Reconstitution
When reconstituted at 1 mg/mL in water, solution will contain 0.05 M Tris buffer salts, pH 7.5, 0.2 M NaCl, 0.003 M NaN3, and 0.001 M sodium EDTA. Store reconstituted solutions in the refrigerator.
Stability
The product, as supplied, is stable 3 years when stored properly. Solutions are reported to be stable for 1 year when stored at 2-8°C and will lose biological activity after prolonged exposure to pH below 6 or above 8. DO NOT FREEZE.
Antigen Description
Cholera toxin is the virulent factor from Vibrio cholerae that leads to severe diarrhea followed by dehydration in humans. Several bacterial toxins are ADP-ribosyltransferases with protein substrates. Many of the substrates ADP-ribosylated by bacterial protein toxins are G-proteins, which are involved in signal transduction and ADP-ribosylation is one of the more significant post translational modifications of proteins. The ADP-ribosylation activity of cholera toxin activates adenylate cyclase, resulting in the production of cyclic AMP by adenylate cyclase, which causes many metabolic alterations. Cholera toxin belongs to the AB5–subunit family of toxins. The native hexameric protein has a molecular mass of ~85 kDa and contains two subunits. It consists of a single A subunit (~27.2 kDa), responsible for the ADP-ribosylation activity, and five B subunits (~11.6 kDa each), which are arranged as a pentameric ring with an apparent 5-fold symmetry and are associated with the cell surface receptor binding and subsequent internalization (transmembrane transport) of the enzymatic component. A single isoelectric variant of the cholera toxin has been isolated, which crystallizes readily and reproducibly. Cholera toxin has an isoelectric point (pI) of 6.6. Chromatographic properties, however, suggest a cationic surface is exposed at pH 7.0, which apparently resides in B subunit. The entire hexameric complex is required for toxic behaviour. Choleragenoid, the intact pentamer of B subunits, interacts with a ganglioside GM1 membrane receptor, but cannot activate adenylyl cyclase; whereas, the A subunit alone does not enter the cell. Due to the effect on adenylate cyclase, cholera toxinand its purified A subunit are frequently used for the study of signal transduction mechanisms. In addition,cholera toxin acts as an adjuvant through thestimulation of B lymphocytes.The cholera toxin B subunit alone is used for tracktracing in neurological research, taking advantage of GM1 ganglioside binding and retrograde transport. Tissue culture cells treated with cholera toxin are not killed and tissues of animals do not become necrotic. The B subunit is non-toxic to cells and possesses no intrinsic adenylate cyclase activity. The cholera toxin B subunit (CTB) attaches to cells by binding to ganglioside GM1. As a result, it has been shown to be a good label for microglial cells (due to the enrichment of ganglioside GM1 on their cell surface), but not for oligodendrocytes or astrocytes. The B subunit has been reported to be an excellent tracer for the study of axonal transport using immunohistochemical methods. Recently it has been widely used as a marker of membrane lipid rafts, which are membrane microdomains enriched with cholestrol and sphingolipids. These lipid rafts have an important role in cell signaling and protein trafficking. This product is the active, native cholera toxin (composed of the A and the B subunits). It is a lyophilized powder containing ~5% protein (LowryTCA). When reconstituted with water to a final concentration of 1 mg cholera toxin per ml, the solution will contain 0.05 M Tris buffer salts, pH 7.5, 0.2 M NaCl, 3 mM NaN3, and 1 mM sodium EDTA.
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