Which of the following stimulate adenylate cyclase with G-protein coupled action?
Correct Answer: Cholera toxin
Description: pg no:283 Cholera Toxin :-MOA--cholera toxin have A and B subunits. the B subunit binds specifically to the Gm1 ganglioside receptor on the intestinal epithelial cells. The active A enters the cell and is cleaved in to fragment A1 &A2 .The a2 fragment links the active A1 to the B subunit and thus A1 fragments stimulate the adenylate cyclase activity of the epithelial cell.this inturn conve the ATP into cAMP pg no:250 SHIGA TOXIN --VEROCYTOTOXIN (VT)--it is of two types VT1 which is neutralised by antiserum to shigatoxin and VT2 that resist neutralisation by this antiserum . they are cytotoxic to vero and hela cells enterotoxic in rabbit ileal loop and show paralytic lethality in mouse. VT is also composed of A and B subunits . VT production is found to be phage encoded in several Esch.coli strains Besides VT1 and VT there is another toxin named VT2v toxin differs from VT1 and VT2 in that it is not cytotoxic to Hela cells and is not phage encoded pg no 226 Diphtheria toxin -the pathogenicity is due to production of a very powerful exotoxin by virulent strins of diphtheria bacilli. About 90-95% gravis and intermedius strains are toxigenic , while only 80-85% of mitis strains are so . avirulent strains are frequent among convalescents, carries and contacts . the strain most widely used for toxin production is park -williams 8 strain which has been described as a mitis strain and as an intermedius strain . the toxigenicity of the diphtheria bacillus depend=s on the presence of a tox gene which can be transferred from one bacterium to another by lysogenic bacteriophages , of which beta phage is the most impoant . Non toxic genic strains may be rendered toxigenic by infecting them with beta phage . this process is known as lysogenic conversion . the toxigenicity remains as long as the bacteria is lysogenic . When the bacteria is freed of its phage as by growing in the presence of antiphage serum , it loses the toxigenicity and becomes non toxigenic strain . in addition to beta phage other phage s are also known to carry tox genes Ref:textbook of Microbiology Dr.C.P.Baveja 4th Edition
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