Enzyme Immobilization on Chitosan-Based Supports - Chitosan Based Hydrogels: Functions and Applications - page 356

OH OH

O

O

HO

O O

HO

NH n

NH 2

Electrospinning CH 3

O

Lipase

GA

Acc V
600 IV

Spol
30

Kaon
6000C

Dct
SE

WD
40

1 m

Dajong UtV

Acc V
600 IV

Spol
30

Kaon
6000C

Dct
SE

WD
40

1 m

Dajong UtV

Figure 8.8
Schematic representation of lipase immobilization on the chitosan nanofibrous electrospun membrane. (From
Huang, X. J., Ge, D., and Xu, Z. K. 2007. Eur Polym J 43: 3710-3718. With permission.)

membrane by GA. This chitosan nanofibrous membrane was used as a support for lipase
immobilization with the advantages of high enzyme loading up to 63.6 mg/g and activity
retention of 49.8%. The stabilities of the immobilized lipase toward pH, temperature, reuse,
and storage were also enhanced [63,64].

8.4 Chitosan Modifications for Enzyme Immobilization
In this section, chitosan modifications for enzyme immobilization broadly include chito-
san derivatives and chemical-grafted chitosan copolymer. An ideal support for enzyme
immobilization should be chosen in order to achieve essential properties such as chemical
stability, hydrophilicity, rigidity, mechanical stability, larger surface area, resistance to
microbial attack, and so on. Without disturbing the degree of polymerizationof chitosan,
one can chemically modify this acquiescent polymer since it provides functional groups
such as primary amine and primary as well as secondary hydroxyl groups in its mono-
mers. Furthermore, one way of improving these properties is by grafting monomers onto
the matrix.
There are a number of reasons for coupling polymers with enzymes. Polymer conjuga-
tion has been reported to reduce the autolysis of proteolytic enzymes and to allow
enzymes to dissolve in nonaqueous solvents. “Smart” biocatalysts have been prepared
by conjugating enzymes to stimuli-responsive polymers that respond to changes in pH,
ionic strength, temperature, redox potential, and light. Moreover, there are numerous
examples in which the enzymes bound to sugars or sugar-based polymers are stabilized.
Although the stabilization mechanism is not understood, it may be due to a reduction of
autolysis (for proteases), MPA that may limit enzyme distortions, or microenvironmen-
tal effects.