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Choleragen, a diarrheagenic protein enterotoxin elaborated by Vibrio cholerae, has been isolated from the supernate of fermenter cultures by steps involving ammonium sulfate precipitation, DEAE cellulose, Sephadex G-75, and Agarose A-5m chromatography. The resulting product appears to be pure according to immunoelectrophoretic, disc electrophoretic, ultracentrifugal, and immunologic criteria. Sephadex gel filtration and membrane filtration studies suggest a molecular size of 61,000. The isolated product is highly active in inducing experimental cholera in infant and adult rabbit models. It also elicits, in small dosage, an increased vascular permeability in skin. These observations indicate that choleragenicity and increased vascular permeability are intimately associated phenomena and may be manifestations of the same basic mechanism. An additional, antigenically identical, protein has also been isolated by the same procedures. The latter substance, termed "choleragenoid", lacks the permeability effect and choleragenicity of the choleragen moiety. Its size (estimated from Sephadex gel filtration at 42,000) is smaller than that of choleragen and it also differs in charge. Choleragenoid may prove useful as a nontoxic immunogen to protect against pathologic effects of V. cholerae infection.

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