lipase catalyst biodiesel
TRANSCRIPT
Investigation of lipases from various Carica papaya varieties
for hydrolysis of olive oil and kinetic resolution of
(R,S)-profen 2,2,2-trifluoroethyl thioesters
I-Son Ng a, Shau-Wei Tsai b,*aDepartment of Chemical Engineering, National Cheng Kung University, Tainan 70101, Taiwan
b Institute of Biochemical and Biomedical Engineering, Chang Gung University, Kwei-Shan Tao-Yuan 33302, Taiwan
Received 17 May 2005; received in revised form 28 September 2005; accepted 6 October 2005
Abstract
With olive oil hydrolysis in aqueous solutions and hydrolytic resolution of (R,S)-profen 2,2,2-trifluoroethyl thioesters in water-saturated
isooctane as the model systems, the lipolysis and enantioselective hydrolysis activities of four partially purified Carica papaya lipases of different
plant variety and geography location of cultures were compared to select pCPL-Indo from Indonesia as the best lipase preparation. For lipolysis, an
optimal pH of 8.5 for all lipase preparations was found. Yet, pCPL-Indo possessed the highest activity at pH ranged from 7 to 10. For the kinetic
resolution, the thermodynamic analysis implied that pCPL-Indo has changed the conformation at 60 8C and the enantiomer discrimination was
dominated by DDH. The kinetic analysis also indicated that the enantiomeric discrimination was mainly due to the difference of k2S and k2R in the
acylation step. Agreements between experimental time-course conversions XS and best-fitted results were illustrated by considering effects of
product inhibition and enzyme deactivation.
# 2005 Elsevier Ltd. All rights reserved.
Keywords: Carica papaya lipases; Lipolysis; Hydrolytic resolution; (R,S)-Profen 2,2,2-trifluoroethyl thioesters
www.elsevier.com/locate/procbio
Process Biochemistry 41 (2006) 540–546
1. Introduction
Lipases (triacylglycerol hydrolases, EC 3.1.1.3) have been
widely applied as versatile biocatalysts for the lipids conversion
and kinetic resolution of a variety of racemates [1–2]. Although
industrial lipases are produced mainly from animals or
microorganisms, Carica papaya lipase stored in the crude
papain and produced from C. papaya latex is now available in
large quantities such that an extensive use in pilot or large-scale
application for lipids bioconversion is possible [3–4].
Recently, we discovered that a crude papain referred as the
crude C. papaya lipase (CPL), as a product from Sri Lanka,
possessed high enantioselectivity for the kinetic resolution of
(R,S)-naproxen 2,2,2-trifluoroethyl thioester and ester in water-
saturated organic solvents, giving the desired (S)-naproxen as
an important non-steroidal anti-inflammatory drug [5–6]. As
the lipase activity is located in the non-water-soluble aggregate
of papaya latex, improvements of enzyme activity, stereo-
* Corresponding author. Tel.: +886 3 2118800x3415; fax: +886 3 2118668.
E-mail address: [email protected] (S.-W. Tsai).
1359-5113/$ – see front matter # 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.procbio.2005.10.011
selectivity and thermal stability were furthermore reported
when CPL was partially purified in deionized water to remove
the water-soluble contaminants [7,8]. Since CPL may be
regarded as a waste in producing the refined papain and
chymopapain from crude papain, the cheap raw material and
low production cost is obviously beneficial for the industrial
application of pCPL as an efficient biocatalyst.
The plant variety, the geography location of cultures and
even different processing conditions from various sources may
affect the biocatalytic activities ofC. papaya lipase stored in the
crude papain. In this work, we compared the lipolysis and
enantioselective hydrolysis activities of pCPL with other
lipases prepared from commercially available and freshly
collected crude preparations of papain. These investigations
were performed in order to have a better chemical character-
ization of these enzymes, to determine the relationship between
the different catalytic activities of partially purified lipases, and
to select the best preparation for lipolysis and kinetic resolution
of racemates.
The hydrolysis of olive oil in aqueous solutions by the pH-
stat method was first employed for comparing the lipolysis
activity. The kinetic resolution of several 2,2,2-trifluoroethyl
I.-S. Ng, S.-W. Tsai / Process Biochemistry 41 (2006) 540–546 541
Nomenclature
eep enantiomeric excess for (S)-naproxen, (XS � XR)/
(XS + XR)
E enantiomeric ratio, i.e. the ratio of initial rates for
both substrates or as k2SKMR/k2RKMS
(Et) lipase concentration (mg/mL)
kd deactivation constant (h�1)
KMR, KMS Michaelis–Menten constants for (R)- and (S)-
thioester (mM)
K2R, K2S kinetic constant for (R)- and (S)-thioester
(mmol/(g h))
KP inhibition constant for (S)-naproxen (mM)
pCPL partially purified Carica papaya lipase from Sri
Lanka
pCPL-China partially purified Carica papaya lipase from
China
pCPL-Indo partially purified Carica papaya lipase from
Indonesia
pCPL-Taiwan partially purified Carica papaya lipase
from Taiwan
(PS) (S)-naproxen concentration (mM)
(SR), (SS) (R)- and (S)-thioester concentration (mM)
(SR)o, (SS)o initial (R)- and (S)-thioester concentration
(mM)
T temperature (K)
VR, VS initial rates of (R)- and (S)-substrates (mM/h)
XR, XS conversions of (R)- and (S)-thioester, i.e.
[1 � (SR)/(SR)o] and [1 � (SS)/(SS)o], respectively
DDG difference in activation free energy between
transient states of (S)- and (R)-thioesters (kJ/mol)
DDH difference in activation enthalpy between tran-
sient states of (S)- and (R)-thioesters (kJ/mol)
DDS difference in activation entropy between the tran-
sient states of (S)- and (R)-thioesters (J/(mol K))
thioesters of (R,S)-2-arylpropionic acids (i.e. (R,S)-profens) in
water-saturated isooctane at different temperature was then
investigated (Scheme 1). Finally, the thermodynamic and
kinetic analysis by considering product inhibition and enzyme
deactivation was carried out to simulate the time-course
conversions of (S)-naproxen thioester.
2. Materials and methods
2.1. Materials
(S)-Naproxen ((S)-2-(6-methoxyl-2-naphthyl)propionic acid), (R,S)-feno-
profen ((R,S)-2-(3-phenoylphenyl)propionic acid) calcium salt, (R,S)-ketopro-
fen ((R,S)-2-(3-benzoylphenyl)propionic acid), (S)- and (R,S)-ibuprofen ((R,S)-
4-isobutyl-2-methylphenylacetic acid), (R,S)-flurbiprofen ((R,S)-2-fluoro-2-
methyl-4-biphenylacetic acid), crude papain (product code P3375, a cystine
protease of 2.1 units/mg, product from Sri Lanka) and phenyl dichloropho-
sphatewere purchased from Sigma (St. Louis,MO). Other crude preparations of
papain were kindly donated from Biacsoft Technologies (Surabaya, Indonesia)
and Javely Biological Products (Nanning, China). We also prepared fresh crude
papain by first tapping green fruits of female papaya planted in the campus,
collecting exuded latex and then lyophilized. Other chemicals of analytical
grade were commercially available as follows: 2,2,2-trifluoroethanethiol from
Aldrich (Milwaukee, WI); isooctane, sodium chloride, chloroform and 1,2-
dimethoxyethane from Tedia (Fairfield, OH); anhydrous pyridine from Riedel-
deHaen (Seelze, Germany). All (R,S)-profen 2,2,2-trifluoroethyl thioesters were
synthesized and characterized according to reference [7].
2.2. Preparation of partially purified papaya lipases
To 1.35 g of the crude papain from different varieties was added 15 mL
deionized water at 4 8C with gentle stirring for 30 min. The resultant solution
was centrifuged to remove the supernatant. The above procedures were repeated
once more. The remaining precipitate was then collected and lyophilized at
�40 8C and 100 mmHg for 4 h, giving about 15% (w/w) recovery based on the
initial crude preparation. Notations pCPL, pCPL-China, pCPL-Indo and pCPL-
Taiwan were referred as the partially purified lipases prepared from the crude
papain produced in Sri Lanka, China, Indonesia and Taiwan, respectively.
2.3. Analysis
The pH-stat method in a Mettler DL-25 titrator (Mettler-Toledo, Switzer-
land) was employed for measuring lipase activity in aqueous solution. The
substrate solution was prepared by stirring 20 mL olive oil and 10 g gum arabic
in 200 mL deionized water. To 15 mL of the substrate solution incubated at
40 8Cwas added 1 mL deionized water containing 5 mg of the partially purified
papaya lipase. The pH of the resultant solution was adjusted from 7 to 10 by
using phosphate buffers and then titrated by using 82 mM NaOH solution. One
unit (U) of the lipase activity was defined as the amount of enzyme required to
release 1 mmol fatty acid/min under the defined assay condition. The back-
ground hydrolysis experiment without adding the lipase at the specific reaction
condition was carried out and deducted from that with the enzyme. Similar
measurements were carried out at pH 8.5 in the temperature ranging from 35 to
60 8C.More experiments for studying enzyme thermal stability were performed
by storing the enzyme solution in a specified temperature for 2 h and then
measured the lipase activity at pH 8.5 and 40 8C.The hydrolysis of (R,S)-profen thioesters in water-saturated organic solvents
were monitored by using HPLC equipped with a chiral column (Chiralcel OD,
Daicel Chemical Industries, Japan) capable of separating the internal standard
of 2-nitrotoluene, (R)- and (S)-thioesters, (R)- and (S)-profens. The mobile
phase was a mixture of n-hexane, isopropanol and acetic acid at a flow rate of
1 mL/min. UV detection at 270 nm was used for quantification at the column
temperature of 25 8C. Detailed analytic conditions for each enantiomer were
given in Table S1 of the Supporting Materials in reference [7].
2.4. Kinetic resolution of (R,S)-profen 2,2,2-trifluoroethyl thioesters
To 135 mg of each lipase preparation was added 10 mL water-saturated
isooctane containing 1 mM (R,S)-naproxen 2,2,2-trifluoroethyl thioester at a
specified temperature. The resultant solution was stirred with a magnetic stirrer.
Sampleswere removed and injectedonto the aboveHPLCsystemat different time
intervals for analysis. From the time-course conversions, the initial rate for each
enantiomer and hence the enantiomeric ratio (i.e. E value defined as the ratio of
initial rates for both substrates) canbeestimated.Similar experimentswerecarried
out by using other (R,S)-profen 2,2,2-trifluoroethyl thioesters as the substrate.
More experiments were performed at 45 and 60 8C for 10 mL water-
saturated isooctane containing 135 mg pCPL (or pCPL-Indo) and (R,S)-
naproxen 2,2,2-trifluoroethyl thioester of concentrations varied from 0.5 to
16.0 mM. The kinetic constants for each enantiomer can be estimated from the
variation of initial rate with initial substrate concentration. Similar experiments
were carried out at 60 8C for studying the product inhibition, where 1 mM (R,S)-
naproxen 2,2,2-trifluoroethyl thioester and (S)-naproxen of concentrations
varied from 0.25 to 1.0 mM were employed.
3. Model development
As the hydrolysis product 2,2,2-trifluoroethanethiol of low
boiling point is a good leaving group, an irreversibleMichaelis–
I.-S. Ng, S.-W. Tsai / Process Biochemistry 41 (2006) 540–546542
Scheme 1.
Fig. 1. Effects of pH on lipase specific activity for the hydrolysis of olive oil in
aqueous solution at 40 8C for: pCPL-Indo (*), pCPL (*), pCPL-China (!)
and pCPL-Taiwan (5).
Menten kinetics can be employed for modeling the lipase-
catalyzed hydrolysis of (R,S)-naproxen 2,2,2-trifluoroethyl
thioester in water-saturated isooctane. By furthermore assum-
ing that (S)-naproxen acts as an inhibitor, the rate equations for
both enantiomers are expressed as
VS ¼�dðSSÞ
dt¼ K2SðSSÞðEtÞ=KMS
1þ ðSSÞ=KMS þ ðSRÞ=KMR þ ðPSÞ=KP
(1)
VR ¼ �dðSRÞdt
¼ k2RðSRÞðEtÞ=KMR
1þ ðSSÞ=KMS þ ðSRÞ=KMR þ ðPSÞ=KP
(2)
Notations (Et), (PS), (SR) and (SS) denote the concentrations of
enzyme, (S)-naproxen, (R)- and (S)-thioester, respectively.
Moreover, k2R, KMR, k2S, KMS and KP are the kinetic constants
in Michaelis–Menten kinetics and inhibition constant, respec-
tively. Since both pCPL and pCPL-Indo are highly enantiose-
lective for the (S)-thioester, one may neglect (SS)/KMS in
Eq. (2), but not in Eq. (1), when estimating k2R and KMR.
By assuming an irreversible first-order deactivation for the
lipase, (PS) = [(SS)o � (SS)] and (SR) = (SS)o in Eq. (1) due to
the high enzyme enantioselectivity, an analytical solution for
(S)-thioester conversion XS derived from Eq. (1) is expressed as
�1þ ðSSÞo
KP½1þ ðSSÞo=KMR�
�ln½1� XA�
þ�
ðSSÞoXS
KP½1þ ðSSÞo=KMR�
�
¼ k2AðEtÞo½exp½�kdt� � 1�kdKMS½1þ ðSSÞo=KMR�
(3)
Therefore, the deactivation constant kd can be estimated from
Eq. (3) and the experimental time-course data of XS.
4. Results and discussion
4.1. Comparison of lipolysis
Fig. 1 illustrated the bell shape of lipase specific activity
varied with pH at 40 8C by using olive oil as the substrate,
where the maximum activity at pH 8.5 for each enzyme
preparation was obtained. Similar result of optimal lipase
activity at pH 8.0 and 55 8C with tributyrin as the substrate has
been reported when using the particulate fraction of crude
papain as the biocatalyst [9]. The highest specific activity of
40.9 U/mg for pCPL-Indo in comparison with 26.7 U/mg for
pCPL, 12.0 U/mg for pCPL-China and 9.1 U/mg for pCPL-
Taiwan was estimated from Fig. 1. Change of pH to 10 or 7.0
I.-S. Ng, S.-W. Tsai / Process Biochemistry 41 (2006) 540–546 543
Fig. 2. (A) Specific activity and (B) residual activity varied with temperature
for the hydrolysis of olive oil in aqueous solution at pH 8.5: for pCPL-Indo (*)
and pCPL(*).
Table 2
Effect of lipase varieties and temperature on E value for hydrolysis of 1 mM
(R,S)-profen 2,2,2-trifluoroethyl thioesters
Lipases (8C) Naproxen Fenoprofen Ketoprofen Flurbiprofen Ibuprofen
pCPL (45) 173 25 30 18 14
pCPL-Indo
(45)
>200 28 23 12 8
pCPL (60) 67 45 20 12 8
pCPL-Indo (65) 158 19 9 8 n.d.
Conditions: 13.5 mg/mL lipase in water-saturated isooctane; n.d. as ‘‘not
determined’’.
resulted in the sharp reduction of specific activity for pCPL-
Indo and pCPL but not for pCPL-China and pCPL-Taiwan. This
implied that C. papaya lipases of different sources may have
different enzyme conformations and hence ionization states at a
specified pH. Indeed, the curve of lipolytic activity shown in
Fig. 1 differed substantially depending on the plant variety and
geography location of cultures. Yet, pCPL-Indo always
maintained the highest activity at pH ranged from 7 to 10.
The specific activity varied with temperature at pH 8.5 was
demonstrated in Fig. 2(A) where a maximum occurred between
40 and 45 8C for pCPL-Indo and 45 to 50 8C for pCPL. Similar
results of 50 8C at pH 8.5 for CPL and 55 8C at pH 8.0 for the
particulate fraction of crude papain were reported when
employing tributyrin as the substrate [9,10]. Fig. 2(B) demon-
strated the enzyme thermal stability at pH 8.5. In general, pCPL-
Indo was more thermally stable than pCPL, yet similar residual
activities around20%for both lipaseswere shownas temperature
was greater than50 8C.Basedon thehigh specific activity, pCPL-Indo was selected as the best lipase for the lipolysis of olive oil.
4.2. Comparison of kinetic resolution
With the hydrolytic resolution of (R,S)-naproxen 2,2,2-
trifluoroethyl thioesters in water-saturated isooctane as the
model system, Table 1 indicated that pCPL was the most active
Table 1
Comparison of specific initial rates, E value, conversions and eep for various lipas
Lipases VS/(Et) � 104 (mmol/(g h)) VR/(Et) � 106 (mmol/(g h
pCPL 9.11 5.26
pCPL-Taiwan 5.74 9.04
pCPL-Indo 4.35 0.67
pCPL-China 0.73 0.75
Conditions: hydrolysis of 1 mM of (R,S)-naproxen 2,2,2-trifluoroethyl thioester by
in obtaining the highest conversion XS at 45 8C. No correlation
between the lipolytic activity for olive oil and hydrolytic
activity for (S)-naproxen thioester was observed. Similarly, no
relationship between the proteolytic and lipolytic activities for
the crude papaya latex from different plant variety has been
found [10]. However, all lipase preparations possessed good to
excellent enantioselectivity, with pCPL-Indo to be the most
enantioselective.
Increase of temperature to 60 8C resulted in an enhancement
of pCPL activity for (R)- and (S)-naproxen 2,2,2-trifluoroethyl
thioester (Fig. 3(A and B)), yet with the reduction of E value
from 173 to 67 (Table 2). Similarly, the E value decreased from
650 (or >200) to 183 (or 158) for pCPL-Indo when increasing
the temperature from 45 to 60 8C (or 65 8C). It stressed that in
comparison with pCPL-Indo, pCPL possessed higher initial
rate for (S)-naproxen 2,2,2-trifluoroethyl thioester at 45 8C(Fig. 4(A)), but opposite at 60 8C (Fig. 4(B)). This implied that
pCPL-Indo might have changed the conformation at 60 8C,which was elucidated latter.
By changing the substrate to other (R,S)-profen 2,2,2-
trifluoroethyl thioesters, pCPL-Indo in general showed lower
activity for the (S)-substrate compared with pCPL at 45 8C(Fig. 3(A)), but opposite at higher temperature (Fig. 3(B)). Yet
except for (R,S)-fenoprofen 2,2,2-trifluoroethyl thioester, both
lipases possessed similar E values for a specific racemic
substrate when temperature increased. In order to elucidate this
interesting behavior, the thermodynamic and kinetic analysis in
water-saturated isooctane containing (R,S)-naproxen 2,2,2-
trifluoroethyl thioester for both lipases was performed.
4.3. Thermodynamic analysis
The thermodynamic analysis has been proposed to
investigate effects of solvent type and mixture, acyl donor
and acceptor, lipase type and mutant on the temperature
dependence of E value in lipase-catalyzed kinetic resolutions
e varieties
)) E Time (h) XS (%) XR (%) eep (%)
173 120 88.5 2.52 94.5
64 126 65.6 3.43 90.1
>200 124 66.8 0.24 99.3
97 124 10.0 0.25 95.1
using 13.5 mg/mL lipase in water-saturated isooctane at 45 8C.
I.-S. Ng, S.-W. Tsai / Process Biochemistry 41 (2006) 540–546544
Fig. 3. Initial rates of fast-reacting enantiomer of various (R,S)-profen 2,2,2-
trifluoroethyl thioesters: (A) for pCPL-Indo (empty bar) and pCPL (filled bar) at
45 8C and (B) for pCPL-Indo (empty bar) at 65 8C and pCPL (filled bar) at
60 8C. Notations: Nap, Feno, Keto, Flu and Ibu represent 2,2,2-trifluoroethyl
thioesters of (R,S)-naproxen, (R,S)-fenoprofen, (R,S)-ketoprofen, (R,S)-flurbi-
profen and (R,S)-ibuprofen, respectively.
Fig. 4. (A) Variations of initial ln(VR) (! and 5) and ln(VS) (* and *) with
inverse of absolute temperature for pCPL-Indo (empty) and pCPL (filled). (B)
Variation of ln(E) with inverse of absolute temperature for pCPL-Indo (*) and
pCPL (*). Condition: hydrolytic resolution of 1 mM (R,S)-naproxen 2,2,2-
trifluoroethyl thioester in water-saturated isooctane.
[2,11–15]. The difference in activation free energy DDG for the
transient states of fast-reacting enantiomer, i.e. (S)-naproxen,
(S)-flurbiprofen, (S)-ibuprofen, (R)-fenoprofen or (R)-ketopro-
fen thioester, and slow-reacting enantiomer, i.e. (R)-naproxen,
(R)-flurbiprofen, (R)-ibuprofen, (S)-fenoprofen or (S)-ketopro-
fen thioester, can be separated into the differences in activation
Table 3
Kinetic constants for hydrolytic resolution of (R,S)-naproxen 2,2,2-trifluoroethyl th
Lipase (8C) k2S � 103 (mmol/(g h)) k2R � 104 (mmol/(g h))
pCPL (45) 6.33 3.20
pCPL-Indo (45) 2.75 0.07
pCPL (60) 16.79 3.00
pCPL-Indo (60) 47.21 4.00
enthalpy (DDH) and activation entropy (DDS). Therefore, a
clear elucidation on whether the enantiomer discrimination to
be either enthalpy-driven or entropy-driven or both equally
important is reached.
The variations of logarithm of initial rates versus the inverse
of absolute temperature for pCPL and pCPL-Indo were
ioester in water-saturated isooctane at 45 and 60 8C for pCPL-Indo and pCPL
KMS (mM) KMR (mM) KP (mM) kd � 102 (h�1)
2.68 19.9 0.80 0.43
1.43 2.77 0.50 0.39
5.72 6.67 1.53 0.69
3.66 6.74 1.66 2.68
I.-S. Ng, S.-W. Tsai / Process Biochemistry 41 (2006) 540–546 545
Fig. 5. (A) Variation of initial V�1S with (PS) and (B) variations of initial VR (&)
and VS (5) with initial substrate concentration with (SR)o or (SS)o at 60 8C for
pCPL-Indo. (—) Best-fitted results.
Fig. 6. Time-course conversions of XS: for pCPL-Indo at 60 8C (5), pCPL at
60 8C (!), pCPL-Indo at 45 8C (*) and pCPL at 45 8C (*). (—) Best-fitted
results.
illustrated in Fig. 4(A). The Arrhenius relationship for either
(R)- or (S)-thioester was observed, implying that pCPL was still
stable at 80 8C. These behaviors were valid for pCPL-Indo, yetan obvious change of the slope of Arrhenius relationship at
60 8C was illustrated. This implied that pCPL-Indo might have
changed the conformation, yet more experiments to confirm
this deduction by using purified papaya lipases as the
biocatalyst were needed.
Inspections of Fig. 4(B) revealed that pCPL-Indo was more
enantioselective, which was mainly due to the lower initial VR
at temperature less than 60 8C and the higher VS at the higher
temperature. The relationship RT ln(E) = �DDH + T DDS was
employed to estimate DDH and DDS from Fig. 4(B) for both
lipases. The results for pCPL were DDH = �41.75 kJ/mol and
DDS = �89.12 J/(mol K), and those for pCPL-Indo as
DDH = �73.52 kJ/mol and DDS = �177.2 J/(mol K) at tem-
perature ranged from 45 to 60 8C as well as DDH = �41.63 kJ/
mol and DDS = �81.02 J/(mol K) at temperature ranged from
60 to 80 8C, respectively. The large difference of activation
enthalpy between the transient states of both enantiomers at
these two temperature ranges implied that the enzyme
conformation for pCPL-Indo did change at 60 8C.A good linear relationship of DDS = 26.87 + 2.951 DDH
(r2 = 0.979) has been reported previously, no matter what
combination of lipase sources, solvents, hydrolysis for (R,S)-
profen 2,2,2-trifluoroethyl ester and thioester or esterification
for (R,S)-naproxen and 2-(4-chloro-phenoxy)propionic acid
was made [16]. This linear enthalpy–entropy compensation
relationship was modified as DDS = 26.85 + 3.028 DDH
(r2 = 0.981) when data for pCPL-Indo were added. From the
variation of DDH and DDS for pCPL-Indo and pCPL, it
concluded that both activation enthalpy and activation entropy
were important for the enantiomer discrimination, yet the
former was dominating in the temperature range investigated.
4.4. Kinetic analysis
Fig. 5(A and B) illustrated the initial V�1S varied with (PS)
and initial rates changed with the substrate concentration,
respectively, for pCPL-Indo at 60 8C and other conditions (not
given here). The kinetic constants were then estimated form
Eqs. (1) and (2), and represented in Table 3. In general, the
enzyme enantioselectivity for both lipases was mainly due to
the difference of k2S and k2R, i.e. the formation and breaking of
transient states for both substrates in the acylation step. In
comparison with pCPL, the lower initial rate VS for pCPL-Indo
at 45 8C and vice versa at higher temperature (Fig. 4(A)) was
attributed to the great enhancement of k2S. Moreover, by
comparing KP and KMS, each lipase preparation possessed
higher affinity for (S)-naproxen in comparison with (S)-
naproxen thioester.
The enzyme deactivation constants represented in Table 3
for both lipases at different temperature were furthermore
estimated from the time-course conversions XS and Eq. (3).
Agreements between the time-course conversions XS and best-
fitted results were illustrated in Fig. 6.
5. Conclusions
With olive oil hydrolysis in aqueous solutions as the
model system, the lipolysis activities for four partially
purified lipases prepared from the crude papain of various
varieties were first compared. An optimal pH of 8.5 at 40 8Cfor all lipase preparations was found, yet pCPL-Indo from
Indonesia possessed the highest specific activity at pH ranged
from 7 to 10. Maximum enzyme activities between 40 and
45 8C for pCPL-Indo and between 45 and 50 8C for pCPL
from Sri Lanka were obtained. Moreover, the former
demonstrated better enzyme thermal stability as temperature
I.-S. Ng, S.-W. Tsai / Process Biochemistry 41 (2006) 540–546546
was less than 50 8C and vice versa at temperature greater than
50 8C.With the hydrolytic resolution of (R,S)-naproxen 2,2,2-
trifluoroethyl thioester in water-saturated isooctane as the
model system, pCPL and pCPL-Indo possessed the highest
lipase activity and enantioselectivity for the (S)-thioester at
45 8C, respectively. Yet, pCPL-Indo was superior to pCPL at
the temperature greater than 55 8C. Very similar performances
for both lipase preparations were found when other (R,S)-
profen 2,2,2-trifluoroethyl thioesters were used as substrates.
The thermodynamic analysis indicated that the enantiomer
discrimination was driven byDDH and DDS, yet the former was
dominating for both lipase preparations. From the variation of
DDH with temperature, pCPL-Indo might change the con-
formation at 60 8C.The kinetic analysis for pCPL and pCPL-Indo indicated that
the enantiomeric discrimination was mainly due to the
difference of k2S and k2R in the acylation step. Moreover, k2Sbut not KMS possessed more influence on the initial rate VS
when comparing the lipase activity at different temperature and
lipase preparation. Agreements between the time-course
conversions XS and best-fitted results for pCPL-Indo were
obtained when the product inhibition and enzyme deactivation
were considered. Based on the enzyme performance of activity
and enantioselectivity, pCPL-Indo was selected as the best
lipase preparation.
Acknowledgement
The financial support of NSC 93-2214-E-006-008 from
National Science Council is appreciated.
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