共查询到20条相似文献,搜索用时 15 毫秒
1.
Emi Miyamoto Yuri Tanioka Ayako Nishizawa-Yokoi Yukinori Yabuta Kouhei Ohnishi Haruo Misono Shigeru Shigeoka Yoshihisa Nakano Fumio Watanabe 《Archives of microbiology》2010,192(6):437-446
Significant accumulation of the methylmalonyl-CoA mutase apoenzyme was observed in the photosynthetic flagellate Euglena gracilis Z at the end of the logarithmic growth phase. The apoenzyme was converted to a holoenzyme by incubation for 4 h at 4°C with
10 μM 5′-deoxyadenosylcobalamin, and then, the holoenzyme was purified to homogeneity and characterized. The apparent molecular
mass of the enzyme was calculated to be 149.0 kDa ± 5.0 kDa using Superdex 200 gel filtration. SDS–polyacrylamide gel electrophoresis
of the purified enzyme yielded a single protein band with an apparent molecular mass of 75.0 kDa ± 3.0 kDa, indicating that
the Euglena enzyme is composed of two identical subunits. The purified enzyme contained one mole of prosthetic 5′-deoxyadenosylcobalamin
per mole of the enzyme subunit. Moreover, we cloned the full-length cDNA of the Euglena enzyme. The cDNA clone contained an open reading frame encoding a protein of 717 amino acids with a calculated molecular
mass of 78.3 kDa, preceded by a putative mitochondrial targeting signal consisting of nine amino acid residues. Furthermore,
we studied some properties and physiological function of the Euglena enzyme. 相似文献
2.
Sumra Afzal Mahjabeen Saleem Riffat Yasmin Mamoona Naz Muhammad Imran 《Molecular biology reports》2010,37(4):1717-1723
Consistent with its precloning characterization from the cellulolytic Bacillus sp., β-1,4-endoglucanase purified from the recombinant E. coli exhibited maximum activity at 60°C and pH 7.0. It was highly specific for CMC hydrolysis, with stability up to 70°C and over
a pH range of 6.0–8.0. The K
m and V
max values for CMCase activity of the enzyme were 4.1 mg/ml and 25 μmole/ml min−1, respectively. The purified enzyme was a monomer of 65 kDa, as determined by SDS-PAGE. The presence of sucrose and IPTG in
fermentation media increased the endoglucanase activity of the recombinant enzyme to 5.2-folds as compared with that of the
actual one. 相似文献
3.
Jeyaraman Vikramathithan Gali Nirmal kumar Pandurangan Muthuraman Kotteazeth Srikumar 《The protein journal》2010,29(7):481-486
A thermo stable xylanase was purified and characterized from the cladodes of Cereus pterogonus plant species. The enzyme was purified to homogeneity by ammonium sulfate (80%) fractionation, ion exchange and size exclusion
chromatography. The enzyme showed a final specific activity of 216.2 U/mg and the molecular mass of the protein was 80 KDa.
The optimum pH and temperature for xylanase activity were 5.0 and 80 °C, respectively,. With oat spelt xylan as a substrate
the enzyme yielded a Km value of 2.24 mg/mL and a Vmax of 5.8 μmol min−1 mg−1. In the presence of metal ions (1 mM) such as Co2+,Mn2+, Ni2+, Ca2+ and Fe3+ the activity of the enzyme increased, where as strong inhibition of the enzyme activity was observed with the use of Hg2+, Cd2+, Cu2+, while partial inhibition was noted with Zn2+ and Mg2+. The substrate specificity of the xylanase yielded maximum activity with oat spelt xylan. 相似文献
4.
5.
Purification of extracellular α-amylase from Bacillus subtilis KIBGE HAS was carried out by ultrafiltration, ammonium sulfate precipitation and gel filtration chromatography. The enzyme
was purified to homogeneity with 96.3-fold purification with specific activity of 13011 U/mg. The molecular weight of purified
α-amylase was found to be 56,000 Da by SDS-PAGE. Characteristics of extracellular α-amylase showed that the enzyme had a Km
and V
max value of 2.68 mg/ml and 1773 U/ml, respectively. The optimum activity was observed at pH 7.5 in 0.1 M phosphate buffer at
50°C. The amino acid composition of the enzyme showed that the enzyme is rich in neutral/non polar amino acids and less in
acidic/polar and basic amino acids. The N-terminal protein sequence of 10 residues was found to be as Ser-Ser-Asn-Lys-Leu-Thr-Thr-Ser-Trp-Gly
(S-S-N-K-L-T-T-S-W-G). Furthermore, the protein was not N-terminally blocked. The sequence of α-amylase from B. subtilis KIBGE HAS was a novel sequence and showed no homology to other reported α-amylases from Bacillus strain. 相似文献
6.
Thioredoxin reductase (TrxR, EC 1.6.4.5) of Deinococcus radiophilus was purified by steps of sonication, ammonium sulfate fractionation, 2′5′ ADP Sepharose 4B affinity chromatography, and Sephadex
G-100 gel filtration. The purified TrxR, which was active with both NADPH and NADH, gave a 368 U/mg protein of specific activity
with 478-fold purification and 18% recovery from the cell-free extract. An isoelectric point of the purified enzymes was ca.
4.5. The molecular weights of the purified TrxR estimated by PAGE and gel filtration were about 63.1 and 72.2 kDa, respectively.
The molecular mass of a TrxR subunit is 37 kDa. This suggests that TrxR definitely belongs to low molecular weight TrxR (L-TrxR).
The Km and Vmax of TrxR for NADPH are 12.5 μM and 25 μM/min, whereas those for NADH are 30.2 μM and 192 μM/min. The Km and
Vmax for 5, 5′-dithio-bis-2-nitrobenzoic acid (DTNB, a substituted substrate for thioredoxin) are 463 μM and 756 μM/min, respectively.
The presence of FAD in TrxR was confirmed with the absorbance peaks at 385 and 460 nm. The purified TrxR was quite stable
from pH 3 to 9, and was thermo-stable up to 70°C. TrxR activity was drastically reduced (ca. 70%) by Cu2+, Zn2+, Hg2+, and Cd2+, but moderately reduced (ca. 50%) by Ag+. A significant inhibition of TrxR by N-ethylmaleimide suggests an occurrence of cysteine at its active sites. Amino acid
sequences at the N-terminus of purified TrxR are H2N-Ser-Glu-Gln-Ala-Gln-Met-Tyr-Asp-Val-Ile-Ile-Val-Gly-Gly-Gly-Pro-Ala-Gly-Leu-Thr-Ala-COOH. These sequences show high similarity
with TrxRs reported in Archaea, such as Methanosarcina mazei, Archaeoglobus fulgidus etc. 相似文献
7.
Dai-Eun Sok 《Neurochemical research》1996,21(10):1193-1199
A Zn2+-glycerophosphocholine cholinephosphodiesterase was purified with a specific activity of 4.6 μmole/min·mg protein from bovine
brain membranes by procedures involving PI-PLC solubilization, concanavalin A affinity chromatography, CM-sephadex chromatography
and Sephadex G-150 chromatography. Based on molecular weight determination gel chromatography and SDS polyacrylamide gel electrophoresis,
the phosphodiesterase activity appears to be a dimeric protein (110 kDa) composed of two subunits with a molecular weight
of approximately 54 kDa. The Km value for p-nitrophenylphosphocholine and the optimum pH were found to be 16 μM and pH 10.5,
respectively. The phosphodiesterase was inhibited by Cu2+, but not the other divalent metal ions. The activity of the apoenzyme was remarkably activated by Co2+ or Zn2+, but not Mn2+ or Mg2+. In addition, the inactivation of the enzyme in glycine buffer was prevented by Mn2+ or Zn2+, but not Co2+ or Mg2. In a separate experiment, comparing properties of the purified and membrane-bound phosphodiesterases, the forms of two enzymes
were quite similar except in stability. Both enzymes were more stable at pH 7.4 than pH 5 or 10. However, the membrane-bound
enzyme was more stable than the soluble enzyme at all three pHs. These data suggest that the activity of the phosphodiesterase
may be stabilized in-vivo. 相似文献
8.
Laila Oukhattar Tarik Baibai Adnane Moutaouakkil Omar Assobhei Abdelaziz Soukri 《Reviews in Fish Biology and Fisheries》2008,18(3):263-271
The NAD+ dependent cytosolic Glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) from arms of Octopus vulgaris, Cuvier, 1787, (Octopoda, Cephalopoda) was purified to homogeneity and its kinetic properties investigated. The purification
method consisted of ammonium sulfate fractionation followed by Blue Sepharose CL-6B chromatography resulting in a 26-fold
increase in specific activity and a final yield of approximately 16%. The apparent molecular weight of the purified native
enzyme was 153 kDa. The protein is an homotetramer, composed of identical subunits with an apparent molecular weight of approximately
36 kDa. The Michaelis constants Km for both NAD+ and d-G3P were 66 μM and 320 μM, respectively. The maximal velocity Vmax of the purified enzyme was estimated to be 21.8 U/mg. Only one GAPDH isoform (pI 6.6) was obtained by isoelectrofocusing in polyacrylamide slab gels holding ampholyte generated pH gradients. Under the conditions
of assay, the optimum activity occurs at pH 7.0 and at temperature of 35°C. Polyclonal antibodies raised in rabbits against
the purified GAPDH immunostained a single 36 kDa GAPDH band on crude extract protein preparations blotted onto nitrocellulose. 相似文献
9.
Formaldehyde activating enzyme (Fae) was first discovered in methylotrophic bacteria, where it is involved in the oxidation
of methanol to CO2 and in formaldehyde detoxification. The 18 kDa protein catalyzes the condensation of formaldehyde with tetrahydromethanopterin
(H4MPT) to methylene-H4MPT. We describe here that Fae is also present and functional in the methanogenic archaeon Methanosarcina barkeri. The faeA homologue in the genome of M. barkeri was heterologously expressed in Escherichia coli and the overproduced purified protein shown to actively catalyze the condensation reaction: apparent V
max=13 U/mg protein (1 U=μmol/min); apparent Km for H4MPT=30 μM; apparent Km for formaldehyde=0.1 mM. By Western blot analysis the concentration of Fae in cell extracts of M. barkeri was determined to be in the order of 0.1% of the soluble cell proteins. Besides the faeA gene the genome of M. barkeri harbors a second gene, faeB-hpsB, which is shown to code for a 42 kDa protein with both Fae activity (3.6 U/mg) and hexulose-6-phosphate synthase (Hps) activity
(4.4 U/mg). The results support the recent proposal that in methanogenic archaea Fae and Hps could have a function in ribose
phosphate synthesis. 相似文献
10.
Sugimoto S Sugimoto H Aoyama C Aso C Mori M Izumi T 《Biochimica et biophysica acta》2006,1761(12):1410-1418
A lysophospholipase D (lysoPLD) was purified to apparent homogeneity from rat brain nuclear fractions using 1-[(14)C]palmitoyl-glycerophosphorylcholine as a substrate. The abundance of autotaxin (ATX), a secretory lysoPLD, was also estimated for each fraction. The nuclear fraction had relatively high levels of lysoPLD activity but weak immunoreactivity with an anti-ATX antibody. LysoPLD activity was further purified 5550-fold by sequential chromatography. The final preparation migrated as a single band with a molecular weight of 35,000. Anti-ATX antibodies did not cross-react with the purified enzyme. Moreover, enzyme activity was highest at pH 7.0-7.5 and requires Mg(2+). The Km and Vmax values for 1-palmitoyl-glycerophosphorylcholine were 176 microM and 0.3 micromol/min/mg, respectively. The purified enzyme hydrolyzed saturated forms of LPC more robustly than unsaturated forms. The enzyme could hydrolyze platelet-activating factor (PAF) to the same extent as 16:0-LPC, and showed a higher activity toward lysoPAF (1-O-hexadecyl-2-lyso-glycerophosphorylcholine). These results suggested that the lysoPLD purified from rat brain nuclear fractions in this work is a novel enzyme that hydrolyzes lysoPAF, PAF, and LPC to liberate choline. 相似文献
11.
Hartinger D Schwartz H Hametner C Schatzmayr G Haltrich D Moll WD 《Applied microbiology and biotechnology》2011,91(3):757-768
Fumonisins are carcinogenic mycotoxins that are frequently found as natural contaminants in maize from warm climate regions
around the world. The aminotransferase FumI is encoded as part of a gene cluster of Sphingopyxis sp. MTA144, which enables this bacterial strain to degrade fumonisin B1 and related fumonisins. FumI catalyzes the deamination of the first intermediate of the catabolic pathway, hydrolyzed fumonisin
B1. We used a preparation of purified, His-tagged FumI, produced recombinantly in Escherichia coli in soluble form, for enzyme characterization. The structure of the reaction product was studied by NMR and identified as
2-keto hydrolyzed fumonisin B1. Pyruvate was found to be the preferred co-substrate and amino group receptor (K
M = 490 μM at 10 μM hydrolyzed fumonisin B1) of FumI, but other α-keto acids were also accepted as co-substrates. Addition of the co-enzyme pyridoxal phosphate to the
enzyme preparation enhanced activity, and saturation was already reached at the lowest tested concentration of 10 μM. The
enzyme showed activity in the range of pH 6 to 10 with an optimum at pH 8.5, and in the range of 6°C to 50°C with an optimum
at 35°C. The aminotransferase worked best at low salt concentration. FumI activity could be recovered after preincubation
at pH 4.0 or higher, but not lower. The aminotransferase was denatured after preincubation at 60°C for 1 h, and the residual
activity was also reduced after preincubation at lower temperatures. At optimum conditions, the kinetic parameters K
M = 1.1 μM and k
cat = 104/min were determined with 5 mM pyruvate as co-substrate. Based on the enzyme characteristics, a technological application
of FumI, in combination with the fumonisin carboxylesterase FumD for hydrolysis of fumonisins, for deamination and detoxification
of hydrolyzed fumonisins seems possible, if the enzyme properties are considered. 相似文献
12.
Purification and properties of creatinine iminohydrolase from Flavobacterium filamentosum 总被引:2,自引:0,他引:2
Creatinine iminohydrolase (EC 3.5.4.21), which catalyzes hydrolysis of creatinine to N-methylhydantoin and ammonia, was purified from Flavobacterium filamentosum. The average molecular weight of the purified enzyme was 272,480, and the subunit molecular weight was 44,300. Extensive specificity studies indicated that the enzyme utilized cytosine (Km, 0.62 mM; Vm, 20.1 units/mg) as well as creatinine (Km, 5.00 mM; Vm, 40.4 units/mg) as a substrate. Each was a competitive inhibitor toward hydrolysis of the other compound. Dialysis of creatinine iminohydrolase in the presence of 0.01 M Tris phosphate buffer, pH 7.5, containing 1,10-phenanthroline decreased activity by 98%. Reactivation was accomplished by incubating the apoenzyme in the presence of certain divalent metal chlorides, listed in decreasing order of effectiveness: iron(II), zinc, cobalt(II), cadmium, and nickel. The extent of reactivation depended on the substrate and on which metal ion was added to the apoenzyme. Creatinine to cytosine activity ratios varied from 1:3.75 (iron(II) chloride), to 1:0.9 (zinc chloride), to 1:0.06 (nickel chloride). For different preparations of the holoenzyme that ratio ranged from 1:0.45 to 1:1.10. Variable but significant quantities of zinc and iron were present in all preparations of the purified enzyme. 相似文献
13.
Mohammad Shafiei Abed-Ali Ziaee Mohammad Ali Amoozegar 《Journal of industrial microbiology & biotechnology》2011,38(2):275-281
A halophilic α-amylase produced by Nesterenkonia sp. strain F was purified to homogeneity by 80% ethanol precipitation, Q-Sepharose anion exchange, and Sephacryl S-200 gel
filtration chromatography. The purified amylase exhibited specific activity of 357 unit/mg protein that corresponds to twofold
purification. The molecular mass of the amylase was determined to be 57 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis
(SDS-PAGE) and gel filtration chromatography. The optimal pH and temperature for enzyme activity were 6.5 and 45°C, respectively.
The amylase was active over a wide range of salt concentrations (0–4 M) with maximum activity at 0.75–1 M NaCl. The α-amylase
activity was stimulated by Ca2+ and inhibited by ethylenediamine tetraacetic acid (EDTA), suggesting that this enzyme is a metalloenzyme. The purified enzyme
showed remarkable stability towards surfactants (Tween 20, Tween 80, and Triton X-100), and its activity was increased by
β-mercaptoethanol. The halophilic α-amylase was stable in the presence of various organic solvents such as benzene, chloroform,
toluene, and cyclohexane. These properties indicate wide potential applications of this α-amylase in starch-processing industries. 相似文献
14.
The chemolithoautotroph, Arthrobacter sp.15b oxidizes arsenite to arsenate using a membrane bound arsenite oxidase. The enzyme arsenite oxidase is purified to
its homogeneity and identified using MALDI-TOF MS analysis. Upon further characterization, it was observed that the enzyme
is a heterodimer showing native molecular mass as ~100 kDa and appeared as two subunits of ~85 kDa LSU and 14 kDa SSU on SDS–PAGE.
The V
max and K
m values of the enzyme was found to be 2.45 μM (AsIII)/min/mg) and 26 μM, respectively. The purified enzyme could withstand
wide range of pH and temperature changes. The enzyme, however, gets deactivated in the presence of 1 mM of DEPC suggesting
the involvement of histidine at the binding site of the enzyme. The peptide analysis of large sub unit of the enzyme showed
close match with the arsenite oxidases of Burkholderia sp. YI019A and arsenite oxidase, Mo-pterin containing subunit of Alcaligenes
faecalis. The small subunit, however, differed from other arsenite oxidases and matched only with 2Fe–2S binding protein of Anaplasma
phagocytophilum. This indicates that Rieske subunits containing the iron–sulfur clusters present in the large as well as small subunits of
the enzyme are integral part of the protein. 相似文献
15.
Glucose-6-phosphate dehydrogenase (G6PD) was purified from rat small intestine with 19.2% yield and had a specific activity of 53.8 units per miligram protein. The pH optimum was determined to be 8.1. The purified rat small intestinal G6PD gave one activity, one protein band on native PAGE. The observation of one band on SDS/PAGE with an Mr of 48 kDa and a specific activity lower than expected may suggest the proteolytically affected enzyme or different form of G6PD in the rat small intestine. The activation energy, activation enthalpy, Q10, and optimum temperature from Arrhenius plot for the rat small intestinal G6PD were found to be 8.52 kcal/mol, 7.90 kcal/mol, 1.59, and 38 degrees C, respectively. The Km values for G6P and NADP+ were 70.1 +/- 20.8 and 23.2 +/- 7.6 microM, respectively. Double-reciprocal plots of 1/Vm versus 1/G6P (at constant [NADP+]) and of 1/Vm versus 1/NADP+ at constant [G6P]) intersected at the same point on the 1/Vm axis to give Vm = 53.8 U/mg protein. 相似文献
16.
J. E. Gomes Júnior D. S. L. Souza R. M. Nascimento A. L. M. Lima J. A. T. Melo T. L. Rocha R. N. G. Miller O. L. Franco M. F. Grossi-de-Sa L. R. D. Abreu 《The protein journal》2010,29(3):188-194
A β-N-Acetylhexosaminidase (EC 3.2.1.52) was purified from hepatic extracts of Sotalia fluviatilis, order Cetacea. The protein was purified by using ammonium sulfate fractionation and four subsequent chromatographies (Biogel
A 1.5 m, Chitin, Deae-Biogel and hydroxyapatite resins). After these purification steps, the enzyme was purified 380.5-fold
with an 8.4% yield. The molecular mass (10 kDa) was estimated by SDS–PAGE and MALDI-TOF analysis. A Km of 2.72 mM and Vmax
9.5 × 10−6 μmol/(min.mg) were found for this enzyme, determined by p-nitrophenyl-β-d-hexosaminide substrate digestion. Optimal pH and temperature for β-N-Acetylhexosaminidase activity were 5.0 and 60 °C, respectively.
Enzyme activity was inhibited by sodium selenate (Na2SeO4), mercuric chloride (HgCl2) and sodium dodecyl sulfate (C12H25SO4Na), and activated by zinc, calcium, barium and lithium ions. Characterization of the β-N-Acetylhexosaminidase in Sotalia fluviatilis can be a basis for physiological studies in this species. 相似文献
17.
Ma YB Zhang ZF Shao MY Kang KH Shi XL Dong YP Li JL 《Marine biotechnology (New York, N.Y.)》2012,14(2):245-251
Sulfide is a natural, widely distributed, poisonous substance, and sulfide:quinone oxidoreductase (SQR) is responsible for
the initial oxidation of sulfide in mitochondria. In this study, we examined the response of SQR to sulfide exposure (25,
50, and 150 μM) at mRNA, protein, and enzyme activity levels in the body wall and hindgut of the echiuran worm Urechis unicinctus, a benthic organism living in marine sediments. The results revealed SQR mRNA expression during sulfide exposure in the body
wall and hindgut increased in a time- and concentration-dependent manner that increased significantly at 12 h and continuously
increased with time. At the protein level, SQR expression in the two tissues showed a time-dependent relationship that increased
significantly at 12 h in 50 μM sulfide and 6 h in 150 μM, and then continued to increase with time while no significant increase
appeared after 25 μM sulfide exposure. SQR enzyme activity in both tissues increased significantly in a time-dependent manner
after 50 μM sulfide exposure. We concluded that SQR expression could be induced by sulfide exposure and that the two tissues
studied have dissimilar sulfide metabolic patterns. A U. unicinctus sulfide-induced detoxification mechanism was also discussed. 相似文献
18.
Characterization of a thermostable lipase showing loss of secondary structure at ambient temperature
Sharma PK Singh K Singh R Capalash N Ali A Mohammad O Kaur J 《Molecular biology reports》2012,39(3):2795-2804
A gene encoding extracellular lipase was cloned and characterized from metagenomic DNA extracted from hot spring soil. The
recombinant gene was expressed in E. coli and expressed protein was purified to homogeneity using hydrophobic interactions chromatography. The mature polypeptide consists
of 388 amino acids with apparent molecular weight of 43 kDa. The enzyme displayed maximum activity at 50°C and pH 9.0. It
showed thermal stability up to 40°C without any loss of enzyme activity. Nearly 80% enzyme activity was retained at 50°C even
after incubation for 75 min. However above 50°C the enzyme displayed thermal instability. The half life of the enzyme was
determined to be 5 min at 60°C. Interestingly the CD spectroscopic study carried out in the temperature range of 25–95°C revealed
distortion in solution structure above 35°C. However the intrinsic tryptophan fluorescence spectroscopic study revealed that
even with the loss of secondary structure at 35°C and above the tertiary structure was retained. With p-nitrophenyl laurate as a substrate, the enzyme exhibited a K
m
, V
max
and K
cat
of 0.73 ± 0.18 μM, 239 ± 16 μmol/ml/min and 569 s−1 respectively. Enzyme activity was strongly inhibited by CuCl2, HgCl2 and DEPC but not by PMSF, eserine and SDS. The protein retained significant activity (~70%) with Triton X-100. The enzyme
displayed 100% activity in presence of 30% n-Hexane and acetone. 相似文献
19.
巨大芽孢杆菌产胞外青霉素酰化酶发酵液经硫酸铵分级抽提及SephadexG-100、羟基磷灰石、DEAE纤维素DE52等层析步骤,提纯了青霉素酰化酶,得到电泳均一的酶制剂。纯酶比活力约为25U/mg蛋白,纯化49倍,活力回收58%,经PAGE及SDS-PAGE测知该酶不含亚基,其分子量约为140kD。该酶最适pH为9.0,最适温度47℃,用底物NIPAB测活,其Km值为6.2×10~(-4)mol/L,Vm值为1.24×104mol/L。此外还探讨了部分金属离子对该酶的影响。 相似文献
20.
Chengtao Wang Yanping Cao Baoguo Sun Baoping Ji M. J. Robert Nout Ji Wang Yonghuan Zhao 《World journal of microbiology & biotechnology》2008,24(10):2149-2157
Rhodococcus sp. R14-2, isolated from Chinese Jin-hua ham, produces a novel extracellular cholesterol oxidase (COX). The enzyme was extracted from
fermentation broth and purified 53.1-fold based on specific activity. The purified enzyme shows a single polypeptide band
on SDS-PAGE with an estimated molecular weight of about 60 kDa, and has a pI of 8.5. The first 10 amino acid residues of the NH2-terminal sequence of the enzyme are A-P-P-V-A-S-C-R-Y-C, which differs from other known COXs. The enzyme is stable over a
rather wide pH range of 4.0–10.0. The optimum pH and temperature of the COX are pH 7.0 and 50°C, respectively. The COX rapidly
oxidizes 3β-hydroxysteroids such as cholesterol and phytosterols, but is inert toward 3α-hydroxysteroids. Thus, the presence
of a 3β-hydroxyl group appears to be essential for substrate activity. The Michaelis constant (Km) for cholesterol is estimated
at 55 μM; the COX activity was markedly inhibited by metal ions such as Hg2+ and Fe3+ and inhibitors such as p-chloromercuric benzoate, mercaptoethanol and fenpropimorph. Inhibition caused by p-chloromercuric benzoate, mercuric chloride, or silver nitrate was almost completely prevented by the addition of glutathione.
These suggests that -SH groups may be involved in the catalytic activity of the present COX. 相似文献