J Polym Environ
Fig. 4 Active site topology of endoglucanase Cel7B from Humicola
insolens [89]
Table 2 Potential of endoglucanase Cel7B to degrade cellulose
acetate dependent on the degree of substitution (DS)
DS
DPw
Starting material
0.9
31
Cel7B-fragmented
4
1.2
85
5
1.6
138
27
1.9
189
100
2.5
316
306
2.9
387
394
All samples were intensively incubated with an endoglucanase free of acetylesterase activity, and the degradation
was monitored using size exclusion chromatography
(SEC). The DS 0.9 sample was readily degraded from DP
31 to DP 4. With up to DS 1.7 a 50% reduction in DP could
be observed under the experimental conditions. For the DS
1.9 sample the DP reduction was considerably retarded,
namely from DP = 189 to 100, while CA of DS 2.5 was
more or less resistant to Cel 7B action (DP reduction from
3 16 to 306). The accessibility for the endoglucanase was a
clear function of the DS distribution pattern. The decrease
in chain reduction was certainly caused by two factors: the
water-insolubility of the material, and the shielding by
increased amounts of acetyl substituents. In a separate
study, an endoglucanase from N. sicca SB did not hydrolyze the CA main chain with DS of 1.77, but when the
degree of substitution was low (\1.0), the endoglucanase
hydrolyzed the CA main chain [40].
It has been known for a long time that in addition to
cellulose main chain degrading enzymes, acetyl esterases
123
Fig. 5 Size exclusion chromatography (SEC) profiles of watersoluble cellulose acetate (DS 0.7) fragmented by endoglucanase
Cel7B alone (a) and an Aspergillus enzyme mix including acetylesterase activity (b). Note the different scale in RT of Fig. 5a, b due to
the extended degradation by the endoglucanase and acetylesterase
mix (Fig. 5b) in contrast to fragmentation by endoglucanase alone
(Fig. 5a)
play a key role in the biological degradation of CA. Reese
in 1957 speculated on the existence of an esterase, active
on cellobiose octaacetate [9]. A cellulose acetate-deacetylating microorganism for degradation of cellulosic was
described by Yamauchi and Sakai in 1994 [41]. Sakai et al.
[42] observed enzyme activity that released acetic acid
from CA, when a culture supernatant from Neisseria sicca
was incubated with this substrate. The synergistic action of
acetylesterase and endoglucanase was demonstrated by
incubating a CA of DS 0.7 exclusively with an endoglucanase and in parallel with an endoglucanase and an
esterase (Fig. 5). Acting alone the endoglucanase required
at least 72 h to fragment CA with DS 0.7 to a certain end.
When both enzymes were present a drastic reduction in
chain length occurred within the first hour, and no further
reduction in chain length was seen after 24 h. The synergy
in CA degradation between endoglucanase and acetylesterase was also reported by Moriyoshi et al. [43, 44].
Ishigaki and coworkers [45] reported on a bacterial
lipase from Bacillus sp. S2055, which was partly purified
together with cellulase activity. Both enzymes together
were able degrade CA plastic film of DS 1.7. The bacterial
enzymes were compared in their ability to degrade CA with
commercial lipases and esterases. It is interesting to note
that none of the commercial enzymes were able to degrade
CA. The lipase activity was tested with olive oil and the
esterase activity with p-nitrophenyl acetate. Unfortunately
none of the naturally occurring acetylated polysaccharides
were used as reference substrates.
Altaner et al. (2003) [46] isolated an acetyl esterase
from a commercial enzyme preparation. The enzyme
released acetic acid from water-soluble and water-insoluble
cellulose acetates, native and chemically acetylated xylan
as well as acetylated starch. The acetyl esterase specifically