Biomedical Engineering Reference
In-Depth Information
exonuclease. Cellobiohydrolase I degrades the reducing end, and CBH II degrades
the nonreducing end of the cellulose chain. The second synergy occurs only in
the hydrolysis of natural cellulose, not in the hydrolysis of CMC and HEC. The
enzymatic hydrolysis of endo-1,4-
“
-D-glucanase and exo-1,4-
“
-D-glucanase is a
heterogeneous reaction, while the reaction of
“
-glucosidase hydrolysis cellobiose is
a homogeneous reaction. Endo-1,4-
-D-glucanase has high enzyme activity when
it degrades CMC, but enzyme activity is low when it degrades MCC. Exo-1,4-
“
-D-
glucanase has high enzyme activity when it degrades MCC. Enzyme activity is low
when it degrades CMC.
The effects of synergy are associated with the nature of the substrate. As
the degree of crystallinity increases, the synergistic effect is also enhanced. The
synergistic effect is small when the degree of crystallinity is low and the substrate
is soluble. Synergies between CBH and EG components generally consider that
BG hydrolyzes the inhibitory product of the CBH end and thereby enhances the
functional capacity of the CBH or EG. Cross synergy of the different sources of
cellulase components has been confirmed. If CBH is added to many false cellulose
microorganisms that do not generate CBH, they can degrade natural cellulose.
However, the exact role of the cellulase components in the cellulose hydrolysis
process is still not fully informed, and the synergy theory never shows how the
synergy reaction is carried out; especially, the degradation mechanism of the
cellulose crystalline regions is still not clear. Chanzy et al. [
103
] proved that CBH I
can be combined by cellulose molecular chains randomly through colloidal studies.
Henrissatetal.[
104
] found that, except for the homogenization of MCC, the
enzymolysis capacity of EG I to MCC is low. There is no enzymatic activity of
CBH I on CMC, but there is high degradation ability to MCC. EG I and CBH I can
synergistically degrade filter paper, MCC, homogenized MCC, and bacterial MCC,
but they cannot synergistically degrade
Valonia
cellulose and CMC. CBH II and
EG I or EG II can synergistically degrade insoluble cellulose. CBH I and CBH II
also can synergistically degrade insoluble cellulose. However, it is different from
the best synergy ratio between various enzymes [
104
]. CBH I can even hydrolyze
barley
“
“
-glucan via endoenzymatic hydrolysis. Because 90 % of barley
“
-glucan
is connected with cellotriose, cellulosic tetrasaccharide bonded by
-1,3-glycosidic
linkages, and it also has several amounts of polysaccharide chain composed of ten
consecutive
“
-glucan is similar to CMC. The
difference is that the hydroxyl group of glucose is not replaced by carboxymethyl.
The studies of Nisizawa et al. found that the high degrees of substitution of CMC
had a greater resistance than the low degrees of substitution of the CMC to the
exocellulase. They showed that low activity of CBH I to CMC may be associated
with substituent [
105
].
“
-1,4-glycosidic bonds. Therefore,
“
3.7.3.2
Degradation Mechanism of Basidiomycetes
Some types of basidiomycetes are the main cause of wood decay and can be
divided into two groups: brown pathogens and white pathogens. Brown pathogens
