共查询到20条相似文献,搜索用时 15 毫秒
1.
Durmaz-Sam S Sayar NA Topal-Sarikaya A Sayar AA 《Bioprocess and biosystems engineering》2011,34(8):997-1005
The potential of the dried yeast, wild-type Schizosaccharomyces pombe, to remove Ni(II) ion was investigated in batch mode under varying experimental conditions including pH, temperature, initial
metal ion concentration and biosorbent dose. Optimum pH for biosorption was determined as 5.0. The highest equilibrium uptake
of Ni(II) on S. pombe, q
e, was obtained at 25 °C as 33.8 mg g−1. It decreased with increasing temperature within a range of 25–50 °C denoting an exothermic behaviour. Increasing initial
Ni(II) concentration up to 400 mg L−1 also elevated equilibrium uptake. No more adsorption took place beyond 400 mg L−1. Equilibrium data fitted better to Langmuir model rather than Freundlich model. Sips, Redlich–Peterson, and Kahn isotherm
equations modelled the investigated system with a performance not better than Langmuir. Kinetic model evaluations showed that
Ni(II) biosorption process followed the pseudo-second order rate model while rate constants decreased with increasing temperature.
Gibbs free energy changes (ΔG°) of the system at 25, 30, 35 and 50 °C were found as −1.47E + 4, −1.49E + 4, −1.51E + 4, and −1.58E + 4 J mol−1, respectively. Enthalpy change (ΔH°) was determined as −2.57E + 3 J mol−1 which also supports the observed exothermic behaviour of the biosorption process. Entropy change (ΔS°) had a positive value (40.75 J mol−1 K−1) indicating an increase in randomness during biosorption process. Consequently, S. pombe was found to be a potential low-cost agent for Ni(II) in slightly acidic aqueous medium. In parallel, it has been assumed
to act as a separating agent for Ni(II) recovery from its aqueous solution. 相似文献
2.
Recent work on the bacterial iron–sulfur cluster (isc) family of gene products, and eukaryotic homologs, has advanced the molecular understanding of cellular mechanisms of iron–sulfur
cluster biosynthesis. Members of the IscS family are pyridoxyl-5′-phosophate dependent proteins that deliver inorganic sulfide
during assembly of the [2Fe–2S] cluster on the IscU scaffold protein. Herein it is demonstrated through calorimetry, fluorescence,
and protein stability measurements that Thermotoga maritima IscS forms a 1:1 complex with IscU in a concentration-dependent manner (K
D varying from 6 to 34 μM, over an IscS concentration range of approximately 2–50 μM). Docking simulations of representative
IscU and IscS proteins reveal critical contact surfaces at the N-terminal helix of IscU and a C-terminal loop comprising a
chaperone binding domain. Consistent with the isothermal titration calorimetry results described here, an overall dominant
contribution of charged surfaces with a change in the molar heat capacity of binding, ΔC
p ~ 199.8 kcal K−1 mol−1, is observed that accounts for approximately 10% of the total accessible surface area at the binding interface. Both apo
and holo IscUs and homologs were found to bind to IscS in an enthalpically driven reaction with comparable K
D values. Both helix and loop regions are highly conserved among phylogenetically diverse organisms from a pool of archael,
bacterial, fungal, and mammalian representatives. 相似文献
3.
Syed Ali Imran Bokhari Farooq Latif Muhammad Ibrahim Rajoka 《World journal of microbiology & biotechnology》2009,25(3):493-502
Xylanases produced from a locally isolated strain of Thermomyces lanuginosus and its mutant derivative were purified to a yield of 39.1 and 42.83% with specific activities of 15,501 and 17,778 IU mg−1 protein, respectively. The purification consisted of two steps i.e., ammonium sulphate precipitation, and gel filtration
chromatography. The mutant enzyme showed high affinity for substrate, with a K
m of 0.098 mg ml−1 as compared to wild type enzyme showing K
m of not less than 0.112 mg ml−1. It was found that pH values of 8.1 and 7.3 were best for activity of the mutant and wild-type-derived enzymes, respectively.
The values of pK
a of the acidic limbs of both enzymes were the same (5.0 and 4.9, respectively) but the pK
a value of the basic limb was slightly increased, indicating the participation of a carboxyl group present in a non-polar environment.
Temperatures of 70 and 65°C were found optimal for mutant and wild-derived xylanase, respectively. Enzymes displayed a high
thermostability showing a half life of 31.79 and 6.0 min (5.3-fold improvement), enthalpy of denaturation (ΔH*) of 146.06 and 166.95 kJ mol−1, entropy of denaturation (ΔS*) of 101.44 and 174.67, and free energy of denaturation (ΔG*) of 110.25 and 105.29 kJ mol−1 for mutant- and wild-organism derived enzyme, respectively at 80°C. Studies on the folding and stability of cellulase-less
xylanases are important, since their biotechnological employments require them to function under extreme conditions of pH
and temperature. The kinetic and thermodynamic properties suggested that the xylanase from the mutant organism is better as
compared to xylanase produced from the wild type and previously reported strains of same species, and may have a potential
usage in various industrial fields. 相似文献
4.
M.I. Rajoka Khalil-ur- Rehman Tehmina Tabish M.A. Zia 《World journal of microbiology & biotechnology》2006,22(3):289-291
Purified uricase from a caprine kidney, possessed K
m
and V
max values of 1.1 mg ml−1 and 3512 IU (mg protein)−1 for uric acid hydrolysis, respectively. The optimum temperature and pH for catalytic activity were 40 °C and 8.5, respectively.
The activation energy for formation of ES complex was 13.6 kJ mol−1. Enthalpy (ΔH*), entropy of activation (ΔS*) and Gibbs free energy demand of uricase inactivation were 62.8 kJ mol−1, −102 J mol−1 K−1 and 104.3 kJ mol−1, respectively. Gibbs free enrgy demand for substrate binding and transition state stabilization were also determined which
were comparable with those for themostable enzymes. 相似文献
5.
Agu Laisk Eero Talts Vello Oja Hillar Eichelmann Richard B. Peterson 《Photosynthesis research》2010,103(2):79-95
Fast cyclic electron transport (CET) around photosystem I (PS I) was observed in sunflower (Helianthus annuus L.) leaves under intense far-red light (FRL) of up to 200 μmol quanta m−2 s−1. The electron transport rate (ETR) through PS I was found from the FRL-dark transmittance change at 810 and 950 nm, which
was deconvoluted into redox states and pool sizes of P700, plastocyanin (PC) and cytochrome f (Cyt f). PC and P700 were in
redox equilibrium with K
e = 35 (ΔE
m = 90 mV). PS II ETR was based on O2 evolution. CET [(PS I ETR) − (PS II ETR)] increased to 50–70 μmol e− m−2 s−1 when linear electron transport (LET) under FRL was limited to 5 μmol e− m−2 s−1 in a gas phase containing 20–40 μmol CO2 mol−1 and 20 μmol O2 mol−1. Under these conditions, pulse-saturated fluorescence yield F
m was non-photochemically quenched; however, F
m was similarly quenched when LET was driven by low green or white light, which energetically precluded the possibility for
active CET. We suggest that under FRL, CET is rather not coupled to transmembrane proton translocation than the CET-coupled
protons are short-circuited via proton channels regulated to open at high ΔpH. A kinetic analysis of CET electron donors and
acceptors suggests the CET pathway is that of the reversed Q-cycle: Fd → (FNR) → Cyt cn → Cyt bh → Cyt bl → Rieske FeS → Cyt f → PC → P700 →→ Fd. CET is activated when PQH2 oxidation is opposed by high ΔpH, and ferredoxin (Fd) is reduced due to low availability of e− acceptors. The physiological significance of CET may be photoprotective, as CET may be regarded as a mechanism of energy
dissipation under stress conditions. 相似文献
6.
An efficient succinic acid production process in a metabolically engineered <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis> strain 总被引:1,自引:0,他引:1
Okino S Noburyu R Suda M Jojima T Inui M Yukawa H 《Applied microbiology and biotechnology》2008,81(3):459-464
A Corynebacterium glutamicum strain (ΔldhA-pCRA717) that overexpresses the pyc gene encoding pyruvate carboxylase while simultaneously exhibiting a disrupted ldhA gene encoding l-lactate dehydrogenase was investigated in detail for succinic acid production. Succinic acid was shown to be efficiently
produced at high-cell density under oxygen deprivation with intermittent addition of sodium bicarbonate and glucose. Succinic
acid concentration reached 1.24 M (146 g l−1) within 46 h. The yields of succinic acid and acetic acid from glucose were 1.40 mol mol−1 (0.92 g g−1) and 0.29 mol mol−1 (0.10 g g−1), respectively. The succinic acid production rate and yield depended on medium bicarbonate concentration rather than glucose
concentration. Consumption of bicarbonate accompanied with succinic acid production implied that added bicarbonate was used
for succinic acid synthesis. 相似文献
7.
The gelation process of mixtures of γ-oryzanol and sitosterol structurants in sunflower oil was studied using light scattering,
rheology, and micro-scanning calorimetry (Micro-DSC). The relation between temperature and the critical aggregation concentration
(CAC) of tubule formation of γ-oryzanol and sitosterol was determined using these techniques. The temperature dependence of
the CAC was used to estimate the binding energy and enthalpic and entropic contribution to the tubular formation process.
The binding energy calculated at the corresponding temperatures and CACs were relatively low, in order of 2 RT (4.5 kJ mol−1), which is in accord with the reversibility of the tubular formation process. The formation of the tubules was associated
with negative (exothermic) enthalpy change (ΔH
0
) compared with positive entropy term (−T ΔS
0 >0), indicating that the aggregation into tubules is an enthalpy-driven process. The oryzanol–sitosterol ratio affected the
aggregation process; solutions with ratio of (60 oryzanol–40 sitosterol) started aggregation at higher temperature compared
with other ratios. 相似文献
8.
Proper determination of the temperature dependence of intrinsic tryptophan fluorescence intensity in native and denatured
states is an essential prerequisite for extracting the free energy of protein unfolding from the thermal denaturation profile.
The most common method employed in determining the temperature dependence of these conformations is through the determination
of slopes of pre- and post-transition baselines. However, simulations of protein unfolding profiles suggest that this method
does not work for marginally stable proteins. We show herein that the temperature dependence of the fluorescence intensity
of N-acetyl tryptophanamide (NATA) in organic solvents and water may be used to represent the temperature dependence of the fluorescence
intensity of tryptophan in native and denatured conformations of a protein, respectively. The wavelength of the emission maximum,
λ
max, of N-acetyl tryptophanamide (NATA) in a particular solvent or tryptophan in proteins is related to the temperature dependence
(m) of its fluorescence intensity by the equation: m (K−1) = (−0.000299 ± 2.2 × 10−5 K−1 nm−1) × λ
max (nm) + (0.0919 ± 0.0025 K−1). 相似文献
9.
P. O. Vardevanyan A. P. Antonyan G. A. Manukyan A. T. Karapetyan A. K. Shchyolkina O. F. Borisova 《Molecular Biology》2000,34(2):272-276
Isotherms of the EtBr adsorption on native and denatured poly(dA)poly(dT) in the temperature interval 20–70°C were obtained.
The EtBr binding constants and the number of binding sites were determined. The thermodynamic parameters of the EtBr intercalation
complex upon changes of solution temperature 20–48°C were calculated: 1.0·106 M−1≤K≤1.4·106 M−1, free energy ΔG
o=−8.7±0.3 kcal/mol, enthalpy ΔH
o≅0, and entropy ΔS
o=28±0.5 cal/(mol deg). UV melting has shown that the melting temperature (T
m) of EtBr-poly(dA)poly(dT) complexes (μ=0.022,4.16·10−5 M EtBr) increased by 17°C as compared with the ΔT
m of free homopolymer, whereas the half-width of the transition (T
m) is not changed. It was shown for the first time that EtBr forms complexes of two types on single-stranded regions of poly(dA)poly(dT)
denatured at 70°C: strong (K
1=1.7·105 M−1; ΔG
o=−8.10±0.03 kcal/mol) and weak (K
2=2.9·103 M−1; ΔG
o=−6.0±0.3 kcal/mol).The ΔG
o of the strong and weak complexes was independent of the solution ionic strength, 0.0022≤μ≤0.022. A model of EtBr binding
with single-stranded regions of poly(dA)poly(dT) is discussed. 相似文献
10.
Claudia Hoffmann Alfred Blume Inge Miller Patrick Garidel 《European biophysics journal : EBJ》2009,38(5):557-568
Therapeutic proteins formulated as liquid solutions at high protein concentration are very sensitive to chemical and physical
degradation. Especially avoiding the formation of protein aggregates is very crucial for product quality. In order to stabilize
the colloidal properties of protein therapeutics various excipient are used. Especially the detergents polysorbate 20 and
80 are common. However, the mechanism upon which the detergents protect the protein from aggregation is not really known.
The present study investigates the interaction of polysorbate 20 and 80 with different proteins: lysozyme, bovine serum albumin
(BSA) and an immunoglobulin. The interaction and binding of the detergents to the proteins is investigated by isothermal titration
calorimetry (ITC). From ITC the thermodynamic parameters (ΔH: change in enthalpy, ΔS: entropy and ΔG: free energy) upon binding are derived as well as the binding constant K
a. The thermal stability of the proteins in the presence of the detergent is assessed by differential scanning calorimetry
(DSC). The results show that both detergents bind to BSA with K
a between 8 and 12 × 103 M−1 with ΔH −50 to −60 kJ/mol (25°C). One to two detergent molecules bind to BSA. The presence of both detergents induces a weak stabilisation
of the thermal denaturation properties of BSA. However, the interaction of polysorbate 20 and 80 with lysozyme and the immunoglobulin
is quite negligible. The presence of the detergents up to a concentration of 2 mM has no impact on the heat capacity curve
neither a destabilisation nor a stabilisation of the native conformation is observed. 相似文献
11.
Isatin-3-isonicotinylhydrazone was synthesized and characterized. The interaction of native calf thymus DNA with isatin-3-isonicotinylhydrazone
(IINH) in 10 mM Tris–HCl aqueous solutions at neutral pH 7.4 has been investigated by spectrophotometric, circular dichroism
(CD), melting temperature (T
m
), spectrofluorimetric, and viscometric techniques. It is found that IINH molecules could intercalate between base pairs of
DNA as are evidenced by: hypochromism in UV absorption band of IINH, induced CD spectral changes, sharp increase in specific
viscosity of DNA, and increase in the fluorescence of methylene blue (MB)-DNA solutions in the presence of increasing amounts
of IINH, which indicates that it is able to release the intercalated MB completely. The binding constants of IINH–DNA complex
at four different temperatures (277, 288, 298, and 310 K) were calculated to be 4.7 × 104, 2.2 × 104, 1.75 × 104 and 1.1 × 104 M−1, respectively. Furthermore, the enthalpy and entropy of the reaction between IINH and CT-DNA showed that the reaction is
enthalpy-favored and entropy- disfavored (∆H = −30.187 kJ mol−1; ∆S = −20.46 J mol−1K−1) which are other evidences to indicate the IINH is able to be intercalated in the DNA base pairs. 相似文献
12.
By simultaneously analyzing the chlorophyll a fluorescence transient and light absorbance at 820 nm as well as chlorophyll fluorescence quenching, we investigated the
effects of different photon flux densities (0, 15, 200 μmol m−2 s−1) with or without 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on the repair process of cucumber (Cucumis sativus L.) leaves after treatment with low temperature (6°C) combined with moderate photon flux density (200 μmol m−2 s−1) for 6 h. Both the maximal photochemical efficiency of Photosystem II (PSII) (F
v/F
m) and the content of active P700 (ΔI/I
o) significantly decreased after chilling treatment under 200 μmol m−2 s−1 light. After the leaves were transferred to 25°C, F
v/F
m recovered quickly under both 200 and 15 μmol m−2 s−1 light. ΔI/I
o recovered quickly under 15 μmol m−2 s−1 light, but the recovery rate of ΔI/I
o was slower than that of F
v/F
m. The cyclic electron transport was inhibited by chilling-light treatment obviously. The recovery of ΔI/I
o was severely suppressed by 200 μmol m−2 s−1 light, whereas a pretreatment with DCMU effectively relieved this suppression. The cyclic electron transport around PSI recovered
in a similar way as the active P700 content did, and the recovery of them was both accelerated by pretreatment with DCMU.
The results indicate that limiting electron transport from PSII to PSI protected PSI from further photoinhibition, accelerating
the recovery of PSI. Under a given photon flux density, faster recovery of PSII compared to PSI was detrimental to the recovery
of PSI or even to the whole photosystem. 相似文献
13.
We have identified two types of invertases, one bound ionically and the other covalently to the particulate fraction in grains
of heat tolerant C 306 and heat susceptible WH 542 cultivars of wheat (Triticum aestivum L.). The cell walls contained a high level of invertase activity, of which 79.2–72.8% was extractable by 2 M NaCl and 14.9–21.1%
by 0.5% EDTA in C 306 and WH 542, respectively. The NaCl-released invertase constituted the predominant fraction. Using 5–100 mM
sucrose and pH range of 4.0–7.0, the apparent Michaelis constant (K
m, enzyme substrate affinity measure) of enzyme ranged from 5.73 to 16.06 mM for C 306 and from 6.08 to 19.86 mM for WH 542.
The V
max (maximum catalytic rate) values at these pH were higher in C 306 (0.63–11.04 μg sucrose hydrolysed min−1) than WH 542 (0.51–8.73 μg sucrose hydrolysed min−1). By employing photo-oxidation and by studying the effect of pH on K
m and V
max, the involvement of histidine and α-carboxyl groups at the active site of the enzyme was indicated. The two cultivars also
showed differential response in terms of thermodynamic properties of the enzyme i.e. energy of activation (E
a), enthalpy change (ΔH) and entropy change (ΔS). NaCl-released invertase showed differential response to metal ions in two cultivars suggesting their distinctive nature.
Mn2+, Cu2+, Hg2+, Mg2+, Zn2+ and Cd2+ were strong inhibitors in WH 542 as compared to C 306 while K+, Ca2+ were stimulators in both the cultivars. Overall the results suggest that genetic differences exist in wall bound invertase
properties of wheat grains as evident in its altered kinetic behaviour. 相似文献
14.
Copper (II) complex of formulation [Cu–Phen–Tyr](H2O)](ClO4) (Phen = 1,10-phenanthroline, l-Tyr = l-tyrosine), has been prepared, and their induced DNA oxidative cleavage activity studied. The complex binds to DNA by intercalation,
as deduced from the absorption and fluorescence spectral data. Scatchard plots constructed from the absorption titration data
gave binding constant 2.44 × 104 M−1 of base pairs. Extensive hypochromism, broadening, and red shifts in the absorption spectra were observed. Upon binding to
DNA, the fluorescence from the DNA–ethidium bromide system was efficiently quenched by the copper (II) complex. Stern–Volmer
quenching constant 0.61 × 103 M−1 obtained from the linear quenching plots. [Cu–Phen–Tyr] complex efficiently cleave the supercoiled DNA to its nicked circular
form with gallic acid as biological reductant at appropriate complex concentration. The gallic acid as reductant could observably
improve copper (II) complex to DNA damage. The pseudo-Michaelis–Menten kinetic parameters (k
cat, K
M) were calculated to be 1.32 h−1 and 5.46 × 10−5 M for [Cu–Phen–Tyr] complex. Mechanistic studies reveal the involvement of superoxide anions and hydroxyl radical (HO·) as the reactive species under an aerobic medium. 相似文献
15.
《Journal of molecular recognition : JMR》2017,30(6)
The interaction of a recently certified kinase inhibitor Tofacitinib (TFB) with bovine serum albumin (BSA) has been studied, by spectroscopic and molecular docking studies. Spectrofluorimetric measurements at 3 different temperatures (288, 298, and 310 K) showed that TFB quench the intrinsic fluorescence of BSA upon forming a nonfluorescent complex. The intrinsic fluorescence data showed that TFB binds to BSA with binding constant (K b) of approximately 104M−1, affirming a significant affinity of TFB with BSA. The decrease in Stern‐Volmer quenching constant with increasing temperature exhibited the static mechanism of quenching. Negative value of ΔG (−6.94 ± 0.32 kcal·mol−1), ΔH (−7.87 ± 0.52 kcal·mol−1), and ΔS (−3.14 ± 0.42 cal·mol−1·K−1) at all 3 temperatures declared the reaction between BSA and TFB to be spontaneous and exothermic. Far‐UV circular dichroism spectroscopy results demonstrated an increase in helical content of BSA in the presence of TFB. Moreover, dynamic light scattering measurements showed that TFB resulted into a decrease in the hydrodynamic radii (from 3.6 ± 0.053 to 2.9 ± 0.02 nm) of BSA. Molecular docking studies confirmed that TFB binds near site II on BSA, hydrogen bonding, and hydrophobic interaction were involved in the BSA‐TFB complex formation. The present study characterizing the BSA‐TFB interaction could be significant towards gaining an insight into the drug pharmacokinetics and pharmacodynamics and also in the direction of rational drug designing with better competence, against emerging immune‐mediated diseases, ie, alopecia and rheumatoid arthritis. 相似文献
16.
Luz Allende Guillermo Tell Horacio Zagarese Ana Torremorell Gonzalo Pérez José Bustingorry Roberto Escaray Irina Izaguirre 《Hydrobiologia》2009,624(1):45-60
Shallow lakes often alternate between two possible states: one clear with submerged macrophytes, and another one turbid, dominated
by phytoplankton. A third type of shallow lakes, the inorganic turbid, result from high contents of suspended inorganic material,
and is characterized by low phytoplankton biomass and macrophytes absence. In our survey, the structure and photosynthetic
properties (based on 14C method) of phytoplankton were related to environmental conditions in these three types of lakes in the Pampa Plain. The
underwater light climate was characterized. Clear-vegetated lakes were more transparent (K
d 4.5–7.7 m−1), had high DOC concentrations (>45 mg l−1), low phytoplankton Chl a (1.6–2.7 μg l−1) dominated by nanoflagellates. Phytoplankton productivity and photosynthetic efficiency (α ~ 0.03 mgC mgChla
−1 h−1 W−1 m2) were relatively low. Inorganic-turbid lakes showed highest K
d values (59.8–61.4 m−1), lowest phytoplankton densities (dominated by Bacillariophyta), and Chl a ranged from 14.6 to 18.3 μg l−1. Phytoplankton-turbid lakes showed, in general, high K
d (4.9–58.5 m−1) due to their high phytoplankton abundances. These lakes exhibited the highest Chl a values (14.2–125.7 μg l−1), and the highest productivities and efficiencies (maximum 0.56 mgC mgChla
−1 h−1 W−1 m2). Autotrophic picoplankton abundance, dominated by ficocianine-rich picocyanobacteria, differed among the shallow lakes independently
of their type (0.086 × 105–41.7 × 105 cells ml−1). This article provides a complete characterization of phytoplankton structure (all size fractions), and primary production
of the three types of lakes from the Pampa Plain, one of the richest areas in shallow lakes from South America.
Handling editor: J. Padisak 相似文献
17.
Molecular characterization of phenylalanine ammonia lyase gene from <Emphasis Type="Italic">Cistanche deserticola</Emphasis> 总被引:1,自引:0,他引:1
Hu GS Jia JM Hur YJ Chung YS Lee JH Yun DJ Chung WS Yi GH Kim TH Kim DH 《Molecular biology reports》2011,38(6):3741-3750
We cloned the gene, CdPAL1, from Cistanche deserticola callus using RACE PCR with degenerate primers that were designed based on a multiple sequence alignment of known PAL genes
from other plant species. The gene shows high homology to other known PAL genes registered in GenBank. The recombinant protein
exhibited Michaelis–Menten kinetics with a K
m of 0.1013 mM, V
max of 4.858 μmol min−1, K
cat of 3.36 S−1, and K
cat/K
m is 33,168 M−1 S−1. The enzyme had an optimal pH of 8.5 and an activation energy of 38.92 kJ mol−1 when l-Phenylalanine was used as a substrate; l-tyrosine cannot be used as substrate for this protein. The optimal temperature was 55°C, and the thermal stability results
showed that, after a treatment at 70°C for 20 min, the protein retained 87% activity, while a treatment at 75°C for 20 min
resulted in a loss of over 85% of the enzyme activity. Treatment with heavy metal ions (Hg2+, Pb2+, and Zn2+) showed remarkable inhibitory effects. Among the intermediates from the lignin (cinnamyl alcohol, cinnamyl aldehyde, coniferyl
aldehyde, coniferyl alcohol), phenylpropanoid (cinnamic acid, coumaric acid, caffeic acid, and chlorogenic acid) and phenylethanoid
(tyrosol and salidroside) biosynthetic pathways, only cinnamic acid showed strong inhibitory effects against CdPAL1 activity with a K
i of 8 μM. Competitive inhibitor AIP exhibited potent inhibition with K
i = 0.056 μM. 相似文献
18.
Lipase-catalyzed synthesis of isoamyl acetate in hexane at 10–250 MPa at 80°C and 1–100 MPa at 40°C resulted in activation
volumes of −12.9 ± 1.7 and −21.6 ± 2.9 cm3 mol−1, respectively. Increasing pressure from 10 to 200 MPa resulted in approximately 10-fold increase in V
max at both 40 and 80°C. Pressure increased the K
m from 2.4 ± 0.004 to 38 ± 0.78 mM at 40°C. In contrast, at 80°C the pressure did not affect the K
m. 相似文献
19.
In this work, fluorescence spectroscopy in combination with circular dichroism spectroscopy and molecular modeling was employed
to investigate the binding of 10-hydroxycamptothecin (HCPT) to human serum albumin (HSA) under simulative physiological conditions.
The experiment results showed that the fluorescence quenching of HSA by HCPT was a result of the formation of HCPT–HSA complex.
The corresponding association constants (K
a) between HCPT and HSA at four different temperatures were determined according to the modified Stern–Volmer equation. The
results of thermodynamic parameters ΔG, ΔH, and ΔS indicated that hydrogen bonds and van der Waals forces played major roles for HCPT–HSA association. Site marker competitive
displacement experiment indicated that the binding of HCPT to HSA primarily took place in sub-domain IIA (site I). Molecular
docking study further confirmed the binding mode and the binding site obtained by fluorescence and site marker competitive
experiments. The conformational investigation showed that the presence of HCPT decreased the α-helical content of HSA and
induced the slight unfolding of the polypeptides of protein, which confirmed some micro-environmental and conformational changes
of HSA molecules. 相似文献
20.
Hiroshi Takashima Ayako Araki Keiko Takemoto Naokazu Yoshikawa Keiichi Tsukahara 《Journal of biological inorganic chemistry》2006,11(3):316-324
In order to understand the detailed mechanism of the stereoselective photoinduced electron-transfer (ET) reactions of zinc-substituted
myoglobin (ZnMb) with optically active molecules by flash photolysis, we designed and prepared new optically active agents,
such as N,N′-dimethylcinchoninium diiodide ([MCN]I2) and N,N′-dimethylcinchonidinium diiodide ([MCD]I2). The photoexcited triplet state of ZnMb, 3(ZnMb)*, was successfully quenched by [MCN]2+ and [MCD]2+ ions to form the radical pair of ZnMb cation (ZnMb·+) and reduced [MCN]·+ and [MCD]·+, followed by a thermal back ET reaction to the ground state. The rate constants (k
q) for the ET quenching at 25 °C were obtained as k
q(MCN)=(1.9±0.1)×106 M−1 s−1 and k
q(MCD)=(3.0±0.2)×106 M−1 s−1, respectively. The ratio of k
q(MCD)/k
q(MCN)=1.6 indicates that the [MCD]2+ preferentially quenches 3(ZnMb)*. The second-order rate constants (k
b) for the thermal back ET reaction from [MCN]·+ and [MCD]·+ to ZnMb·+ at 25 °C were k
b(MCN)=(0.79±0.04)×108 M−1 s−1 and k
b(MCD)=(1.0±0.1)×108 M−1 s−1, respectively, and the selectivity was k
q(MCD)/k
q(MCN)=1.3. Both quenching and thermal back ET reactions are controlled by the ET step. In the quenching reaction, the energy
differences of ΔΔH
≠(MCD–MCN) and ΔΔS
≠(MCD–MCN) at 25 °C were obtained as −1.1 and 0 kJ mol−1, respectively. On the other hand, ΔΔH
≠(MCD–MCN)=11±2 kJ mol−1 and TΔΔS
≠(MCD–MCN)=−10±2 kJ mol−1 were given in the thermal back ET reaction. The highest stereoselectivity of 1.7 for [MCD]·+ found at low temperature (10 °C) was due to the ΔΔS
≠ value obtained in the thermal back ET reaction.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献