B. anthracis PA83 is the proteolytically activated in vivo by a furin-like protease to produce a 63kD protein PA63. It is one of the three protein components of anthrax toxin, protective antigen (PA) is the central moiety that mediates the entry of lethal factor and edema factor into the target cell. PA binds to the cell surface via a type I membrane protein with a von Willebrand factor A domain called anthrax toxin receptor.||After inhalation by mammals, Bacillus anthracis spores germinate in alveolar macrophages then migrate to lymph nodes where they multiply. The vegetative bacteria excrete the tripartite exotoxin which consists of three polypeptides: protective antigen (PA, 83kD), lethal factor (LF, 90kD) and oedma factor (OF, 89kD). The two components (OF and LF) of the toxin enzymatically modify substrates within the cytosol of the mammalian cells: The OF is an adenylate cyclase that impairs the host defenses through a variety of mechanisms inhibiting phagocytosis. The LF is a zinc dependent protease that cleaves several mitogen activated protein kinase kinases (MAPKK) and causes lysis of macrophages. To intoxicate mammalian cells, the third component of the toxin PA, binds to a ubiquitously expressed cellular receptor, Tumor Endothelium Marker-8 (TEM8). Upon binding to TEM8, PA is cleaved into 20 and 63kD fragments (PA20 and PA63) by furin or furin-like proteases. PA20 dissociates into medium and allows the PA63 fragment to heptamerize and bind LF and OF of the toxin. The resulting complex of PA63 fragment with EF and/or OF binds to PA-receptor TEM8/ATR and internalized into endosomes followed by translocation of LF and OF into cytosol of the cells.||Applications:|May be used for ELISA or Western Blot as positive control. Not intended for in vivo use. Other applications not tested. ||Recommended Dilutions: |Optimal dilutions to be determined by the researcher. ||Storage and Stability:|Aliquot to avoid repeated freezing and thawing and store at -70°C. Aliquots are stable for 6 months. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap.