Thionins are small, basic plant proteins, 45 to 50 amino acids in length, which include three or four conserved disulphide linkages. The proteins are toxic to animal cells, presumably attacking the cell membrane and rendering it permeable: this results in the inhibition of sugar uptake and allows potassium and phosphate ions, proteins, and nucleotides to leak from cells [PMID: 3985614]. Thionins are mainly found in seeds where they may act as a defence against consumption by animals. A barley (Hordeum vulgare) leaf thionin that is highly toxic to plant pathogens and is involved in the mechanism of plant defence against microbial infections has also been identified [PMID: 1377959]. The hydrophobic protein crambin from the Abyssinian kale (Crambe abyssinica) is also a member of the thionin family [PMID: 3985614].