Chemistry Reference
In-Depth Information
Fig. 4.4
A flow diagram of
a typical multi-step process
adopted for enzyme immo-
bilisation on mesoporous sili-
cas by covalent attachment.
Reproduced with permission
from Springer [
49
]
The engineered cysteine allowed immobilisation via the same site, thus keeping the
same orientation of all immobilised enzyme molecules.
4.3.4 Adsorption
Adsorptive immobilisation of enzymes could involve ionic binding or physical ad-
sorption through weaker interactions. For ionic binding, the enzyme is ionically
bonded onto a support through electrostatic interactions between charged groups
on the enzyme and the support. The charges on the enzyme depend on its confor-
mation, as well as factors such as pH, ionic strength and temperature. Therefore,
depending on these charges, a support with opposite charge can be appropriately
selected [
40
]. In some cases, the support may need pre-treatment to optimise en-
zyme adsorption.
Many of the supports used for covalent binding can also be used for ionic bind-
ing, so long as they have suitable charges. For ionic binding, these supports are
typically referred to as ion exchangers. Polystyrene supports have been shown to
be effective for enzymes such as β-galactosidase, while polyethylenimine (PEI) has
been proven effective for lipase immobilisation [
8
,
41
,
54
].
