title: Studies of the subunit structure of choleragen.
abstract: The two choleragen protein constituents were isolated and characterized. Protein I has a molecular weight of approximately 54000. It consists of subunits of approximate molecular weight 10000. Protein II with molecular weight of approximately 32000 is cleaved by 2-mercaptoethanol into two fragments, protein II1 (N-terminal Asx, Mr = 25000) and protein II2 (N-terminal Ser, Mr = 7000). Proteins II1 and II2 could be recombined by oxidation to yield protein II. Upon treatment of choleragem with 2-mercaptoethanol protein II1 precipitates quantitatively. The remaining protein consisting of proteins I and II2, was quantitatively precipitated by ganglioside GGtet1. Of the separated choleragen subunit proteins, only protein I and not protein II complexed specifically with ganglioside GGtet1. The isolated proteins I and II were considerably less toxic in the skin test but almost full toxicity was recovered after mixing the two proteins I and II. Antisera against protein I and protein II revealed no immuno-cross reactivity between the two proteins. Both antisera inhibited the biological effects of choleragen in the skin and ileal loop tests. A molecular model for the constitution of choleragen is proposed.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D001426:Bacterial Proteins / Q000032:analysis* / Q000276:immunology; D005779:Immunodiffusion; D046911:Macromolecular Substances; D008623:Mercaptoethanol; D008970:Molecular Weight; D014118:Toxins, Biological / Q000032:analysis*; D014734:Vibrio cholerae / Q000032:analysis*
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D046911:Macromolecular Substances; D014118:Toxins, Biological; D008623:Mercaptoethanol