1
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P. Speranza et al. / Journal of Molecular Catalysis B: Enzymatic 72 (2011) 181–186
2.2. Microorganism preservation and preparation of the
percentage residual activities were calculated by comparison to
pre-inoculums
untreated control enzyme. All the above tests were carried out in
duplicate.
A F. oxysporum strain isolated from soil and plants was selected
in a previous study with 400 strains of fungi as the best cutinase
producer. The culture medium used for this previous selection con-
tained apple cutin as the sole carbon source [5]. The strain was
maintained in potato dextrose Agar (PDA; Acumedia Manufactures
2
.5.3. Effect of metal ions
The effects of CaCl , KCl, HgCl , MnCl , CoCl , K HPO , NaNO ,
2
2
2
2
2
4
3
FeSO , MgSO , ZnSO , MnSO , K SO , Na SO and NaHSO3 on the
4
4
4
4
2
4
2
4
cutinolytic activity were investigated. Final concentrations of each
metal ion in the reaction mixture were 1 mM and 10 mM. The per-
centages of activities were determined by comparison with the
control mixture with no metal ion added. All the above tests were
carried out in duplicate.
◦
Inc. Lansing, MI, USA) slants and stored at 4 C. The pre-inoculum
was prepared by adding 2.5 mL of distilled water to remove the
7
spores, obtaining a suspension containing 7 × 10 spores/mL.
2.3. Cutinase production
2
.5.4. Substrate specificity
The influence of different substrates on the cutinolytic activ-
Three by-products were selected due to cutinase activity in
preliminary experiments and good development of F. oxysporum
strain: wheat bran, soybean rind and rice bran [3]. J. curcas seed
cake was also included in this study, because of its availability.
Brazil is a major producer of oil and the use in biotechnological
process of cake produced after extraction is very advantageous
from the environmental and economic point of views [6]. Crude
enzymes extracts were prepared as previously reported [3]. The
crude cutinases produced in each medium (wheat bran, soybean
rind, rice bran and J. curcas seed cake) were used in all experiments
of the biochemical characterization. The crude cutinases produced
in the mediums with wheat bran and soybean rind were used for
the enantioselective characterization.
ity was investigated replacing the p-NPB of the reaction described
above (cutinase assay) by the following substrates: p-nitrophenyl
caprilate (p-NPC), p-nitrophenyl laurate (p-NPL) and p-nitrophenyl
palmitate (p-NPP). All the above tests were carried out in duplicate.
2.5.5. Stability in organic solvent
The stability of the crude cutinases in acetone, methanol,
ethanol, butanol, propanol, hexane and octanol was tested. The
mixture of crude cutinases and 1 mL of each organic solvent
given above was incubated for 1 h at optimum temperature of the
enzymes. After this the organic solvents were dried with N and the
2
activities were determined by comparison with the control mixture
with no organic solvent added. All the above tests were carried out
in duplicate.
2.4. Cutinase assay
The activity against p-nitrophenyl butyrate (p-NPB) was deter-
2
.6. Esterification of (R) and (S)-2-octanol and enantioselective
mined as previously reported [5]. The hydrolysis of p-NPB
was spectrophotometrically monitored for the formation of p-
nitrophenol at 405 nm.
esterification of (R,S)-2-octanol
The reactions of esterification and enantioselective esterifica-
tion were performed with the crude cutinase produced in mediums
composed by wheat bran and soybean rind, these enzymes were
selected after preliminary tests (thin layer chromatography), that
indicated these enzymes were the most enantioselective (data not
shown).
One unit of cutinase activity was defined as the amount of
enzymes required to convert 1 mol of p-NPB to p-nitrophenol per
minute, under the specified conditions [7].
2
2
.5. Biochemical characteristics of the crude cutinases
.5.1. Effects of temperature and thermal stability
2.6.1. Esterification of (R) and (S)-2-octanol
To determine the optimum temperature for cutinolytic activ-
The esterification of (R) and (S)-2-octanol was performed in a
ity, enzymatic reactions at various temperatures over the range of
◦
mixed reaction containing 40 mM of each enantiomerically pure
of 2-octanol, 40 mM of octanoic or hexanoic acid, 4 mL of hexane
and the crude cutinase of wheat bran and soybean rind. The reac-
2
5–75 C were performed by using the procedure described above
(
cutinase assay).
In order to determine the thermal stability, aliquots of each
◦
tion was carried out at 30 C, 168 h and 130 rpm. Experiments with
crude cutinase in Eppendorf tubes were incubated for 1 h at various
◦
no added enzyme were carried out to evaluate the percentage of
spontaneous esterification in the system. The ester formation was
followed using a Chrompack gas cromatograph (Chrompack Co.,
Holland) equipped with a flame ionization detector and a column
temperatures over 30 C to boiling temperature. After incubation,
the tubes were rapidly cooled in an ice bath and then brought to
room temperature. The activities were determined with the cuti-
nase assay described previously. The percentage residual activities
were calculated by comparison to untreated control enzyme. All
the above tests were carried out in duplicate.
(
i.d. 0.32 mm, length 30 m) CP-WAX 52 CB. The initial temperature
◦
of the column was 50 C for 2 min then the temperature increase
at a rate of 10 C/min up to 220 C. For the analysis, H was used as
the carrier gas and the detector and injector were set at 250 C and
2
◦
◦
2
◦
2.5.2. Effects of pH and pH stability
◦
20 C, respectively.
The effect of pH on cutinolytics activities was determined by
using the following buffers (all at 0.1 mM): acetate buffer pH 3.6,
4
8
.0, 5.0, 5.6; phosphate buffer pH 6.0, 6.5, 7.0; Tris–HCl buffer pH
.0, 8.5, 9.0 and borate–NaOH pH 9.5, 10.0. The activities were
2.6.2. Gas chromatography analysis
The reaction conditions of the resolution of (R,S)-2-octanol was
performed under the same conditions described above (esterifi-
cation of (R) and (S)-2-octanol). The enantiomeric excess (eep) of
the ester produced was determined using Chrompack gas chro-
matograph (Chrompack Co., Holland) equipped with a fused silica
determined with the cutinase assay described previously at opti-
mum temperature of the enzymes.
The same buffers were used to determine pH stability of the
crudes cutinases for cutinolytics activities. The mixture of each
crude cutinases and 1 mL of buffer given above was incubated
for 24 h at optimum temperature of the enzymes. The activities
were determined with the cutinase assay described previously. The
TM
capillary quiral column BETA DEX 120 (0.25 mm, 60 m, Supelco).
◦
The initial temperature of the column was 95 C for 30 min, and
then the temperature increased at a rate of 5 C/min up to 220 C.
◦
◦