Intracellular targeting toxins consist of two parts: A for activity and B for binding, and are known as A-B exotoxins. The B component determines the toxin's cellular specificity and facilitates its attachment to specific cell surface receptors. After the A-B toxin binds to the host cell, it is taken inside by endocytosis and trapped in a vacuole. As the vacuole acidifies, the A and B subunits separate. The A subunit then enters the cell cytoplasm and disrupts a specific internal cellular function.