Introduction The anthrax bacillus, (Bacillus anthracis) was the first bacterium shown to be the cause of a disease when in 1877, Robert Koch grew the organism in pure culture, demon- strated its ability to form endospores, and produced experi- mental anthrax by injecting it into animals. The concept on which medical microbiology are based arose from its work on this bacterium (13). At that time, 125 years ago, anthrax was significant mainly as an econo- mically damaging disease of domesticated animals. Today anthrax is important agent of biological terrorism and threats to civilization. B. anthracis causes three forms of di- sease, cutaneous, pulmonary and gastro-intestinal. The pul- monary form is the most dangerous and may lead to death merely one to two days after onset of severe symptoms. This is due to the rapid growth and release of several potent toxins that engage the immune system and promote tissue destruction. Bacillus anthracis Bacillus anthracis is large, non-motile encapsulated gram-positive spore-forming rod, 1–1.2 µm in width and 3–5 µm in length with square or concave ends. Geno- typically and phenotypically it is very similar to Bacillus ce- reus, which is found in soil habitats around the world, and to Bacillus thuringiensis, the pathogen for larvae of Lepidoptera. The three species have the same cellular size and morphology and form oval spores located centrally in a non-swollen sporangium (11). B. anthracis is capable of producing aerobic endospores that are highly resistant to desiccation and capable of sur- viving for decades in soil. Soil is the natural reservoir for B. anthracis, but its mere presence in soil does not necessa- rily result in infection of grazing animals. Under favorable circumstances, spores enter a vegetative phase and multiply to levels high enough to infect grazing herbivores. Anthrax is mainly a disease of animals, but in rare cases, it can spread to people and cause life-threatening illness. B. anthracis may cause a systemic infection in animals causing their death which results in the return of a new aerobic endospores po- pulation. The stability and infectivity of B. anthracis along with its ability to produce a rapidly lethal pneumonia has drawn attention to its potential as a weapon capable of mass casualties (5). Anthrax Toxin The toxigenic properties of B. anthracis were discovered in 1954. Prior to that time, it was assumed that death was due to blockage of the capillaries by large amount of spo- res. But experimentally it was shown that only about 3 x 10 6 cells.ml -1 are necessary to cause death of the animal. These observations led to the conviction that a specific anthrax exotoxin plays a major role in the pathogenesis of disease. Death from anthrax in humans or animals frequently occurs suddenly and unexpectedly. The level of the lethal toxin in the circulation increases rapidly quite late in the di- sease, and it closely parallels the concentration of orga- nisms in the blood. Production of the anthrax toxin is mediated by plasmid pX01, of 110 MDa (16). Anthrax toxin is not single com- pound, but it is complex substance composed of three anti- genically distinct components: Factor I, edema factor (EF), factor II, protective antigen (PA) and factor III, lethal fac- tor (LF). Each component of the toxin is a thermolabile protein with a molecular mass of approximately 80 kDa. 3 REVIEW ARTICLE ANTHRAX TOXIN CHARACTERIZATION Jiří Patočka 1 , Miroslav Špliňo 2 Purkyně Military Medical Academy, Hradec Králové: Department of Toxicology 1 , Department of Epidemiology 2 Summary: The anthrax toxin comprises three proteins. When they work together, they can kill humans, especially after spo- res of the bacteria have been inhaled. One anthrax protein, called protective antigen (PA), chaperones the two other to- xins into human or animal cells and shields them from the body’s immune system. The second, lethal factor (LF), destroys the white blood cells that hosts send in defence. The third toxin molecule, edema factor (EF), hijacks the signaling system in the body. This disrupts the energy balance of cells and leads to them accumulating fluid and complete destroy of cells. Key words: Bacillus anthracis; Anthrax toxin; Structure; Mechanism of action ACTA MEDICA (Hradec Králové) 2002;45(1):3–5