Protein toxins usually secreted from a living bacterium but also released upon bacterial lysis.
Exotoxins divided into three types on the basis of their structure and activities:
Membrane disrupting Toxins "Cytolytic enzymes".
(1) A-B toxins:
These toxins-interfere with cell metabolism.
Each is formed of two portions:
It is translocated into host cells after binding of B portion.