共查询到20条相似文献,搜索用时 453 毫秒
1.
Jin Zhou Ju Chu Yong-Hong Wang Si-Liang Zhang Ying-Ping Zhuang Zhong-Yi Yuan 《World journal of microbiology & biotechnology》2008,24(6):789-796
An intracellular S-adenosylmethionine synthetase (SAM-s) was purified from the fermentation broth of Pichia pastoris GS115 by a sequence chromatography column. It was purified to apparent homogeneity by (NH4)2SO4 fractionation (30–60%), anion exchange, hydrophobic interaction, anion exchange and gel filtration chromatography. HPLC showed
the purity of purified SAM-s was 91.2%. The enzyme was purified up to 49.5-fold with a final yield of 20.3%. The molecular
weight of the homogeneous enzyme was 43.6 KDa, as determined by electro-spray ionization mass spectrometry (ESI-MS). Its isoelectric
point was approximately 4.7, indicating an acidic character. The optimum pH and temperature for the enzyme reaction were 8.5
and 35 °C, respectively. The enzyme was stable at pH 7.0–9.0 and was easy to inactivate in acid solution (pH ≤ 5.0). The temperature
stability was up to 45 °C. Metal ions, such as, Mn2+ and K+ at the concentration of 5 mM had a slight activation effect on the enzyme activity and the Mg2+ activated the enzyme significantly. The enzyme activity was strongly inhibited by heavy metal ions (Cu2+ and Ag2+) and EDTA. The purified enzyme from the transformed Pichia pastoris synthesized S-adenosylmethionine (SAM) from ATP and l-methionine in vitro with a K
m of 120 and 330 μM and V
max of 8.1 and 23.2 μmol/mg/min for l-methionine and ATP, respectively. 相似文献
2.
Takashi Nemoto Taisuke Watanabe Yutaka Mizogami Jun-ichi Maruyama Katsuhiko Kitamoto 《Applied microbiology and biotechnology》2009,82(6):1105-1114
The recombinant Pichia pastoris harboring an improved methionine adenosyltransferase (MAT) shuffled gene was employed to biosynthesize S-adenosyl-l-methionine (SAM). Two l-methionine (l-Met) addition strategies were used to supply the precursor: the batch addition strategy (l-Met was added separately at three time points) and the continuous feeding strategies (l-Met was fed continuously at the rate of 0.1, 0.2, and 0.5 g l−1 h−1, respectively). SAM accumulation, l-Met conversion rate, and SAM productivity with the continuous feeding strategies were all improved over the batch addition
strategy, which reached 8.46 ± 0.31 g l−1, 41.7 ± 1.4%, and 0.18 ± 0.01 g l−1 h−1 with the best continuous feeding strategy (0.2 g l−1 h−1), respectively. The bottleneck for SAM production with the low l-Met feeding rate (0.1 g L−1 h−1) was the insufficient l-Met supply. The analysis of the key enzyme activities indicated that the tricarboxylic acid cycle and glycolytic pathway
were reduced with the increasing l-Met feeding rate, which decreased the adenosine triphosphate (ATP) synthesis. The MAT activity also decreased as the l-Met feeding rate rose. The reduced ATP synthesis and MAT activity were probably the reason for the low SAM accumulation when
the l-Met feeding rate reached 0.5 g l−1 h−1. 相似文献
3.
An S-adenosylmethionine synthetase gene (metK) from Streptomyces spectabilis was cloned into an expression plasmid under the control of an inducible T7 promoter and introduced into a strain of Escherichia coli (BAP1(pBP130/pBP144)) capable of producing the polyketide product 6-deoxyerythronolide B (6-dEB). The metK coexpression in BAP1(pBP130/pBP144) improved the specific production of 6-dEB from 10.86 to 20.08 mg l−1
. In an effort to probe the reason for this improvement, a series of gene deletion and expression experiments were conducted
based on a metK metabolic pathway that branches between propionyl-CoA (a 6-dEB precursor) and autoinducer compounds. The deletion and expression
studies suggested that the autoinducer pathway had a larger impact on improved 6-dEB biosynthesis. Supporting these results
were experiments demonstrating the positive effect conditioned media (the suspected location of the autoinducer compounds)
had on 6-dEB production. Taken together, the results of this study show an increase in heterologous 6-dEB production concomitant
with heterologous metK gene expression and suggest that the mechanism for this improvement is linked to native autoinducer compounds. 相似文献
4.
Kenro Tokuhiro Nobuhiro Ishida Eiji Nagamori Satoshi Saitoh Toru Onishi Akihiko Kondo Haruo Takahashi 《Applied microbiology and biotechnology》2009,82(5):883-890
Expression of a heterologous l-lactate dehydrogenase (l-ldh) gene enables production of optically pure l-lactate by yeast Saccharomyces cerevisiae. However, the lactate yields with engineered yeasts are lower than those in the case of lactic acid bacteria because there
is a strong tendency for ethanol to be competitively produced from pyruvate. To decrease the ethanol production and increase
the lactate yield, inactivation of the genes that are involved in ethanol production from pyruvate is necessary. We conducted
double disruption of the pyruvate decarboxylase 1 (PDC1) and alcohol dehydrogenase 1 (ADH1) genes in a S. cerevisiae strain by replacing them with the bovine l-ldh gene. The lactate yield was increased in the pdc1/adh1 double mutant compared with that in the single pdc1 mutant. The specific growth rate of the double mutant was decreased on glucose but not affected on ethanol or acetate compared
with in the control strain. The aeration rate had a strong influence on the production rate and yield of lactate in this strain.
The highest lactate yield of 0.75 g lactate produced per gram of glucose consumed was achieved at a lower aeration rate. 相似文献
5.
The excretion of the aromatic amino acid l-tyrosine was achieved by manipulating three gene targets in the wild-type Escherichia coli K12: The feedback-inhibition-resistant (fbr) derivatives of aroG and tyrA were expressed on a low-copy-number vector, and the TyrR-mediated regulation of the aromatic amino acid biosynthesis was
eliminated by deleting the tyrR gene. The generation of this l-tyrosine producer, strain T1, was based only on the deregulation of the aromatic amino acid biosynthesis pathway, but no
structural genes in the genome were affected. A second tyrosine over-producing strain, E. coli T2, was generated considering the possible limitation of precursor substrates. To enhance the availability of the two precursor
substrates phosphoenolpyruvate and erythrose-4-phosphate, the ppsA and the tktA genes were over-expressed in the strain T1 background, increasing l-tyrosine production by 80% in 50-ml batch cultures. Fed-batch fermentations revealed that l-tyrosine production was tightly correlated with cell growth, exhibiting the maximum productivity at the end of the exponential
growth phase. The final l-tyrosine concentrations were 3.8 g/l for E. coli T1 and 9.7 g/l for E. coli T2 with a yield of l-tyrosine per glucose of 0.037 g/g (T1) and 0.102 g/g (T2), respectively. 相似文献
6.
Production of <Emphasis Type="SmallCaps">l</Emphasis>-alanine by metabolically engineered <Emphasis Type="Italic">Escherichia coli</Emphasis> 总被引:2,自引:0,他引:2
Zhang X Jantama K Moore JC Shanmugam KT Ingram LO 《Applied microbiology and biotechnology》2007,77(2):355-366
Escherichia coli W was genetically engineered to produce l-alanine as the primary fermentation product from sugars by replacing the native d-lactate dehydrogenase of E. coli SZ194 with alanine dehydrogenase from Geobacillus stearothermophilus. As a result, the heterologous alanine dehydrogenase gene was integrated under the regulation of the native d-lactate dehydrogenase (ldhA) promoter. This homologous promoter is growth-regulated and provides high levels of expression during anaerobic fermentation.
Strain XZ111 accumulated alanine as the primary product during glucose fermentation. The methylglyoxal synthase gene (mgsA) was deleted to eliminate low levels of lactate and improve growth, and the catabolic alanine racemase gene (dadX) was deleted to minimize conversion of l-alanine to d-alanine. In these strains, reduced nicotinamide adenine dinucleotide oxidation during alanine biosynthesis is obligately
linked to adenosine triphosphate production and cell growth. This linkage provided a basis for metabolic evolution where selection
for improvements in growth coselected for increased glycolytic flux and alanine production. The resulting strain, XZ132, produced
1,279 mmol alanine from 120 g l−1 glucose within 48 h during batch fermentation in the mineral salts medium. The alanine yield was 95% on a weight basis (g
g−1 glucose) with a chiral purity greater than 99.5% l-alanine.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
Previous work from our laboratory has shown that most of Bacillus thuringiensis strains possess the ability to produce melanin in the presence of l-tyrosine at elevated temperatures (42 °C). Furthermore, it was shown that the melanin produced by B. thuringiensis was synthesized by the action of tyrosinase, which catalyzed the conversion of l-tyrosine, via l-DOPA, to melanin. In this study, the tyrosinase-encoding gene (mel) from B. thuringiensis 4D11 was cloned using PCR techniques and expressed in Escherichia coli DH5 . A DNA fragment with 1179 bp which contained the intact mel gene in the recombinant plasmid pGEM1179 imparted the ability to synthesize melanin to the E. coli recipient strain. The nucleotide sequence of this DNA fragment revealed an open reading frame of 744 bp, encoding a protein of 248 amino acids. The novel mel gene from B.thuringiensis expressed in E. coli DH5 conferred UV protection on the recipient strain. 相似文献
8.
Yoshinori Takagi Teruhide Sugisawa Tatsuo Hoshino 《Applied microbiology and biotechnology》2009,82(6):1049-1056
A single-stage continuous fermentation process for the production of 2-keto-l-gulonic acid (2KGA) from l-sorbose using Ketogulonigenium vulgare DSM 4025 was developed. The chemostat culture with the dilution rate that was calculated based on the relationship between
the 2KGA production rate and the 2KGA concentration was feasible for production with high concentration of 2KGA. In this system,
112.2 g/L of 2KGA on the average was continuously produced from 114 g/L of l-sorbose. A steady state of the fermentation was maintained for the duration of more than 110 h. The dilution rate was kept
in the range of 0.035 and 0.043 h−1, and the 2KGA productivity was 3.90 to 4.80 g/L/h. The average molar conversion yield of 2KGA from l-sorbose was 91.3%. Under the optimal conditions, l-sorbose concentration was kept at 0 g/L. Meanwhile, the dissolved oxygen level was changing in response to the dilution rate
and 2KGA concentration. In the dissolved oxygen (DO) range of 16% to 58%, it was revealed that the relationship between DO
and D possessed high degree of positive correlation under the l-sorbose limiting condition (complete consumption of l-sorbose). Increasing D closer to the critical value for washing out point of the continuous fermentation, DO value tended to be gradually increased
up to 58%. In conclusion, an efficient and reproducible continuous fermentation process for 2KGA production by K. vulgare DSM 4025 could be developed using a medium containing baker’s yeast without using a second helper microorganism. 相似文献
9.
Blombach B Schreiner ME Moch M Oldiges M Eikmanns BJ 《Applied microbiology and biotechnology》2007,76(3):615-623
Intracellular precursor supply is a critical factor for amino acid productivity of Corynebacterium glutamicum. To test for the effect of improved pyruvate availability on l-lysine production, we deleted the aceE gene encoding the E1p enzyme of the pyruvate dehydrogenase complex (PDHC) in the l-lysine-producer C. glutamicum DM1729 and characterised the resulting strain DM1729-BB1 for growth and l-lysine production. Compared to the host strain, C. glutamicum DM1729-BB1 showed no PDHC activity, was acetate auxotrophic and, after complete consumption of the available carbon sources
glucose and acetate, showed a more than 50% lower substrate-specific biomass yield (0.14 vs 0.33 mol C/mol C), an about fourfold
higher biomass-specific l-lysine yield (5.27 vs 1.23 mmol/g cell dry weight) and a more than 40% higher substrate-specific l-lysine yield (0.13 vs 0.09 mol C/mol C). Overexpression of the pyruvate carboxylase or diaminopimelate dehydrogenase genes
in C. glutamicum DM1729-BB1 resulted in a further increase in the biomass-specific l-lysine yield by 6 and 56%, respectively. In addition to l-lysine, significant amounts of pyruvate, l-alanine and l-valine were produced by C. glutamicum DM1729-BB1 and its derivatives, suggesting a surplus of precursor availability and a further potential to improve l-lysine production by engineering the l-lysine biosynthetic pathway.
This study is dedicated to Prof. Dr. Hermann Sahm on the occasion of his 65th birthday. 相似文献
10.
Kawaguchi H Sasaki M Vertès AA Inui M Yukawa H 《Applied microbiology and biotechnology》2008,77(5):1053-1062
Corynebacterium glutamicum was metabolically engineered to broaden its substrate utilization range to include the pentose sugar l-arabinose, a product of the degradation of lignocellulosic biomass. The resultant CRA1 recombinant strain expressed the Escherichia coli genes araA, araB, and araD encoding l-arabinose isomerase, l-ribulokinase, and l-ribulose-5-phosphate 4-epimerase, respectively, under the control of a constitutive promoter. Unlike the wild-type strain,
CRA1 was able to grow on mineral salts medium containing l-arabinose as the sole carbon and energy source. The three cloned genes were expressed to the same levels whether cells were
cultured in the presence of d-glucose or l-arabinose. Under oxygen deprivation and with l-arabinose as the sole carbon and energy source, strain CRA1 carbon flow was redirected to produce up to 40, 37, and 11%,
respectively, of the theoretical yields of succinic, lactic, and acetic acids. Using a sugar mixture containing 5% d-glucose and 1% l-arabinose under oxygen deprivation, CRA1 cells metabolized l-arabinose at a constant rate, resulting in combined organic acids yield based on the amount of sugar mixture consumed after
d-glucose depletion (83%) that was comparable to that before d-glucose depletion (89%). Strain CRA1 is, therefore, able to utilize l-arabinose as a substrate for organic acid production even in the presence of d-glucose. 相似文献
11.
l-arabinose isomerase (EC5.3.1.4. AI) mediates the isomerization of d-galactose into d-tagatose as well as the conversion of l-arabinose into l-ribulose. The AI from Lactobacillus plantarum SK-2 was purified to an apparent homogeneity giving a single band on SDS–PAGE with a molecular mass of 59.6 kDa. Optimum
activity was observed at 50°C and pH 7.0. The enzyme was stable at 50°C for 2 h and held between pH 4.5 and 8.5 for 1 h. AI
activity was stimulated by Mn2+, Fe3+, Fe2+, Ca2+ and inhibited by Cu2+, Ag+, Hg2+, Pb2+. d-galactose and l-arabinose as substrates were isomerized with high activity. l-arabitol was the strongest competitive inhibitor of AI. The apparent Michaelis–Menten constant (K
m), for galactose, was 119 mM. The first ten N-terminal amino acids of the enzyme were determined as MLSVPDYEFW, which is identical to L. plantarum (Q88S84). Using the purified AI, 390 mg tagatose could be converted from 1,000 mg galactose in 96 h, and this production
corresponds to a 39% equilibrium. 相似文献
12.
The rpiB gene, encoding ribose-5-phosphate isomerase (RpiB) from Clostridium thermocellum, was cloned and expressed in Escherichia coli. RpiB converted d-psicose into d-allose but it did not convert d-xylose, l-rhamnose, d-altrose or d-galactose. The production of d-allose by RpiB was maximal at pH 7.5 and 65°C for 30 min. The half-lives of the enzyme at 50°C and 65°C were 96 h and 4.7 h,
respectively. Under stable conditions of pH 7.5 and 50°C, 165 g d-allose l−1
was produced without by-products from 500 g d-psicose l−1 after 6 h. 相似文献
13.
Wenjuan Yao Xiaozhao Deng Hui Zhong Miao Liu Pu Zheng Zhihao Sun Yun Zhang 《Journal of industrial microbiology & biotechnology》2009,36(7):911-921
Corynebacterium glutamicum strains are used for the fermentative production of l-glutamate. Five C. glutamicum deletion mutants were isolated by two rounds of selection for homologous recombination and identified by Southern blot analysis.
The growth, glucose consumption and glutamate production of the mutants were analyzed and compared with the wild-type ATCC
13032 strain. Double disruption of dtsR1 (encoding a subunit of acetyl-CoA carboxylase complex) and pyc (encoding pyruvate carboxylase) caused efficient overproduction of l-glutamate in C. glutamicum; production was much higher than that of the wild-type strain and ΔdtsR1 strain under glutamate-inducing conditions. In the absence of any inducing conditions, the amount of glutamate produced by
the double-deletion strain ΔdtsR1Δpyc was more than that of the mutant ΔdtsR1. The activity of phosphoenolpyruvate carboxylase (PEPC) was found to be higher in the ΔdtsR1Δpyc strain than in the ΔdtsR1 strain and the wild-type strain. Therefore, PEPC appears to be an important anaplerotic enzyme for glutamate synthesis in
ΔdtsR1 derivatives. Moreover, this conclusion was confirmed by overexpression of ppc and pyc in the two double-deletion strains (ΔdtsR1Δppc and ΔdtsR1Δpyc), respectively. Based on the data generated in this investigation, we suggest a new method that will improve glutamate production
strains and provide a better understanding of the interaction(s) between the anaplerotic pathway and fatty acid synthesis. 相似文献
14.
Shahriar Saiedian Ezzatollah Keyhani Jacqueline Keyhani 《Acta Physiologiae Plantarum》2007,29(5):463-471
Crocus sativus L., cultivated since ancient times as the source of saffron, is a triploid plant that can be propagated only via its corms
which undergo a period of dormancy. Understanding the processes taking place in the corm is essential to preserve the plant
and improve its quality. Color and taste being of prime importance in the quality of the saffron spice, knowledge on polyphenol
oxidase (PPO) activity in the plant is of particular interest given the role of the enzyme in fruit and vegetable browning
during processing and during the storage of processed food. In this paper, PPO activity was investigated for the first time
in extracts obtained from dormant C. sativus L. corms. PPO activity was detectable using l-DOPA, pyrogallol, catechol or p-cresol as substrate, each being oxidized to its corresponding o-quinone; no activity was detectable with l-tyrosine, tyramine or phenol as substrate. Two pH optima, respectively at 4.5 and 6.7, were observed with all substrates
and a third one, at 8.5, was found with l-DOPA and p-cresol. Kinetics parameters studied at pH 6.7 indicated the highest catalytic efficiency (in units mg−1 prot mM−1) with pyrogallol: 150, then catechol: 39, l-DOPA: 6.4 and p-cresol: 4.6. The enzymatic activity was inhibited by 50% in the presence of 0.22, 0.35, 0.5 and 0.7 mM kojic acid with, respectively,
catechol, pyrogallol, p-cresol and l-DOPA as substrate. When stained for PPO activity, non-denaturing gel electropherograms of extract revealed three distinct
bands, indicating the presence of multiple isoenzymes in dormant C. sativus L. corms. 相似文献
15.
Wu S Yu Z Wang F Li W Ye C Li J Tang J Ding J Zhao J Wang B 《Molecular biotechnology》2007,36(2):102-112
N-methylation of phosphoethanolamine, the committing step in choline (Cho) biosynthesis in plants, is catalyzed by S-adenosyl-l-methionine: phosphoethanolamine N-methyltransferase (PEAMT, EC 2.1.1.103). Herein we report the cloning and characterization of the novel maize phosphoethanolamine
N-methyltransferase gene (ZmPEAMT1) using a combination of bioinformatics and a PCR-based allele mining strategy. The cDNA sequence of ZmPEAMT1 gene is 1,806 bp in length and translates a 495 amino acids peptide. The upstream promoter sequence of ZmPEAMT1 were obtained by TAIL-PCR, and contained four kinds of putative cis-acting regulatory elements, including stress-responsive elements, phytohormone-responsive elements, pollen developmental
special activation elements, and light-induced signal transduction elements, as well as several other structural features
in common with the promoter of rice and Arabidopsis homologies. RT-PCR analysis showed that expression of ZmPEAMT1 was induced by salt stress and suppressed by high temperature. Over-expression of ZmPEAMT1 enhanced the salt tolerance, root length, and silique number in transgenic Arabidopsis. These data indicated that ZmPEAMT1 maybe involved in maize root development and stress resistance, and maybe having a potential application in maize genetic
engineering.
Note: Nucleotide sequence data are available in GenBank under the following accession numbers: maize (Zea mays, ZmPEAMT1, AY626156; ZmPEAMT2, AY103779); rice (Oryza sativa, OsPEAMT1/Os01g50030, NM_192178; OsPEAMT2/Os05g47540, XM_475841); wheat (Triticum aestivum, TaPEAMT, AY065971); Arabidopsis (Arabidopsis thaliana, AtNMT1/At3g18000, AY091683; AtNMT2/At1g48600, NM_202264; AtNMT3/At1g73600, NM_106018); oilseed rape (Brassica napus, BnPEAMT, AY319479), tomato (Lycopersicon esculentum, AF328858), spinach (Spinacia oleracea, AF237633). 相似文献
16.
17.
K. Kapsopoulou A. Mourtzini M. Anthoulas E. Nerantzis 《World journal of microbiology & biotechnology》2007,23(5):735-739
Four mixed culture fermentations of grape must were carried out with Kluyveromyces thermotolerans strain TH941 and Saccharomyces cerevisiae strain SCM952. In the first culture, both yeasts were added together, whereas in the remaining three cultures S. cerevisiae was added 1, 2, and 3 days after the inoculation of K. thermotolerans. The growth and survival of the K. thermotolerans strain and the amount of the produced l-lactic acid depend on the time of inoculation of the S. cerevisiae strain and provided an effective acidification during alcoholic fermentation. The four cultures contained, respectively,
at the end of fermentation 0.18, 1.80, 4.28, and 5.13 g l-lactic acid l−1. The grape must with an initial pH of 3.50 was effectively acidified (70% increase in titratable acidity, 0.30 pH unit decrease)
by the production of 5.13 g l-lactic acid l−1. 相似文献
18.
Ma C Gao C Qiu J Hao J Liu W Wang A Zhang Y Wang M Xu P 《Applied microbiology and biotechnology》2007,77(1):91-98
Pseudomonas stutzeri SDM was newly isolated from soil, and two stereospecific NAD-independent lactate dehydrogenase (iLDH) activities were detected
in membrane of the cells cultured in a medium containing dl-lactate as the sole carbon source. Neither enzyme activities was constitutive, but both of them might be induced by either
enantiomer of lactate. P. stutzeri SDM preferred to utilize lactate to growth, when both l-lactate and glucose were available, and the consumption of glucose was observed only after lactate had been exhausted. The
Michaelis–Menten constant for l-lactate was higher than that for d-lactate. The l-iLDH activity was more stable at 55°C, while the d-iLDH activity was lost. Both enzymes exhibited different solubilization with different detergents and different oxidation
rates with different electron acceptors. Combining activity staining and previous proteomic analysis, the results suggest
that there are two separate enzymes in P. stutzeri SDM, which play an important role in converting lactate to pyruvate.
Ma and Gao contributed equally to this work. 相似文献
19.
M. Helanto K. Kiviharju T. Granström M. Leisola A. Nyyssölä 《Applied microbiology and biotechnology》2009,83(1):77-83
l-Ribose is a rare and expensive sugar that can be used as a precursor for the production of l-nucleoside analogues, which are used as antiviral drugs. In this work, we describe a novel way of producing l-ribose from the readily available raw material l-arabinose. This was achieved by introducing l-ribose isomerase activity into l-ribulokinase-deficient Escherichia coli UP1110 and Lactobacillus plantarum BPT197 strains. The process for l-ribose production by resting cells was investigated. The initial l-ribose production rates at 39°C and pH 8 were 0.46 ± 0.01 g g−1 h−1 (1.84 ± 0.03 g l−1 h−1) and 0.27 ± 0.01 g g−1 h−1 (1.91 ± 0.1 g l−1 h−1) for E. coli and for L. plantarum, respectively. Conversions were around 20% at their highest in the experiments. Also partially purified protein precipitates
having both l-arabinose isomerase and l-ribose isomerase activity were successfully used for converting l-arabinose to l-ribose. 相似文献
20.
Sanjay Kumar K. Pakshirajan V. Venkata Dasu 《Applied microbiology and biotechnology》2009,84(3):477-486
Glutaminase-free l-asparaginase is known to be an excellent anticancer agent. In the present study, statistically based experimental designs
were applied to maximize the production of glutaminase-free l-asparaginase from Pectobacterium carotovorum MTCC 1428. Nine components of the medium were examined for their significance on the production of l-asparaginase using the Plackett–Burman experimental design. The medium components, viz., glucose, l-asparagine, KH2PO4, and MgSO4·7H2O, were screened based on their high confidence levels (P < 0.04). The optimum levels of glucose, l-asparagine, KH2PO4, and MgSO4·7H2O were found to be 2.076, 5.202, 1.773, and 0.373 g L−1, respectively, using the central composite experimental design. The maximum specific activity of l-asparaginase in the optimized medium was 27.88 U mg−1 of protein, resulting in an overall 8.3-fold increase in the production compared to the unoptimized medium. 相似文献