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1.
From a heterotrophic bacterium,Xanthomonas sp. DY44 which was previously reported to oxidize hydrogen sulfide (H2S) to polysulfide, cytochromec-555 (cyt.c-555) responsible for oxidation of sulfide was purified by DEAE-Toyopearl and Sepadex G-75 column chromatography. Cyt.c-555 with a molecular weight of 12,500 showed maximum absorption at 555 nm (α-peak), 522 nm (β-peak) and 417 nm (γ-peak) for
the reduced form which was prepared by addition of Na2S2O4. Cyt.c-555 was also reduced by addition of sulfide (Na2S and H2S), and the oxidized products of sulfide by cyt.c-555 was identified as polysulfide. The reduced form of cyt.c-555 was suggested to be oxidized coupled with cyt.c oxidase which is tolerant to sulfide. 相似文献
2.
Nanosilver of 10-nm size was prepared by the NaBH4–sodium citrate procedure, and it was modified by a single-strand DNA (ssDNA) aptamer to fabricate an AgssDNA probe for melamine.
The probe was stabile at pH 7.0 Na2HPO4–NaH2PO4 buffer solutions and in the presence of 25.0 mmol/L NaCl. Upon the addition of melamine, it interacted with the probe to
aggregate big clusters, which led to the resonance scattering (RS) intensity at 470 nm increasing greatly. Under the selected
conditions, the increased RS intensity (ΔI
470 nm) is linear to melamine concentration in the range of 6.31–378.4 μg/L, with a regression equation of DI470 nm = 1.124c + 10.8 \Delta {I_{{47}0{\rm{ nm}}}} = {1}.{124}c + { 10}.{8} and a detection limit of 3.1 μg/L. The aptamer-modified nanosilver RS assay has been applied for the determination of melamine
in milk, with satisfactory results. 相似文献
3.
Amit Jaiswal Pallab Sanpui Arun Chattopadhyay Siddhartha Sankar Ghosh 《Plasmonics (Norwell, Mass.)》2011,6(1):125-132
Water dispersible zinc sulfide quantum dots (ZnS QDs) with an average diameter of 2.9 nm were synthesized in an environment
friendly method using chitosan as stabilizing agent. These nanocrystals displayed characteristic absorption and emission spectra
having an absorbance edge at 300 nm and emission maxima (λ
emission) at 427 nm. Citrate-capped silver nanoparticles (Ag NPs) of ca. 37-nm diameter were prepared by modified Turkevich process.
The fluorescence of ZnS QDs was significantly quenched in presence of Ag NPs in a concentration-dependent manner with K
sv value of 9 × 109 M−1. The quenching mechanism was analyzed using Stern–Volmer plot which indicated mixed nature of quenching. Static mechanism
was evident from the formation of electrostatic complex between positively charged ZnS QDs and negatively charged Ag NPs as
confirmed by absorbance study. Due to excellent overlap between ZnS QDs emission and surface plasmon resonance band of Ag
NPs, the role of energy transfer process as an additional quenching mechanism was investigated by time-resolved fluorescence
measurements. Time-correlated single-photon counting study demonstrated decrease in average lifetime of ZnS QDs fluorescence
in presence of Ag NPs. The corresponding F?rster distance for the present QD–NP pair was calculated to be 18.4 nm. 相似文献
4.
The light-induced difference absorption spectra associated to the photo-accumulation of reduced pheophytin a were studied in the isolated D1–D2–Cyt b559 complex in the presence of variable methyl viologen concentrations and different illumination conditions under anaerobiosis.
Depending on the methyl viologen/reaction centre ratio, the relative intensities of the spectral bands at 681.5±0.5, 667.0±0.5
and 542.5±0.5 nm were modified. The reduced pheophytin a located at the D1-branch of the complex absorbs at 681.7±0.5 nm, and at least two additional pigment species contribute to
the Qy band of the difference absorption spectra with maxima at 667.0±0.5 and 680.5±0.5 nm. We propose the additional species correspond
to a peripheral chlorophyll a and the pheophytin a located at the D2-branch of the complex, respectively. The blue absorbing chlorophyll at 667 nm is susceptible to chemical
redox changes with a midpoint reduction potential of +470 mV. The Qx absorption bands of both pheophytins localised at the D2- and D1-branch of the D1–D2–Cyt b559 complex were at 540.7±0.5 and 542.9±0.5, respectively. The results indicated that the two pheophytin molecules can be
photoreduced in the D1–D2–Cyt b559 complex in certain experimental conditions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
Roberto E. Di Paolo Patrícia M. Pereira Inês Gomes Filipa M. A. Valente Inês A. C. Pereira Ricardo Franco 《Journal of biological inorganic chemistry》2006,11(2):217-224
Resonance Raman (RR) spectroscopy was used to investigate conformational characteristics of the hemes of several ferricytochromes
of the cytochrome c
3 family, electron transfer proteins isolated from the periplasm and membranes of sulfate-reducing bacteria. Our analysis concentrated
on the low-frequency region of the RR spectra, a fingerprint region that includes vibrations for heme-protein C–S bonds [ν(CaS)]. It has been proposed that these bonds are directly involved in the electron transfer process. The three groups of tetraheme
cytochrome c
3 analyzed, namely Type I cytochrome c
3 (TpIc
3s), Type II cytochrome c
3 (TpIIc
3s) and Desulfomicrobium cytochromes c
3, display different frequency separations for the two ν(CaS) lines that are similar among members of each group. These spectral differences correlate with differences in protein structure
observed among the three groups of cytochromes c
3. Two larger cytochromes of the cytochrome c
3 family display RR spectral characteristics for the ν(CaS) lines that are closer to TpIIc
3 than to TpIc
3. Two other multiheme cytochromes from Desulfovibrio that do not belong to the cytochrome c
3 family display ν(CaS) lines with reverse relative areas in comparison with the latter family. This RR study shows that the small differences
in protein structure observed among these cytochrome c
3 correlate to differences on the heme–protein bonds, which are likely to have an impact upon the protein function, making
RR spectroscopy a sensitive and useful tool for characterizing these cytochromes. 相似文献
6.
Planktonic nitrate-reducing bacteria and sulfate-reducing bacteria in some western Canadian oil field waters 总被引:3,自引:0,他引:3
Oil fields that use water flooding to enhance oil recovery may become sour because of the production of H2S from the reduction of sulfate by sulfate-reducing bacteria (SRB). The addition of nitrate to produced waters can stimulate
the activities of nitrate-reducing bacteria (NRB) and control sulfide production. Many previous studies have focused on chemolithotrophic
bacteria that can use thiosulfate or sulfide as energy sources while reducing nitrate. Little attention has been given to
heterotrophic NRB in oil field waters. Three different media were used in this study to enumerate various types of planktonic
NRB present in waters from five oil fields in western Canada. The numbers of planktonic SRB and bacteria capable of growth
under aerobic conditions were also determined. In general, microbial numbers in the produced waters were very low (<10 ml−1) in samples taken near or at wellheads. However, the numbers increased in the aboveground facilities. No thiosulfate-oxidizing
NRB were detected in the oil field waters, but other types of NRB were detected in 16 of 18 produced water samples. The numbers
of heterotrophic NRB were equal to or greater than the number of sulfide-oxidizing, chemolithotrophic NRB in 12 of 15 samples.
These results showed that each of the oil fields contained NRB, which might be stimulated by nitrate amendment to control
H2S production by SRB. Journal of Industrial Microbiology & Biotechnology (2002) 29, 83–92 doi:10.1038/sj.jim.7000274
Received 20 February 2002/ Accepted in revised form 14 May 2002 相似文献
7.
Günter A. Peschek 《BBA》1981,635(3):470-475
The cytochrome content of membrane fragments prepared from the bluegreen alga (cyanobacterium) Anacystis nidulans was examined by difference spectrophotometry. Two b-type cytochromes and a hitherto unknown cytochrome a could be characterized. In the reduced-minus-oxidised difference spectra the a-type cytochrome showed an α-band at 605 nm and a γ-band at 445 nm. These bands shifted to 590 and 430 nm, respectively, in CO difference spectra. NADPH, NADH and ascorbate reduced the cytochrome through added horse heart cytochrome c as electron mediator. In presence of KCN the reduced-minus-oxidised spectrum showed a peak at 600 nm and a trough at 604 nm. Photoaction spectra of O2 uptake and of horse heart cytochrome c oxidation by CO-inhibited membranes showed peaks at 590 and 430 nm. These findings are consistent with cytochrome aa3 being the predominant respiratory cytochrome c oxidase in Anacystis nidulans. 相似文献
8.
Patrizia Bonora Ilaria Principi Alejandro Hochkoeppler Roberto Borghese D. Zannoni 《Archives of microbiology》1998,170(6):435-441
The halophilic purple nonsulfur bacterium Rhodospirillum sodomense has been previously described as an obligate phototroph that requires yeast extract and a limited number of organic compounds
for photoheterotrophic growth. In this work, we report on chemoheterotrophic growth of R. sodomense in media containing either acetate or succinate supplemented with 0.3–0.5% yeast extract. Plasma membranes isolated from
cells grown aerobically in the dark contained three b-type and three c-type membrane-bound cytochromes with E
m,7 of +171 ± 10, +62 ± 10 and –45 ± 13 mV (561–575 nm), and +268 ± 6, +137 ± 10 and –43 ± 12 mV (551–540 nm). A small amount
of a soluble c-type cytochrome with a mol. mass of 15 kDa (E
m,7≥ +150 mV) was identified. Spectroscopic and immunological methods excluded the presence of cytochrome of the c
2
class and high-potential iron-sulfur proteins. Inhibitory studies indicated that only 60–70% of the respiratory activity
was blocked by low concentrations of cyanide, antimycin A, and myxothiazol (10, 0.1, and 0.2 μM, respectively). These results
were interpreted to show that the oxidative electron transport chain of R. sodomense is branched, leads to a quinol oxidase that is fully blocked by 1 mM cyanide and that is involved in light-dependent oxygen
reduction, and leads to a cytochrome c oxidase that is inhibited by 10 μM cyanide. These features taken together suggest that R. sodomense differs from the closely related species Rhodospirillum salinarum and from other species of the genus Rhodospirillum in that it contains multiple membrane-bound cytochromes c.
Received: 8 June 1998 / Accepted: 25 August 1998 相似文献
9.
The rabbit Na+/glucose cotransporter (SGLT1) exhibits a presteady-state current after step changes in membrane voltage in the absence of
sugar. These currents reflect voltage-dependent processes involved in cotransport, and provide insight on the partial reactions
of the transport cycle. SGLT1 presteady-state currents were studied as a function of external Na+, membrane voltage V
m
, phlorizin and temperature. Step changes in membrane voltage—from the holding V
h
to test values, elicited transient currents that rose rapidly to a peak (at 3–4 msec), before decaying to the steady state,
with time constants τ≈4–20 msec, and were blocked by phlorizin (K
i
≈30 μm). The total charge Q was equal for the application of the voltage pulse and the subsequent removal, and was a function of V
m
. The Q-V curves obeyed the Boltzmann relation: the maximal charge Q
max was 4–120 nC; V
0.5, the voltage for 50% Q
max was −5 to +30 mV; and z, the apparent valence of the moveable charge, was 1. Q
max and z were independent of V
h
(between 0 and −100 mV) and temperature (20–30°C), while increasing temperature shifted V
0.5 towards more negative values. Decreasing [Na+]
o
decreased Q
max, and shifted V
0.5 to more negative voltages 9by −100 mV per 10-fold decrease in [Na+]
o
). The time constant τ was voltage dependent: the τ-V relations were bell-shaped, with maximal τmax 8–20 msec. Decreasing [Na+]
o
decreased τmax, and shifted the τ-V curves towards more negative voltages. Increasing temperature also shifted the τ-V curves, but did not affect τmax. The maximum temperature coefficient Q
10 for τ was 3–4, and corresponds to an activation energy of 25 kcal/mole. Simulations of a 6-state ordered kinetic model for
rabbit Na+/glucose cotransport indicate that charge-movements are due to Na+-binding/dissociation and a conformational change of the empty transporter. The model predicts that (i) transient currents
rise to a peak before decay to steady-state; (ii) the τ-V relations are bell-shaped, and shift towards more negative voltages as [Na+]
o
is reduced; (iii) τmax is decreased with decreasing [Na+]
o
; and (iv) the Q-V relations are shifted towards negative voltages as [Na+]
o
is reduced. In general, the kinetic properties of the presteady-state currents are qualitatively predicted by the model.
Received: 12 August 1996/Revised: 30 September 1996 相似文献
10.
Ivanova EP Hasan J Truong VK Wang JY Raveggi M Fluke C Crawford RJ 《Applied microbiology and biotechnology》2011,91(4):1149-1157
The physicochemical and bactericidal properties of thin silver films have been analysed. Silver films of 3 and 150 nm thicknesses
were fabricated using a magnetron sputtering thin-film deposition system. X-ray photoelectron and energy dispersive X-ray
spectroscopy and atomic force microscopy analyses confirmed that the resulting surfaces were homogeneous, and that silver
was the most abundant element present on both surfaces, being 45 and 53 at.% on the 3- and 150-nm films, respectively. Inductively
coupled plasma time of flight mass spectroscopy (ICP-TOF-MS) was used to measure the concentration of silver ions released
from these films. Concentrations of 0.9 and 5.2 ppb were detected for the 3- and 150-nm films, respectively. The surface wettability
of the films remained nearly identical for both film thicknesses, displaying a static water contact angle of 95°, while the
surface free energy of the 150-nm film was found to be slightly greater than that of the 3-nm film, being 28.8 and 23.9 mN m−1, respectively. The two silver film thicknesses exhibited statistically significant differences in surface topographic profiles
on the nanoscopic scale, with R
a, R
q and R
max values of 1.4, 1.8 and 15.4 nm for the 3-nm film and 0.8, 1.2 and 10.7 nm for the 150-nm film over a 5 × 5 μm scanning area.
Confocal scanning laser microscopy and scanning electron microscopy revealed that the bactericidal activity of the 3-nm silver
film was not significant, whereas the nanoscopically smoother 150-nm silver film exhibited appreciable bactericidal activity
towards Pseudomonas aeruginosa ATCC 9027 cells and Staphylococcus aureus CIP 65.8 cells, obtaining up to 75% and 27% sterilisation effect, respectively. 相似文献
11.
Giovanni Moschettini Alejandro Hochkoeppler Barbara Monti Bruna Benelli D. Zannoni 《Archives of microbiology》1997,168(4):302-309
Plasma membranes isolated from cells of the halophilic purple nonsulfur bacterium Rhodospirillum salinarum grown in light or in the dark were examined. Membranes isolated from cells grown aerobically in the dark contained three
b-type and two c-type membrane-bound cytochromes with E
m,7 of +180, +72 and –5 mV (561–575 nm), and +244 and +27 mV (551–540 nm), respectively. Conversely, membranes isolated from
cells grown anaerobically in the light contained two b-type and five c-type haems with E
m,7 of +60 and –45 mV and +290, +250, +135, –20 and –105 mV, respectively. In addition to haems of the b- and c-type, two haems of the a-type (E
m,7 of +325 and +175 mV) were present only in cells grown in the dark. Four soluble cytochromes of the c type, but not cytochrome c
2, along with two high-potential iron-sulfur proteins (HiPIP iso-1 and iso-2) were also identified in cells grown aerobically.
Inhibitory studies showed that 85–90% of the respiratory activity was blocked by very low concentrations of cyanide, antimycin
A and myxothiazol (50, 0.1 and 0.2 mM, respectively). These results taken together were interpreted to show that the oxidative
electron transport chain of Rsp. salinarum is linear, leading to a membrane-bound oxidase of the aa
3 type in cells grown in the dark, while no significant cytochrome oxidase activity is catalyzed by photosynthetic membranes.
These features suggest that this halophilic species is unique among the genus Rhodospirillum and that it also differs from other facultative phototrophs (e.g., Rhodobacter species) in that it does not contain either cytochrome c
2 or a branched respiratory chain.
Received: 25 February 1997 / Accepted: 20 May 1997 相似文献
12.
J. M. Visser Govardus A. H. de Jong L. A. Robertson J. Gijs Kuenen 《Archives of microbiology》1997,167(5):295-301
A novel membrane-bound sulfide-oxidizing enzyme was purified 102-fold from the neutrophilic, obligately chemolithoautotrophic
Thiobacillus sp. W5 by means of a six-step procedure. Spectral analysis revealed that the enzyme contains haem c and flavin. SDS-PAGE showed the presence of two types of subunit with molecular masses of 40 and 11 kDa. The smaller subunit
contains covalently bound haem c, as was shown by haem staining. A combination of spectral analysis and the pyridine haemochrome test indicated that the sulfide-oxidizing
heterodimer contains one molecule of haem c and one molecule of flavin. It appeared that the sulfide-oxidizing enzyme is a
member of a small class of redox proteins, the flavocytochromes c, and is structurally most related to the flavocytochrome c sulfide dehydrogenase of the green sulfur bacterium Chlorobium limicola. The pH optimum of the enzyme is 8.6. At pH 9, the V
max was 2.1 ± 0.1 μmol cytochrome c (mg protein)–1 min–1, and the K
m values for sulfide and cytochrome c were 1.7 ± 0.4 μM and 3.8 ± 0.8 μM, respectively. Cyanide inhibited the enzyme by the formation of an N-5 adduct with the
flavin moiety of the protein. On the basis of electron transfer stoichiometry, it seems likely that sulfur is the oxidation
product.
Received: 15 October 1996 / Accepted: 7 January 1997 相似文献
13.
The purpose of this study was to formulate drug-loaded polyelectrolyte matrices constituting blends of pectin, chitosan (CHT)
and hydrolyzed polyacrylamide (HPAAm) for controlling the premature solvation of the polymers and modulating drug release.
The model drug employed was the highly water-soluble antihistamine, diphenhydramine HCl (DPH). Polyelectrolyte complex formation
was validated by infrared spectroscopy. Matrices were characterized by textural profiling, porositometry and SEM. Drug release
studies were performed under simulated gastrointestinal conditions using USP apparatus 3. FTIR spectra revealed distinctive
peaks indicating the presence of –COO− symmetrical stretching (1,425–1,390 cm−1) and -NH3+ deformation (1,535 cm−1) with evidence of electrostatic interaction between the cationic CHT and anionic HPAAm corroborated by molecular mechanics
simulations of the complexes. Pectin–HPAAm matrices showed electrostatic attraction due to residual –NH2 and –COO− groups of HPAAm and pectin, respectively. Textural profiling demonstrated that CHT-HPAAm matrices were most resilient at
6.1% and pectin–CHT–HPAAm matrices were the least (3.9%). Matrix hardness and deformation energy followed similar behavior.
Pectin–CHT–HPAAm and CHT–HPAAm matrices produced type IV isotherms with H3 hysteresis and mesopores (22.46 nm) while pectin–HPAAm
matrices were atypical with hysteresis at a low P/P0 and pore sizes of 5.15 nm and a large surface area. At t
2 h, no DPH was released from CHT–HPAAm matrices, whereas 28.2% and 82.2% was released from pectin–HPAAm and pectin–CHT–HPAAm
matrices, respectively. At t
4 h, complete DPH release was achieved from pectin–CHT–HPAAm matrices in contrast to only 35% from CHT–HPAAm matrices. This revealed
the release-modulating capability of each matrix signifying their applicability in controlled oral drug delivery applications. 相似文献
14.
Proton transport in the terminal part of the respiratory chain in the extremely alkaliphilic halotolerant bacterial strain Thioalkalivibrio versutus was studied under near-optimum growth conditions (pH 9.0-9.5). Under these conditions, bacterial cells generated electric potential with the negative charge being inside the cells. When only the terminal part of the respiratory chain functioned, it was found that: 1) unlike other bacteria known, this bacterium did not acidify the medium in the presence of K+ and valinomycin; 2) in the presence of an uncoupler, CCCP, but in the absence of valinomycin, reversible alkalinization of the medium occurred as a result of proton influx into the cells. Cyanide prevented this alkalinization. The difference spectra indicate that cell membranes contained cytochromes c and (b + o), some of which reacted with CO. The respiratory activity of membranes in the terminal part of the respiratory chain was optimal at pH 9.5 and specifically depended on sodium ions (C
1/2 = 10 mM). The data suggest the presence of a Na+-pump in the terminal part of the respiratory chain of the studied strain which can pump Na+ out of the cells. 相似文献
15.
The clastogenic effect ofN-methyl-N′-nitro-N-nitrosoguanidine (MNNG) in Chinese hamster ovary (CHO) cells and its modulation by Na2SeO3 and caffeine were studied by metaphase analysis of chromosome aberrations (CA) as well as by measuring the formation and
repair of single-strand (ss) DNA breaks employing hydroxylapatite chromatography. Treatment of CHO cells with MNNG (1.25 or
2.5 × 10-5M) for 3 h caused CA in 11 and 19% of metaphases scored, respectively. Pretreatment of cells with Na2SeO3 (1–5 μg/mL) or caffeine (0.2–2.0 mg/mL) for 2 h resulted in a 2–3.5-fold increase of CA frequency. Addition of both modulators
during the mutagen exposure tended to cause a slight inhibition of clastogenic activity of MNNG (1.25 × 10−5
M) or had no effect on CA number when MNNG was used at a concentration of 2.5 × 10−5M. Posttreatment of CHO cells with Na2SeO3 for 20 h after MNNG was ineffective in influencing the number of metaphases with CA, whereas, at these conditions, caffeine
enhanced up to 6-7-fold the clastogenic activity of MNNG. Addition of both modulators during the whole experiment, 2 h pretreatment
included, resulted in a further significant increase of CA frequency up to the total pulverization of chromosomes in all metaphases
scored. The coclastogenic effect of caffeine was greater in this case. The enhancement of chromosome-damaging activity of
MNNG by selenite and caffeine was better expressed when this carcinogen was applied at the higher concentration used. An additive
coclastogenic effect was observed in CHO cells treated simultaneously with Na2SeO3 and caffeine plus MNNG. In addition, the treatment of CHO cells with MNNG (5 × 10−6
M) caused a rapid increase of ssDNA breaks number reaching maximal values after 30–45 min. However, up to 50–60% of MNNG-induced
ssDNA breaks were repaired during the first 60–150 min after the mutagen exposure. The 2 h pretreatment of CHO cells with
Na2SeO3 (2 μg/mL) or the addition of this trace element after MNNG had no effect on formation and repair of MNNG-induced ssDNA breaks.
The coclastogenic effect of Na2SeO3 in CHO cells treated with MNNG was not directly linked to the induction and disappearance of ssDNA breaks measured by hydroxylapatite
chromatography. 相似文献
16.
FTIR-spectral analysis of two photosynthetic H2-producing strains and their extracellular polymeric substances 总被引:2,自引:0,他引:2
The Fourier transform infrared (FTIR) spectra of the cells of two photosynthetic H2-producing strains, Rhodoblastus acidophilus and Rhodobacter capsulatus, as well as their extracellular polymeric substances (EPS), were evaluated. The FTIR spectra of R.
capsulatus and its EPS during its cultivation were also recorded. The main peaks in the spectra, including 1,080 cm−1 (carbohydrates), 1,250 cm−1 (nucleic acids), 2,830–2,930 cm−1 (lipids), 1,660–1,535 cm−1 (Amide I and II of proteins), were observed. The relative heights of these peaks in the spectra of the two strains were different, showing the difference in contents of various components in the cells or EPS. The ratios among the main components in the EPS obtained from the FTIR spectra were in good agreement with those from a conventional quantitative chemical analysis. As an easy, rapid, and direct technique, the FTIR spectroscopy could be used to characterize the components and their relative contents of EPS of photosynthetic bacteria.An erratum to this article can be found at 相似文献
17.
Scutellarin (Scu), the main bioactive component of Erilgeron breviscapus, protects the brain against ischemic damages. To explore the therapeutic mechanism of Scu, we investigated the impact of
Scu on sodium current (I
Na) of freshly isolated mouse hippocampal CA1 neurons using the whole-cell patch clamp technique. Results showed that Scu inhibited
I
Na in concentration- and holding potential-dependent manners. At 50 μM, Scu markedly shifted the steady state inactivation curve
of I
Na towards a more negative potential, slowed down the recovery of I
Na from inactivation state, and elicited a frequency-dependent block of I
Na. The shape of the current–voltage (I–V) curve and the steady state activation curve of I
Na were unaffected by Scu treatment. These findings suggest that Scu is capable of inhibiting I
Na in neurons through predominantly affecting the inactivated state of I
Na. Inhibition of Na+ channels provides a novel pharmacological basis for the anti-ischemic application of Scu. 相似文献
18.
Yeast cytochrome P-450 catalyzing lanosterol 14 alpha-demethylation. I. Purification and spectral properties 总被引:4,自引:0,他引:4
A form of cytochrome P-450 catalyzing lanosterol 14 alpha-demethylation (tentatively called "P-450(14)DM") was purified from microsomes of semi-anaerobically grown cells of Saccharomyces cerevisiae to gel electrophoretic homogeneity. An apparent monomeric Mr = 58,000 was estimated for the purified cytochrome by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Both optical and EPR spectra of oxidized P-450(14)DM are characteristic of low spin ferric heme proteins, and its reduced CO complex showed a Soret absorption peak at 447 nm. As in the case of hepatic microsomal cytochromes P-450, the ethyl isocyanide complex of reduced P-450(14)DM was in a pH-dependent equilibrium between two states having Soret peaks at 429 and 453 nm, the equilibrium being considerably shifted toward the 453-nm state. Oxidized P-450(14)DM was peculiar in that in its CD spectrum there was a negative shoulder at 425 nm and the 350- and 414-nm troughs possessed larger and relatively smaller [theta] values, respectively, than those reported for other low spin ferric cytochromes P-450. Lanosterol was the only compound which caused a Type I spectral change in oxidized P-450(14)DM. The lanosterol-induced low to high spin state change was, however, only slight even at saturating concentrations of the sterol, indicating that the lanosterol-P-450(14)DM adduct was in a spin state equilibrium. 相似文献
19.
The uptake of 3H-labeled choline by a suspension of isolated type II epithelial cells from rat lung has been studied in a Ringer medium.
Uptake was linear for 4 min at both 0.1 μm and 5.0 μm medium choline; at 5 μm, only 10% of the label was recovered in a lipid fraction. Further experiments were conducted at the low concentration (0.1
μm), permitting characterization of the properties of high-affinity systems. Three fractions of choline uptake were detected:
(i) a sodium-dependent system that was totally inhibited by hemicholinium-3 (HC-3); (ii) a sodium-independent uptake, when
Na+ was replaced by Li+, K+ or Mg2+, inhibited by HC-3; (iii) a residual portion persisting in the absence of Na+ and unaffected by HC-3. Choline uptake was sigmoidally related to the medium Na+ concentration. Kinetic properties of the uptake of 0.1 μm
3H-choline in the presence and absence of medium Na+ were examined in two ways. (a) Inhibition by increasing concentrations of unlabeled choline (0.5–100 μm) was consistent with the presence of two Michaelis-Menten-type systems in the presence of Na+; a Na+-dependent portion (a mean of 0.52 of the total) had a K
m
for choline of 1.5 μm while K
m
in the absence of Na+ (Li+ substituting) was 18.6 μm. (b) Inhibition by HC-3 (0.3–300 μm) gave Ki values of 1.7 μm and 5.0 μm HC-3 for the Na+-dependent and -independent fractions. The apparent K
m
of the Na+-dependent uptake is lower than that reported previously for lung-derived cells and is in the range of the K
m
values reported for high-affinity, Na+-dependent choline uptake by neuronal cells.
Received: 18 February 1997/Revised: 7 December 1997 相似文献
20.
Liang A Qin H Zhou L Zhang Y Ouyang H Wang P Jiang Z 《Bioprocess and biosystems engineering》2011,34(5):639-645
In the pH 6.6 Na2HPO4–NaH2PO4 buffer solutions and in the presence of urease catalyst, urea can be decomposed to form NH4
+. The NH4
+ reacted with sodium tetraphenyl boron (NaTPB) to form the association particles that exhibited a resonance scattering (RS)
peak at 474 nm. When the urea concentration increased, NH4
+ increased, and RS intensity at 474 nm enhanced linearly. Under the chosen conditions, the increased RS intensity (ΔI
474 nm) had a linear response to the urea concentration in the range of 0.125–15 μM, with a detection limit of 0.058 μM urea, and
a regression equation of ΔI
474 nm = 31.6C + 2.1, a correlation coefficient of 0.9986. This catalytic RS method was applied for the detection of urea in human serum
sample, with good selectivity and sensitivity, and the results were consistent with the reference method. 相似文献