J Polym Environ
Fig. 6 13C NMR carbonyl signals of CA DS 0.7 (bottom) and after
incubation with carbohydrate esterase family 1 enzyme from Aspergillus oryzae (top). Signals of acetyl substituents at C3 and C2
position are missing due to enzyme-aided deacetylation
cleaved off the acetyl substituents from the C2- and C3positions from CAs of DS \ 1.8 and left the acetyl substituents at the C6-positions intact without degrading the
polysaccharide (Fig. 6). The acetyl esterase derived no
advantage from the presence of an endoglucanase; it was
able to function independently from endoglucanase
activity.
Moriyoshi, et al. in 2005 coined the term cellulose
acetate esterase, based on their study on an isolated esterase from Neisseria sicca [44]. The authors investigated the
mode of action by incubation with the model compounds
acetyl-ß-D-glucopyranosides and –galactopyranosides,
substituted in different positions. The main target of the
enzyme was the position C-3 of the glucopyranoside, followed by position C-2. The positions C-4 and C-6 were
deacetylated at slower rates. It is noteworthy that the
deacetylation also included the C-6 position, which
somehow justifies the term cellulose acetate esterase. When
the 2,3,4,6-tetra-O-acetyl-ß-D-galactopyranoside was incubated, the positions C-3 and C-6 were preferably liberated
from their acetyl substituents, and the enzyme exhibited
clear regioselectivity in its deacetylation. The investigation
was not extended by including polymeric CA.
Cellulose acetate was found to be a substrate of several
acetyl xylan esterases (AXE) [47]. Eight AXEs from different carbohydrate esterase (CE) families were tested on
their activity against CA with a degree of substitution of
0.7 and 1.4. The classification of the AXEs into CE families according to their structure by hydrophobic cluster
analysis followed clearly their activity against CA. W