A new approach for the immobilization of permeabilized brewer's yeast cells in a modified composite polyvinyl alcohol lens-shaped capsule containing montmorillonite and dimethyldioctadecylammonium bromide for use as a biocatalyst

Article abstract of DOI:10.1016/j.procbio.2010.05.021

Permeabilized brewer's yeast cells were immobilized in modified composite polyvinyl alcohol lens-shaped capsules containing montmorillonite (MONT) and dimethyldioctadecylammonium bromide (DDAB). The special properties of the capsules were then investigated. The results showed that the diffusion capability of hydrophobic molecules from bulk solution into the capsules was obviously improved by the introduction of 0.5% MONT and 0.05% DDAB into the 15% PVA matrix. More importantly, when ethyl 4-chloro-3-oxobutanoate (COBE) was reduced with the capsules as the biocatalyst, the yield and enantiomeric excess (ee) of the product reached 88% and 99.1%, respectively, within 8. h, which are significantly higher totals than those mediated by the unmodified PVA capsules under the same conditions. The intracellular alcohol dehydrogenase (ADH) in the capsules retained over 81% of its original activity after 1 month of storage and 88% of its initial activity after 20 cycles of reaction.

Full text of DOI:10.1016/j.procbio.2010.05.021

Process Biochemistry 45 (2010) 1445–1449
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Process Biochemistry
journal homepage: www.elsevier.com/locate/procbio
A new approach for the immobilization of permeabilized brewer’s yeast cells in a
modified composite polyvinyl alcohol lens-shaped capsule containing
montmorillonite and dimethyldioctadecylammonium bromide for use as a
biocatalyst
Geng-Hao Gonga, Yi Houa, Quan Zhaoa, Ming-An Yua,∗, Fei Liaob, Lan Jiangc, Xiao-Lan Yanga
a College of Pharmaceutical Science, Chongqing Medical University, #1, Medical College Road, Chongqing 400016, China
b Chongqing Key Laboratory of Biochemistry and Molecular Pharmacology, Chongqing Medical University, Chongqing 400016, China
c College of Environmental and Biological Engineering, Chongqing University of Technology and Business, Chongqing 400067, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Permeabilized brewer’s yeast cells were immobilized in modified composite polyvinyl alcohol lens-
shaped capsules containing montmorillonite (MONT) and dimethyldioctadecylammonium bromide
(DDAB). The special properties of the capsules were then investigated. The results showed that the diffu-
sion capability of hydrophobic molecules from bulk solution into the capsules was obviously improved
by the introduction of 0.5% MONT and 0.05% DDAB into the 15% PVA matrix. More importantly, when
ethyl 4-chloro-3-oxobutanoate (COBE) was reduced with the capsules as the biocatalyst, the yield and
enantiomeric excess (ee) of the product reached 88% and 99.1%, respectively, within 8 h, which are sig-
nificantly higher totals than those mediated by the unmodified PVA capsules under the same conditions.
The intracellular alcohol dehydrogenase (ADH) in the capsules retained over 81% of its original activity
after 1 month of storage and 88% of its initial activity after 20 cycles of reaction.
Received 25 October 2009
Received in revised form 16 May 2010
Accepted 17 May 2010
Keywords:
Permeabilized brewer’s yeast
Immobilization
Modified composite PVA
Diffusion capability
Ethyl (S)-4-chloro-3-hydroxybutanoate
Biocatalyst
© 2010 Elsevier Ltd. All rights reserved.
1. Introduction
higher operational stability and storage stability is very necessary.
However, mass transfer is one of the major factors affecting the
Nowadays, biocatalysts are indispensable tools for the pro-
duction of chiral alcohols whether they are whole cells [1],
permeabilized cells [2–5] or isolated enzymes [6]. When compared
with whole cells, permeabilized cells allow for the use of an exter-
nally added cofactor for efficient catalysis, cofactor recycling, easy
substrate access and easy product release [3]. When compared
with the isolated enzyme, permeabilized cells are cheap and easily
available in large amounts. However, when the permeabilized cells
were reused under the same conditions, the intracellular enzyme
activities in permeabilized cells and the production yield of the
bioreduction process significantly decreased when compared with
the previous batch [3]. Therefore, the use of immobilization tech-
niques to produce a new biocatalyst with good enzyme stability,
activity and effectiveness of immobilized cells because substrates
and products have to be transported through the external bound-
ary layers (external mass transfer) and within the matrix (internal
mass transfer) [7].
Recently, attempts have been made to solve this problem by
the introduction of new techniques that are able to adjust the size
(microbeads) and shape (lenticular shape) of PVA hydrogels [8–11].
Although this method has proven successful, the PVA hydrogel
is highly hydrophilic due to the abundance of hydroxyl pendant
groups on its chains and is thus likely to limit the mass trans-
fer of some organic compounds from the reaction mixture into
the hydrogel layer. The main cause of diffusion limitations may
be due to the fact that organic compounds contain hydrophobic
groups, which are either totally insoluble or very sparsely solu-
ble in the water-soluble gel matrix. To overcome this limit, two
substances, montmorillonite (MONT) and dimethyldioctadecylam-
monium bromide (DDAB), a cationic lipid [12], were introduced
into the PVA matrix.
Abbreviations:
PVA, polyvinyl alcohol; MONT, montmorillonite; DDAB,
dimethyldioctadecylammonium bromide; ADH, alcohol dehydrogenase; ee, enan-
tiomeric excess; COBE, ethyl 4-chloro-3-oxobutanoate; (S)-CHBE, ethyl (S)-4-
chloro-3-hydroxybutanoate; (R)-CHBE, ethyl (R)-4-chloro-3-hydroxybutanoate;
NAD, nicotinamide adenine dinucleotide; CTAB, cetyltrimethylammonium bromide.
MONT is one of the widely used silicate minerals for the prepa-
ration of polymer/mineral composites. MONT belongs to a class
of natural bentonite clay and has some reactive hydroxyl groups
on its surface [13]. During the last decade, polymer/clay nanocom-
∗
Corresponding author. Tel.: +86 23 68485077; fax: +86 23 68485161.
E-mail address: minganyu666@yahoo.com.cn (M.-A. Yu).
1359-5113/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.procbio.2010.05.021

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G.-H. Gong et al. / Process Biochemistry 45 (2010) 1445–1449
posites have attracted a lot of attention because they frequently
exhibit unexpected properties. Polymer-layered silicate nanocom-
posites, which are representative of these materials, consist of 1-nm
thick aluminosilicate layers dispersed in a polymer matrix. These
nanometric fillers can greatly improve the thermomechanical and
barrier properties of polymers with low clay content in compari-
son with unfilled polymers or more conventional microcomposites
[14,15]. It has been found that when the silicate layers are exfoli-
ated (i.e., individually dispersed) in the polymer matrix, maximum
enhancement of the properties is attained [16]. Moreover, surfac-
tants can also bind to the clay mineral, and the surface of the clay
mineral becomes more hydrophobic [13,17].
In this paper, we first report the effects of the addition of
MONT and DDAB into the PVA matrix on the immobilization of
permeabilized brewer’s yeast cells, including changes in the intra-
cellular ADH activity and in the diffusion capacity of hydrophilic
and hydrophobic molecules. Reusability and storage stability of
the immobilized cells and the bioreduction of ethyl 4-chloro-3-
oxobutanoate (COBE) to ethyl (S)-4-chloro-3-hydroxybutanoate
((S)-CHBE) by the immobilized cells were also investigated in a
batch reaction before and after the addition of MONT and DDAB
into the PVA matrix.
Fig. 1. Remaining lactose in an aqueous solution after lactose from bulk solution
diffuses into the PVA capsules. Unmodified PVA capsules (ꢀ). Modified composite
PVA capsules containing DDAB: 0.05% (w/v) ( ); 0.1% (w/v) (
0.3% (w/v) ( ); 0.5% (w/v) ( ).
); 0.2% (w/v) (
);
distance between the needle and the plate was 2 cm) and the plate was immersed
in a 2% (w/v) boric acid solution for 20 min. The plate was then removed from the
solution and left at room temperature for 90 min to allow the gelation process to
be completed. The new modified composite PVA lens-shaped capsules loaded with
permeabilized brewer’s yeast cells were transferred to 100 mM sodium sulfate for
re-swelling. After 12 h, this solution was replaced with 50 mM Na2HPO4/KH2PO4
buffer, pH 7.5. The capsules were stored in this buffer at 4 ◦C. Test groups A, B, C,
D and E are the new modified composite PVA lens-shaped capsules loaded with
permeabilized brewer’s yeast cells and contain different amounts of DDAB (0.05%,
0.1%, 0.2%, 0.3% and 0.5% (w/v), respectively). The capsules of control group F were
prepared following the method described above except that the modified composite
PVA gel matrix was replaced with PVA alone as the immobilization matrix for cells.
2. Materials and methods
2.1. Chemicals
Polyvinyl alcohol with an average degree of polymerization of 1799 50 was
purchased from Shanghai Chemical Reagent Co. (Shanghai, China). Montmorillonite
was supplied by Fenghong Clay Chemicals Co. Ltd. (Zhejiang, China). Lactose and
l-glycine were purchased from Beijing Dingguo Biotechnology Co. Ltd. (Beijing,
China). Dimethyldioctadecylammonium bromide, NAD+, and ethyl 4-chloro-3-
hydroxybutanoate [(R)- and (S)-enantiomers] were purchased from Sigma–Aldrich
(St. Louis, MO, USA). Separated fresh brewer’s yeast cells (a strain of Saccharomyces
cerevisiae) were obtained from Chong Qing Beer Group Ltd. (Chongqing, China). All
other chemicals used were of reagent grade except where noted.
2.5. Diffusion capabilities of hydrophilic and hydrophobic molecules through the
lens capsule
The diffusion capabilities of hydrophilic (lactose and l-glycine) and hydropho-
bic (benzyl benzoate) molecules from bulk solution into capsule A, B, C, D, E or F
were measured in a conical flask, which was placed in an orbital water bath shaker
at 30 ◦C and shaken at 125 rpm. A 50 ml aqueous solution of 0.5% (w/v) lactose or
0.02% (w/v) l-glycine or an isopropanol solution (isopropanol:water = 1:3) of 0.4%
(w/v) benzyl benzoate was added to the flask and a definite amount of capsule A, B,
C, D, E or F was added to the solution. The solute concentration in the solution would
decrease over time because the solute would diffuse from the solution into the cap-
sules. By measuring the change in concentration over time, the diffusion capacity
can be determined. During the initial 5 min, samples from the bulk solutions were
taken every 1 min. The time intervals were subsequently increased to 5 min and
10 min between 5–30 min and 30–60 min, respectively. After enough time, the con-
centration in the bulk solution and the concentration inside capsule A, B, C, D, E or
F would be close to equilibrium. All the experiments were carried out in triplicate
and the mean values were shown in the corresponding Figs. 1–3.
2.2. Permeabilization of fresh brewer’s yeast cells
Fresh brewer’s yeast cells were separated by centrifugation from fresh brewer’s
yeast slurry, which was a by-product from the brewery with a solid content of about
20% and received after beer production from the Chongqing Beer Group Co. Ltd.
(Chongqing, China). Fresh brewer’s yeast cells were harvested by centrifugation at
2016 × g for 10 min. The yeast pellet was again diluted 2–3 times with 0–2 ◦C saline,
screened on a sieve shaker equipped with a 100 mesh screen and centrifuged at
5600 × g for 20 min to obtain the separated fresh brewer’s yeast cells. Dead and live
cells were then examined according to our previous report [4]. The percentage of
live cells is represented as the average of these three determinations.
When the total number of live cells reached 95%, the cells were permeabi-
lized with cetyltrimethylammonium bromide (CTAB) according to the previously
described method [18]. About 2 g of wet yeast cells was uniformly suspended in
10 ml of permeabilization solution containing 0.2% CTAB (w/v) in 0.1 M sodium phos-
phate buffer, pH 7.5. The yeast cells were kept in this solution for 15 min at 24 ◦C with
intermittent shaking. The cells were then separated by centrifugation at 5600 × g for
10 min. The yeast pellet was washed twice with the above-mentioned sodium phos-
phate buffer. After centrifuging and washing, the permeabilized brewer’s yeast cells
were stored at 4 ◦C for further use.
2.3. Preparation of modified composite PVA gel matrix
PVA (15 g) and MONT (0.5 g) were added to water (100 ml) with stirring, and
the mixture was heated to 95 ◦C for 3 h until the PVA particles were completely
dissolved. The suspension was then equally divided into five aliquots (20 ml each),
each of which was mixed with a certain amount of DDAB (0.05%, 0.1%, 0.2%, 0.3%
and 0.5%, w/v) with mild stirring for 5 min. After homogenization for 100 min at
80 ◦C, the temperature of these modified composite PVA gel matrices was allowed
to decrease to 25 ◦C for further use.
2.4. Immobilization of permeabilized brewer’s yeast cells into modified composite
PVA lens-shaped capsules
Fig. 2. Remaining l-glycine in an aqueous solution after l-glycine from bulk solution
diffuses into the PVA capsules. Unmodified PVA capsules (ꢀ). Modified composite
The immobilized cells were prepared as described previously with some mod-
ifications [11]. Briefly, about 2 g of permeabilized brewer’s yeast cells (wet weight)
were added to 10 ml of modified composite PVA gel matrix. The resulting mixture
was dropped on a smooth polystyrene plate using a 9-gauge needle syringe (the
PVA capsules containing DDAB: 0.05% (w/v) ( ); 0.1% (w/v) (
0.3% (w/v) ( ); 0.5% (w/v) ( ).
); 0.2% (w/v) (
);

G.-H. Gong et al. / Process Biochemistry 45 (2010) 1445–1449
1447
razor blade in a Petri dish containing 5 ml of 0.1 M sodium phosphate buffer, pH
7.5. Subsequently, the suspension of immobilized cells was homogenized by grind-
ing slightly with a mortar and pestle. Finally, the suspension of immobilized cells
(the capsule concentration: 0.02 g/ml) was obtained (Sample 1). As a comparison
group, free yeast cells were suspended in 0.1 M sodium phosphate buffer, pH 7.5 at
a cell concentration of 0.2 g/ml (Sample 2). The ADH activity of the two groups of
cells was determined using a previously described method [21]. Generally, 1.5 ml of
0.1 M sodium pyrophosphate buffer, 0.5 ml of 2 M ethanol and 1 ml of 20 mM NAD+
solution were mixed in a test tube and then added to Sample 1 (0.1 ml) or Sample 2
(0.1 ml). The ADH activity was determined by measuring the steady state increase
in the rate of absorbance change at 340 nm that results from the reduction of NAD+.
One unit of ADH activity was defined as the amount of enzyme required to reduce
1 ␮mol of NAD+ per min at 25 ◦C and pH 7.5.
2.10.3. Analysis of reactant and products
At the end of the reaction, experimental procedures were carried out as previ-
ously described with some modifications [4]. Briefly, the capsule-immobilized cells
separated from the reaction mixture described above were washed with deionized
water. The remaining reaction mixture was centrifuged at 4160 × g for 15 min at 4 ◦C.
The combined supernatant and filtrate were extracted twice with ethyl acetate. The
combined organic layer was washed first with saturated sodium bicarbonate and
then with saturated brine, dried over anhydrous magnesium sulfate and filtered. The
concentrations of COBE, (R)-CHBE and (S)-CHBE were determined on a Varian 3800
GC equipped with a FID detector (Varian, Darmstadt, Germany). A Chiraldex-GTA
capillary column was used (20 m, 0.25-mm i.d.; Advanced Separation Technologies
Inc. (Astec), Whippany, New Jersey, United States). Acetophenone was used as an
internal standard.
Fig. 3. Remaining benzyl benzoate in a water/isopropanol system after benzyl ben-
zoate from bulk solution diffuses into the PVA capsules. Unmodified PVA capsules
(ꢀ). Modified composite PVA capsules containing DDAB: 0.05% (w/v) ( ); 0.1% (w/v)
(
); 0.2% (w/v) (
); 0.3% (w/v) ( ); 0.5% (w/v) ( ).
2.6. Effects of pH and temperature on intracellular ADH activity
To determine the effect of the change in pH on the ADH activity of free or immo-
bilizedcells, the freeor immobilizedcells were uniformlysuspended in 0.1 M sodium
phosphate buffer (pH 5.0–10.0) and incubated at 30 ◦C for 30 min. The effect of
temperature on the ADH activity of free or immobilized cells was determined by
varying the incubation temperature of the suspension from 10 ◦C to 50 ◦C at pH 7.5
for 30 min. The ADH activity of each sample was determined at least three times.
The relative ADH activity was calculated as a percentage of its maximum activity.
3. Results and discussion
3.1. Diffusion capabilities of hydrophilic and hydrophobic
molecules through the lens capsule
2.7. Bioconversion of COBE to (S)-CHBE by capsule-immobilized cells
The diffusion capabilities of different solutes from bulk solution
into the PVA capsule-immobilized cells are all shown in Figs. 1–3.
These solutes of low molecular weight are either hydrophilic or
hydrophobic and include lactose (Fig. 1), l-glycine (Fig. 2), and ben-
zyl benzoate (Fig. 3). All data were measured at least three times
and the average values are shown in the figures.
An appropriate amount of capsule-immobilized cells with modified compos-
ite PVA or unmodified PVA was added to reaction flasks containing 30 ml of 0.1 M
phosphate buffer, pH 7.5; MgCl2 and NAD+ were added to final concentrations of
15 mM, and 0.1 M, respectively. Next, 2.5 ml of 2-propanol was added, followed
by dilution with redistilled water to the final volume of 37.5 ml. The reaction was
started by 12.5 ml of COBE/n-butyl acetate (COBE:n-butyl acetate = 1:3 v/v), which
was continuously fed into the stirred suspension at a rate of 5 drops/min. Flasks
were incubated in a 30 ◦C water bath for 8 h with continuous shaking at 125 rpm.
The concentration of COBE, ethyl (R)-4-chloro-3-hydroxybutanoate ((R)-CHBE)) and
(S)-CHBE were measured by gas chromatography (GC) at 1-h intervals as described
in Section 2.10.3.
First, we looked at the diffusion capabilities of hydrophilic
molecules in the aqueous system. As shown in Figs. 1 and 2, dur-
ing the initial 5 min the diffusion of lactose and l-glycine from
bulk solution into the unmodified PVA capsules was the fastest
and diffusion into the modified composite (containing 0.5% (w/v)
DDAB) PVA capsules was the slowest. Moreover, there is a dras-
tic and orderly reduction in the rate of penetration of the test
molecules with increasing concentrations of DDAB. This decreas-
ing trend gradually slowed over time and was close to equilibrium
after 60 min. It can be observed that when compared with the
unmodified PVA capsules, the modified composite PVA capsules
were hydrophobic in the aqueous system. In water–isopropanol
systems, the MONT–DDAB fillers can greatly improve the diffusion
capability of benzyl benzoate from bulk solution into PVA capsules
with low DDAB content (0.05% and 0.1%, w/v) when compared
with unfilled PVA capsules. Surprisingly, the diffusion capability
was sharply decreased when the DDAB content was increased up
to 0.3% (w/v) and beyond (Fig. 3). The combination of these results
indicates that small amounts of cationic surfactants bind to the clay
mineral. The interface of the clay mineral becomes more hydropho-
bic and binding of the PVA to the clay mineral is strengthened.
The materials become amphiphilic as a result of their architecture,
i.e., the chemical constitution resulting from the balance between
hydrophilic and hydrophobic segments or groups in the MONT and
DDAB modified composite PVA capsules, which may provide a more
conducive environment for the desired reaction. With the increas-
ing concentration of the surfactant in the modified composite PVA
capsules, the surfactant molecules bind to PVA and PVA becomes
hydrophilic. These results are in strong agreement with previous
results [13,17]. Therefore, in a water organic two-phase system
(water–isopropanol system), the modified composite PVA capsules
2.8. Reusability
To characterize the reusability of the immobilized cells, appropriate amounts
of the capsule-immobilized cells with modified composite PVA or free cells were
added to the reaction system as described above. The biocatalyst was harvested
after the reaction and washed with 50 mM phosphate buffer, pH 7.5; this process was
repeated 20 times. After each cycle, the ADH activities of the immobilized and free
cells were determined. The residual ADH activity (relative activity) was calculated
as a percentage of its initial activity.
2.9. Storage stability
The capsule-immobilized cells with modified composite PVA and free cells were
stored in 50 mM Na2HPO4/KH2PO4 buffer, pH 7.5 at 4 ◦C. The storage stability was
evaluated by determining the ADH activity at regular time intervals up to 1 month.
The residual ADH activity (relative activity) was calculated as a percentage of its
initial activity.
2.10. Analytical methods
2.10.1. Concentration analysis of hydrophilic and hydrophobic molecules
The concentration of lactose was determined by the colorimetric method (UV-
7504, XinMao) of dinitrosalicylic acid (DNS) [19]. The absorbance was measured
at 515 nm after cooling to room temperature. The concentration of l-glycine was
measured by the ninhydrin method [20] using UV at 570 nm. The concentration of
benzyl benzoate, which was diluted in 95% ethanol, was tested by UV at 260 nm. All
data were presented as the mean values of triplicate experiments.
2.10.2. Enzyme assay
The following method was developed to prepare samples for the determination
of the intracellular levels of ADH activity in the immobilized yeast cells. Approxi-
mately 100 mg of immobilized cell capsules were thoroughly chopped with a sharp

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G.-H. Gong et al. / Process Biochemistry 45 (2010) 1445–1449
Fig. 6. Reaction time course of the bioconversion of COBE to (S)-CHBE by immobi-
lized cells. The ee ( ) and yield ( ) of modified composite PVA capsules and the
ee ( ) and yield (ꢀ) of unmodified PVA capsules.
Fig. 4. Effect of pH on the relative ADH activity of free (ꢀ) and immobilized (
cells.
)
containing 0.05% (w/v) DDAB are the most appropriate choice for
the diffusion of hydrophilic and hydrophobic molecules.
PVA capsules or modified composite PVA capsules as the biocat-
alyst in an organic solvent–water biphasic reaction system at pH
7.5 and 30 ◦C with continuous shaking at 125 rpm, the latter gave
much higher yield of (S)-CHBE than former after reaction for 8 h
(88% versus 74%). Additionally, the product ee was higher when
the reaction was performed with modified composite PVA capsules
(99.1% versus 98.2%). These results suggests faster diffusion of sub-
strate from bulk solution into the modified composite PVA capsules
and more interaction with the intracellular ADH in the immobilized
cells compared to that in unmodified PVA capsules. This finding is
consistent with the results shown in Figs. 1–3.
3.2. Effects of pH and temperature on intracellular ADH activity
The results on the effect of pH on the ADH activity of free and
immobilized cells are given in Fig. 4. The relative ADH activities
of both cells showed obvious differences in pH dependence. The
maximum ADH activity of free cells was observed at pH 8.0 and
of immobilized cells was observed at pH 7.0–8.0. Furthermore,
the retained relative ADH activity of the immobilized cells was
higher both at lower and higher pH in comparison to that of the
free cells. The results indicate that immobilization methods pre-
served the intracellular ADH activity over a wider pH range. The
results on the effect of temperature on the ADH activity of free and
immobilized cells are shown in Fig. 5. The free and immobilized
cells exhibited similar temperature profiles and the maximum ADH
activity of both cells was observed at 30 ◦C. At higher temperatures,
however, immobilized cells were more active than the free cells.
The immobilized cells showed essentially the same ADH activi-
ties over the range of 30–40 ◦C and started to sharply decline at
45 ◦C.
3.4. Reusability
The stability of a catalyst is an important feature for its poten-
tial application in industry. As shown in Fig. 7, the immobilized
cells retained over 88% of their initial ADH activity after 20 cycles.
However, the ADH activity of free cells decreased significantly and
there was almost no activity after six cycles. This result is similar to
the data in the literature [3]. The results indicated that the immobi-
lized cells in the modified composite PVA capsules displayed good
reusability.
3.3. Bioconversion of COBE to (S)-CHBE with
capsule-immobilized cells as a biocatalyst
3.5. Storage stability
Storage stability of a catalyst is also very important for industrial
applications. Time courses of the retained activities of immobilized
and free cells after a long period of storage at 4 ◦C are presented
in Fig. 8. The experimental results indicate that the ADH activ-
ity of immobilized cells decreased more slowly than that of free
The bioreduction of COBE to give the corresponding product (S)-
CHBE is a very interesting reaction because the product is known
to be a key intermediate in the synthesis of inhibitors of HMG-
CoA reductase [22]. As shown in Fig. 6, when using unmodified
Fig. 5. Effect of temperature on the relative ADH activity of free (ꢀ) and immobilized
Fig. 7. Effect of reusability on the relative ADH activity of free (ꢀ) and immobilized
(
) cells.
(
) cells.

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1449
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A new approach for the immobilization of permeabilized
brewer’s yeast cells in modified composite PVA capsules was pre-
sented. An attractive feature of this method is that it is readily
available and very easy to handle. More importantly, it showed
significant advantages over the use of unmodified PVA gel with
regard to the diffusion capabilities of hydrophobic molecules.
Therefore, it may provide a more conducive environment for the
desired reaction. Additionally, the permeabilized brewer’s yeast
cells immobilized in new modified composite PVA capsules not
only exhibited good storage stability and reusability, but also could
be successfully employed for the bioreduction of COBE to (S)-CHBE
with high optical purity. The combination of these results indi-
cates that the immobilization of permeabilized brewer’s yeast cells
into modified composite PVA capsules would probably be a more
promising strategy for the synthesis of (S)-configured chiral alco-
hols.
Acknowledgements
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This work was supported by the special funding of three items
of expenditure in the Science and Technology Department of the
Central District in Chongqing. We also thank the Chongqing Medical
University for partial financial support of this work.
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