoaking. Insufficient cooking, such as in a slow cooker at 75 °C/ 167 °F, may not completely destroy the toxins. Beans also contain alpha amylase inhibitor, but not in sufficient quantities to affect the digestion of starch after consumption of beans. Poisoning can be induced from as few as four raw beans.