Unlike enzyme immobilization, where the enzyme is attached to a solid support (such as calcium alginate or activated PVA or activated PEI), in immobilized whole cell systems, the target cell is immobilized.
Such methods may be implemented when the enzymes required are difficult or expensive to extract, an example being intracellular enzymes.
[1][2] Also, if a series of enzymes are required in the reaction; whole cell immobilization may be used for convenience.
This is only done on a commercial basis when the need for the product is more justified.
Furthermore, intracellular enzymes need not be extracted prior to the reaction; they may be used directly.