AB toxin

Multi-subunit toxin in which there are two major components, an active (A) portion and a portion that is involved in binding (B) to the target cell. The A portion can be effective in the absence of the B subunit(s) if introduced directly into the cytoplasm. In the well-known examples, the A subunit has ADP-ribosylating activity. See cholera toxin, diphtheria toxin, pertussis toxin. ...

AB toxin

The AB toxins are two-component protein complexes secreted by a number of pathogenic bacteria. They can be classified as Type III toxins because they interfere with internal cell function. They are named AB toxins due to their components: the `A` component is usually the `active` portion, and the `B` component is usually the `binding` port...
Found on http://en.wikipedia.org/wiki/AB_toxin
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