Phytohaemagglutinin (PHA) 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), 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.
Crystal structure of PHA-L (Protein Data Bank identifier 1FAT)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.