3. As it is a cell-free system, there is no transport barrier such as cell membrane for
the substrate or product.
4. The isolation and recovery of the product are simpler and easier.
5. Not only the product but the system itself is stable.
Example Production of glucose isomerase, penicillin acylase.
16.7.3 Whole Cells
Isolated immobilized enzyme systems are easily available commercially and have
advantages of their own. However, the need of a cofactor for the specific reaction
adds complications to the process. The whole cell systems have complete machinery
for enzymes thus they overcome the disadvantage of co-factors. This system is also
environmental friendly and cheaper than isolated enzyme systems. However, the
major disadvantages of the system are then tiresome work-up due to large volumes,
low productivity due to lower concentration tolerance, the formation of more than
one product due to side reactions, and cell membrane as a barrier for biomolecule
transportation.
Example The production of aromatic alcohol 2-phenylethanol (2-PE) from l-phenylalanine (l-Phe) in yeast. The use of whole cells for production of the suitable
product can be performed in the form of growing cells or non-growing cells.
16.7.4 Growing Cells
Growing whole cell system is the most common type of production systems. Here
the desired cells are cultivated in a suitable medium. A concentrated substrate is
added to the culture only after a certain growth of the cells in the media. Sometimes,
emulsifiers (Tween, organic solvents) are added to solubilize substrates and/or
products as in case of steroid biotransformation. The substrate conversion to the
product can be monitored by spectroscopic or chromatographic techniques. Biotransformation can be terminated when the product formation is optimum.
16.7.5 Non-growing Cells
During the non-growing cell biotransformation process, the cell growth (the enzyme
manufacturing phase) and production phase are separated. Substrates are converted
to the desired products by resting or non-growing cells. It is a preferred method for
biotransformation reactions due to the following advantages:
1. A very high substrate concentration can be used as the cell growth stops at this
concentration.
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353
the substrate or product.
4. The isolation and recovery of the product are simpler and easier.
5. Not only the product but the system itself is stable.
Example Production of glucose isomerase, penicillin acylase.
16.7.3 Whole Cells
Isolated immobilized enzyme systems are easily available commercially and have
advantages of their own. However, the need of a cofactor for the specific reaction
adds complications to the process. The whole cell systems have complete machinery
for enzymes thus they overcome the disadvantage of co-factors. This system is also
environmental friendly and cheaper than isolated enzyme systems. However, the
major disadvantages of the system are then tiresome work-up due to large volumes,
low productivity due to lower concentration tolerance, the formation of more than
one product due to side reactions, and cell membrane as a barrier for biomolecule
transportation.
Example The production of aromatic alcohol 2-phenylethanol (2-PE) from l-phenylalanine (l-Phe) in yeast. The use of whole cells for production of the suitable
product can be performed in the form of growing cells or non-growing cells.
16.7.4 Growing Cells
Growing whole cell system is the most common type of production systems. Here
the desired cells are cultivated in a suitable medium. A concentrated substrate is
added to the culture only after a certain growth of the cells in the media. Sometimes,
emulsifiers (Tween, organic solvents) are added to solubilize substrates and/or
products as in case of steroid biotransformation. The substrate conversion to the
product can be monitored by spectroscopic or chromatographic techniques. Biotransformation can be terminated when the product formation is optimum.
16.7.5 Non-growing Cells
During the non-growing cell biotransformation process, the cell growth (the enzyme
manufacturing phase) and production phase are separated. Substrates are converted
to the desired products by resting or non-growing cells. It is a preferred method for
biotransformation reactions due to the following advantages:
1. A very high substrate concentration can be used as the cell growth stops at this
concentration.
16 Biotransformation: Basics and Applied Perspectives
353