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1.
The synthesis, spectroscopic, and electrochemical properties of trans-[L(Pyr)(NH3)4RuII/III] (Pyr=py, 3-phpy, 4-phpy, 3-bnpy, or 4-bnpy; L=H2O, Guo, dGuo, 1MeGuo, Gua, Ino, or G7-DNA) are reported. As expected, the Pyr ligand slows DNA binding by trans-[(H2O)(Pyr)(NH3)4RuII]2+ relative to [(H2O)(NH3)5RuII]2+ and favors reduction of RuIII by about 150 mV. The pyridine ligand also promotes the disproportionation of RuIII to afford the corresponding complexes of RuII and, presumably, RuIV. For L=Ino, disproportionation follows the rate law: d[RuII]/dt=k
0[RuIII]+k
1[OH–][RuIII], k
0=(2.7±0.7)×10–4 s–1 and k
1=70±1 M–1 s–1.
Received: 11 May 1998 / Accepted: 3 March 1999 相似文献
2.
A. Mark Dobbing Joo-Yeon Han A. G. Sykes 《Journal of biological inorganic chemistry》1998,3(6):620-626
Dithionite has been found to reduce directly (without mediators) the Escherichia coli R2 subunit of ribonucleotide reductase. With dithionite (∼10 mM) in large excess, the reaction at 25 °C is complete in ∼10 h.
Preparations of E. coli R2 have an FeIII
2 (met-R2) component in this work at ∼40% levels, alongside the fully active enzyme FeIII
2 . . . Tyr*, which has a tyrosyl radical at Tyr-122. In the pH range studied (7–8) the kinetics are biphasic. Rate laws for
both phases give [S2O4
2–] and not [S2O4
2–]1/2 dependencies, and saturation kinetics are observed for the first time in R2 studies. No dependence on pH was detected. The
kinetics (25 °C) of the first phase are reproduced in separate experiments using only met-R2, with association of S2O4
2– to met-R2, K=330 M–1, occurring prior to electron transfer, k
et=4.8×10–4 s–1, I=0.100 M (NaCl). The second phase assigned to the reaction of FeIII
2 . . . Tyr* with S2O4
2– gives K=800 M–1 and k
et=5.6×10–5 s–1. Bearing in mind the substantially smaller reduction potential for FeIII
2 compared to Tyr*, this is a quite remarkable finding, with implications similar to those already reported for the reaction
of R2 with hydrazine, but with additional information provided by the saturation kinetics. The similarity in rates for the
two phases (∼fourfold difference) suggests that reduction of FeIII
2 is occurring in both cases, and since S2O4
2– is involved a two-equivalent change is proposed with the formation of FeII
2 . . . Tyr* in the case of active R2. As a sequel to the second phase, intramolecular reduction of the strongly oxidising
Tyr* by the FeII
2 is rapid, and further decay of FeIIFeIII is also fast. There is no stable mouse met-R2 form, and the single-phase reaction with dithionite gives saturation kinetics
with K=208 M–1 and k
et=1.7±10–3 s–1. Mechanistic implications, including the applicability of a pathway for electron transfer via FeA, are considered.
Received: 25 February 1998 / Received: 20 August 1998 相似文献
3.
A. D. Ryabov Yulia N. Firsova Aleksei Y. Ershov Ilia A. Dementiev 《Journal of biological inorganic chemistry》1999,4(2):175-182
Glucose oxidase-catalyzed reduction of cis[MIII (LL)2Cl2]+ (M=Os and Ru) complexes to cis[MII (LL)2Cl2] (LL=2,2′-bipyridine and 1,10-phenanthroline type ligands) by d-glucose is a first-order process in the complex and the enzyme in aqueous buffered solution. The reaction follows MichaelisMenten
kinetics in d-glucose and the rate is independent of d-glucose concentration above 0.03 M. The reactivity decreases in the series [Ru(bpy)2Cl2]+ > [Os(phen)2Cl2]+ > [Os(4,4′-Me2bpy)2Cl2]+ > [Os(4,7Me2phen)2Cl2]+. The measured second-order rate constant for the oxidation of reduced glucose oxidase by [Os(phen)2Cl2]+ in air equals 1.2×105 M–1 s–1 at pH 6.7, [d-glucose] 0.05 M, and 25 °C, which is ca. 20% less than that when the reaction solutions are purged with argon. In the case
of [Ru(bpy)2Cl2]+ the rate constant equals 1.8×105 M–1 s–1 under similar conditions in air, showing higher reactivity of Ru complexes compared with Os ones. The reduction is pH-dependent
with a maximum around 7. Added for solubilization of poorly soluble metal complexes, surfactants decrease the rates of the
enzymatic reaction. The retardation effect increases in the series: cetyltrimethylammonium bromide < Triton X-100 < sodium
dodecyl sulfate, i.e. on going from positively charged to neutral and then to negatively charged surfactants. The behavior
of the OsIII and RuIII complexes toward reduced glucose oxidase contrasts to that of recently studied ferricenium cations. As opposed to the latter,
the former do not show kinetically meaningful binding with the enzyme, and the Michaelis kinetics typical of the ferricenium
case is not realized for the OsIII, and RuIII species. The systems OsIII- or RuIII-glucose oxidase are convenient for routine "one pot" spectrophotometric monitoring of the d-glucose content in samples, since the metal reduction to MII is accompanied by a strong increase in absorbance in the visible spectral region.
Received: 1 July 1998 / Accepted: 13 January 1999 相似文献
4.
Christopher D. Borman Colin G. Saysell A. G. Sykes 《Journal of biological inorganic chemistry》1997,2(4):480-487
Reactions (25 °C) of galactose oxidase, GOaseox from Fusarium NRRL 2903 with five different primary-alcohol-containing substrates RCH2OH:- D-galactose (I) and 2-deoxy-d-galactose (II) (monosaccharides); methyl-β-d-galactopyranoside (III) (glycoside);d-raffinose (IV) (trisaccharide); and dihydroxyacetone (V) have been studied in the presence of O2. The GOaseox state has a tyrosyl radical coordinated at a square-pyramidal CuII active site, and is a two-equivalent oxidant. Reactant concentrations were [GOaseox] (0.8–10 μM), RCH2OH (1.0–6.0 mM), and O2 (0.14–0.29 mM), with I=0.100 M (NaCl). The reactions, monitored at 450 nm by stopped-flow spectrophotometry, terminated with depletion of the O2. Each trace was fitted to the competing reactions GOaseox+RCH2 OH → GOaseredH2+RCHO (k
1), and GOaseredH2+O2→ GOaseox+H2O2 (k
2), with GOaseredH2 written as the doubly protonated two-electron-reduced CuI product. It was necessary to avoid auto-redox interconversion of GOaseox and GOasesemi . Information obtained at pH 7.5 indicates a 5 : 95 (ox : semi) "native" mix equilibration complete in ∼3 h. At pH >7.5,
rate constants 10–4 k
1 / M–1 s–1 for the reactions of GOaseox with (I) (1.19), (II) (1.07), (III) (1.29), (IV) (1.81), (V) (2.94) were determined. On decreasing the pH to 5.5, k
1 values decreased by factors of up to a half, and acid dissociation pK
as in the range 6.6–6.9 were obtained. UV-Vis spectrophotometric studies on GOaseox gave an independently determined pK
a of 6.7. No corresponding reactions of the Tyr495Phe variant were observed, and there are no similar UV-Vis absorbance changes
for this variant. The pK
a is therefore assigned to protonation of Tyr-495 which is a ligand to the Cu. The rate constant k
2 (1.01×107 M–1 s–1) is independent of pH in the range 5.5–9.0 investigated, suggesting that H+ (or H-atoms) for the O2 → H2O2 change are provided by the active site of GOasered . The CuI of GOasered is less extensively complexed, and a coordination number of three is likely.
Received: 4 February 1997 / Accepted: 16 May 1997 相似文献
5.
Joo-Yeon Han Astrid Gräslund Lars Thelander A. G. Sykes 《Journal of biological inorganic chemistry》1997,2(3):287-294
Four reductions of the R2 subunit of mouse ribonucleotide reductase have been studied and found to exhibit different behaviour
from that of Escherichia coli R2. An important difference is that there is no stable met-R2 (Fe2
II I) form of mouse R2. With hydroxyurea, hydrazine and hydroxylamine uniphasic kinetics are observed for the combined reduction
of radical Tyr ˙ and Fe2
II I components to tyrosine and Fe2
II respectively. The rate constants, determined at 370 nm (emphasising FeIII decay) and 417 nm (emphasising Tyr ˙ decay), differ by factors of 2–3, allowing some mechanistic features to be defined. The studies with hydrazine are particularly
important. In the case of E. coli R2, a first phase corresponding to two-equivalent reduction of the met-R2 component has been observed [18]. It is likely
that the four times slower second phase reaction of active E. coli R2 also corresponds to the Fe2
II I → Fe2
II change and is followed by fast intramolecular Fe2
II reduction of the higher potential Tyr ˙. The latter changes are believed to hold also for (active) mouse R2. The FeIIFeIII semi forms have been detected at low levels by EPR for mouse R2 (9%) and E. coli (∼5%) in previous studies. Further substrate reduction of FeIIFeIII occurs at a comparable rate to account for the transient behaviour of FeIIFeIII. For mouse R2 the combined FeIII decay processes (which we are unable to separate) give smaller uniphasic rate constants at 370 nm than at 417 nm. A fitted-base-line
(FBL) treatment of absorbance changes at 417 nm targets more closely the Tyr ˙ decay as a means of monitoring the rate-determining step. The FBL method gives rate constants k (M–1 s–1) at 25 °C and pH 7.5 for hydroxyurea (1.46), hydrazine (0.163) and hydroxylamine (4.4). Surprisingly, phenylhydrazine, with
a less strong reduction potential (0.25 V), gives a substantially faster reduction of the Tyr ˙ as the only redox step (rate constant 27 M–1 s–1). In this case a slower second phase at 370 nm is independent of reductant and corresponds to rate-controlling release of
FeIII. Overall the results indicate a more reactive redox centre for mouse R2 and help develop further an understanding of factors
affecting the reactivity of R2.
Received: 11 October 1996 / Accepted: 11 February 1997 相似文献
6.
Tiecheng Qiao Robert Witkowski Robin Henderson G. McLendon 《Journal of biological inorganic chemistry》1996,1(5):432-438
The kinetics of methemoglobin reduction by cytochrome b
5 has been studied by stopped-flow and saturation transfer NMR. A forward rate constant k
f = 2.44×104 M–1 s–1 and a reverse rate constant k
b = 540 M–1s–1 have been observed at 10 mm, pH 6.20, 25 °C. The ratio k
f/k
b = k
eq = 43.6 is in good agreement with the equilibrium constant calculated from the electrochemical potential between cyt b
5 and methemoglobin. A bimolecular collisional mechanism is proposed for the electron transfer from cyt b
5 to methemoglobin based on the kinetic data analysis. The dependence of the rate constants on ionic strengths supports such
collisional mechanism. It is also found that the reaction rate strongly depends on the conformations of methemoglobin.
Received: 20 February 1996 / Accepted: 4 June 1996 相似文献
7.
C. Immoos Michael G. Hill Donita Sanders James A. Fee Claire E. Slutter John H. Richards Harry B. Gray 《Journal of biological inorganic chemistry》1996,1(6):529-531
The electrochemistry of a water-soluble fragment from the CuA domain of Thermus thermophilus cytochrome ba
3
has been investigated. At 25 °C, CuA exhibits a reversible reduction at a pyridine-4-aldehydesemicarbazone-modified gold electrode (0.1 M Tris, pH 8) with E° = 0.24 V vs NHE. Thermodynamic parameters for the [Cu(Cys)2Cu]+/0 electrode reaction were determined by variable-temperature electrochemistry (ΔS°rc = –5.4(12) eu, ΔS° = –21.0(12) eu, ΔH° = –11.9(4) kcal/mol;ΔG° = –5.6 (11) kcal/mol). The relatively small reaction entropy is consistent with a low reorganization energy for [Cu(Cys)2Cu]+/0 electron transfer. An irreversible oxidation of [Cu(Cys)2Cu]+ at 1 V vs NHE confirms that the CuII:CuII state of CuA is significantly destabilized relative to the CuII state of analogous blue-copper proteins.
Received: 3 June 1996 / Accepted: 26 August 1996 相似文献
8.
Kinetics of the steady-state oxidation of n–alkylferrocenes (alkyl = H, Me, Et, Bu and C5H11) by H2O2 to form the corresponding ferricenium cations catalyzed by horseradish peroxidase has been studied in micellar systems of
Triton X-100, CTAB, and SDS, mostly at pH 6.0 and 25 °C. The rate of oxidation of ferrocenes with longer alkyl radicals is
too slow to be measured. The reaction obeying the [RFc]:[H2O2] = 2 : 1 stoichiometry is strictly first-order in both HRP and RFc in a wide concentration range. The corresponding observed
second-order rate constants k, which refer to the interaction of the peroxidase compound II (HRP-II) with RFc, decrease with the elongation of the alkyl
substituent R, and this in turn is accompanied by an increase in the formal redox potentials E°′ in the same medium. Increasing the surfactant concentration lowers the rate constants k, the effect being due to the nonproductive binding of RFc to micelles rather than to enzyme inactivation. The micellar effects
are accounted for in terms of the Berezin pseudo-phase model of micellar catalysis applied to the interaction of enzyme with
organometallic substrates. The oxidation was found to occur primarily in the aqueous pseudo-phase and the calculated intrinsic
second-order rate constants k
w are (1.9 ± 0.5)×105, (2.7 ± 0.1)×104, and (5.9 ± 0.6)×103 M–1 s–1 for HFc, EtFc, and n–BuFc, respectively. The data obtained were used for estimating the self-exchange rate constants for the HRP-II/HRP couple
in terms of the Marcus formalism.
Received: 15 July 1996 / Accepted: 15 November 1996 相似文献
9.
The intramolecular electron-transfer rate constant for the Cu(II)–topaNH2⇌ Cu(I)–topaSQ equilibrium in methylamine oxidase has been measured by temperature-jump relaxation techniques. At pH 7.0 the estimated kobs = 150±30 s–1 for both methylamine and benzylamine; assuming the equilibrium constant is ≈0.7–1 at pH 7.0 and 296 K, this would correspond
to a forward electron-transfer rate constant kET≈ 60–75 s–1. Although substantially slower than the previously determined kET≈ 20 000 s–1 for pea seedling amine oxidase [5] steady-state kinetics measurements established that kET > kcat≈ 4–10 s–1. Thus the Cu(I)-semiquinone state is a viable intermediate in methylamine oxidase turnover.
Received: 16 August 1995 / Accepted: 21 December 1995 相似文献
10.
Salmon sperm DNA platination has been conducted under strictly pseudo-first-order conditions with cisplatin (1) and rac-{(1S,2S,4S)-exo-2-(aminomethyl)-2-amino-7-bicyclo[2.2.1]heptane}dichloroplatinum(II) (2). An aquation step first occurs for both complexes, with the rate constants k
1 = 1.12(0.02)×10–4 s–1 and 1.47(0.02)×10–4 s–1 respectively for 1 and 2 at 37 °C, values in agreement with those previously reported. It is followed by the actual platination step whose second-order
rate constant has been determined for the first time by physicochemical techniques. The values for 1 and 2 respectively are: k
2 = 2.08(0.07) M–1 s–1 and 3.9(0.4) M–1 s–1. These kinetic data are discussed in the context of a comparison of several biological properties of the two complexes.
Received: 15 May 1998 / Accepted: 26 June 1998 相似文献
11.
《Inorganica chimica acta》1986,124(1):13-28
The reaction of [(H2O)(NH3)5RuII]2+ with calf thymus and salmon sperm DNA has been studied over a wide fange of transition metal ion concentrations. Kinetic studies revealcd a biphasic reaction with an initial fairly rapid coordination of the metal ion being followed by slower reactions. Binding studies were done under pseudo-equilibrium conditions following completion of the initial rapid reaction. Spectra and HPLC of acid-hydrolyzed samples of [(NH3)5RuII]n-DNA prepared by incubation of [(H2O)(NH3)5RuII]2+ with DNA (where [PDNA] = 1.5 mM and reactant [RuII]/[PDNA] ratios were in the fange 0.1 to 0.3) followed by air oxidation showed the predominant binding site on helical DNA to be in the major groove at the N-7 of guanine. The equilibrium constant for [(H2O)(NH3)5RuII]2+ binding to the G7 site in helical CT DNA is 5.1 x 103. Differential pulse voltammetry exhibited a single peak at 48 mV, which is attributed to the reduction of Rum on the G7 sites.At [Run]/[PDNA] <0.5, Tm values for the DNA decreased linearly with increasing ruthenium concentration and an increase in the intensity of the 565 nm dG→ Ru(III) charge transfer band was noted upon melting. The UV and CD spectra of these samples indicated no extensive destacking or alteration in geometry (B family) compared to unsubstituted DNA. At [Run]/[PDNA]〉 0.5 or when single-stranded DNA was used, increased absorbance at 530 nm and 480 nm suggested additional binding to the exocyclic amine sites of adenine and cytosine residues. HPLC and individual spectrophotometric identification of the products derived from hydrolysis of these spec~es yielded both [(Gua)(NH3)5RuIII] and [(Ade)(NH3)5RuIII]. Earlier studies have established the cytidine and adenosine binding sites of [(NH3)5RuIII] to be at their exocyclic amines (C4 and A6). Coordination to these positions indicates disruption of the double helix since these amines are involved in hydrogen bonding on the interior of B-DNA.Agrose gel electrophoresis of superhelical pBR322 plasmid DNA after exposure to various complexes of [(nh3)5Ruiii] in the presence of a reductant and air generally revealed moderately efficient cleavage of the DNA, presumably due to the generation of hydroxyl radical via Fenton's chemistry. However, similar studies involving [(NH3)5RuIII] directly coordinated to the DNA showed no strand cutting above background. Polyacrylamide gel electrophoresis of a 381 bp, 3′-32P-labeled fragment of pBR322 plasmid DNA containing low levels of bound [(NH3)5 RuIII] further indicated negligible DNA cutting by the coordinated metal ion. 相似文献
12.
Amalia Muñoz Frank Laib David H. Petering C. F. Shaw III 《Journal of biological inorganic chemistry》1999,4(4):495-507
The synthetic peptide fragment containing residues 49–61 of rabbit liver metallothionein II (MT-II) (Ac-Ile-Cys-Lys-Gly-Ala-Ser-Asp-Lys-Cys-Ser-Cys-Cys-Ala-COOH),
which includes the only sequential four cysteines bound to the same metal ion in Cd7MT, forms a stable, monomeric Cd-peptide complex with 1 : 1 stoichiometry (Cd:peptide) via Cd-thiolate interactions. This
represents the first synthesis of a single metal-binding site of MT independent of the domains. The 111Cd NMR chemical shift at 716 ppm indicates that the 111Cd2+ in the metal site is terminally coordinated to four side-chain thiolates of the cysteine residues. The pH of half dissociation
for this Cd-peptide derivative, ∼3.3, demonstrates an affinity similar to that for Cd7MT. Molecular mechanics calculations show that the thermodynamically most stable folding for this isolated Cd2+ center has the same counterclockwise chirality (Λ or S) observed in the native holo-protein. These properties are consistent with its proposed role as a nucleation center for cadmium-induced
protein folding. However, the kinetic reactivity of the CdS4 structure toward 5,5′-dithiobis(5-nitrobenzoate) (DTNB) and EDTA is greatly increased compared to the complete cluster (α-domain
or holo-protein). The rate law for the reaction with DTNB is rate=(k
uf +k
1,f +k
2,f [DTNB])[peptide], where k
uf=0.15 s–1, k
1,f=2.59×10–3 s–1, and k
2,f=0.88 M–1 s–1. The ultrafast step (uf), observable only by stopped-flow measurement, is unprecedented for mammalian (M7MT) and crustacean (M6MT) holo-proteins or the isolated domains. The accommodation of other metal ions by the peptide indicates a rich coordination
chemistry, including stoichiometries of M-peptide for Hg2+, Cd2+, and Zn2+, M2-peptide for Hg2+ and Au+, and (Et3PAu)2-peptide.
Received: 9 December 1998 / Accepted: 20 May 1999 相似文献
13.
Brendan J. Kennedy 《Inorganica chimica acta》1991,190(2)
A spectroelectrochemical study of [Ru2X9]n−, X=Cl, Br; n=1, 2, 3, 4 has been undertaken. Stable solutions of n=4, 2, 1 can be formed by electrolysis at low temperatures. Analysis of the Vis-NIR spectra of the complexes indicate that the RuII---RIII dimers (n=4) have delocalised mixed valence and that the RuIII---RIII (n=3) dimers have a strong Ru---Ru bond. The more oxidised materials do not form a Ru---Ru bond; the spectroscopic data indicates the RuIII---RIV dimers have localised valency. 相似文献
14.
É. Tóth Fabienne Connac Lothar Helm Kofi Adzamli André E. Merbach 《Journal of biological inorganic chemistry》1998,3(6):606-613
The Gd(III) complex of 4-pentylbicyclo[2.2.2]octane-1-carboxyl-di-l-aspartyl-lysine-derived DTPA, [GdL(H2O)]2–, binds to serum albumin in vivo, through hydrophobic interaction. A variable temperature 17O NMR, EPR, and Nuclear Magnetic Relaxation Dispersion (NMRD) study resulted in a water exchange rate of k
298
ex=4.2×106 s–1, and let us conclude that the GdL complex is identical to [Gd(DTPA)(H2O)]2– in respect to water exchange and electronic relaxation. The effect of albumin binding on the water exchange rate has been
directly evaluated by 17O NMR. Contrary to expectations, the water exchange rate on GdL does not decrease considerably when bound to bovine serum
albumin (BSA); the lowest limit can be given as k
ex, GdL-BSA=k
ex, GdL / 2. In the knowledge of the water exchange rate for the BSA-bound GdL complex, the analysis of its NMRD profile at 35 °C
yielded a rotational correlation time of 1.0 ns, one order of magnitude shorter than that of the whole protein. This value
is supported by the longitudinal 17O relaxation rates. This indicates a remarkable internal flexibility, probably due to the relatively large distance between
the protein- and metal-binding moieties of the ligand.
Received: 25 June 1998 / Accepted: 11 August 1998 相似文献
15.
Jose Neptuno Rodriguez-Lopez Andrew T. Smith R. N. F. Thorneley 《Journal of biological inorganic chemistry》1996,1(2):136-142
Horseradish peroxidase isoenzyme C (HRPC) mutants were constructed in order to understand the role of two key distal haem
cavity residues, histidine 42 and arginine 38, in the formation of compound I and in substrate binding. The role of these
residues as general acid-base catalysts, originally proposed for cytochrome c peroxidase by Poulos and Kraut in 1980 was assessed for HRPC. Replacement of histidine 42 by leucine [(H42L)HRPC*] decreased
the apparent bimolecular rate constant for the reaction with hydrogen peroxide by five orders of magnitude (k
1 = 1.4×102 M–1s–1) compared with both native-glycosylated and recombinant forms of HRPC (k
1 = 1.7×107 M–1s–1). The first-order rate constant for the heterolytic cleavage of the oxygen-oxygen bond to form compound I was estimated to
be four orders of magnitude slower for this variant. Replacement of arginine 38 by leucine [(R38L)HRPC*] decreased the observed
pseudo-first-order rate constant for the reaction with hydrogen peroxide by three orders of magnitude (k
1 = 1.1×104 M–1s–1), while the observed rate constant of oxygen bond scission was decreased sixfold (k
2 = 142 s–1). These rate constants are consistent with arginine 38 having two roles in catalysing compound I formation: firstly, promotion
of proton transfer to the imidazole group of histidine 42 to facilitate peroxide anion binding to the haem, and secondly,
stabilisation of the transition state for the heterolytic cleavage of the oxygen-oxygen bond. These roles for arginine 38
explain, in part, why dioxygen-binding globins, which do not have an arginine in the distal cavity, are poor peroxidases.
Binding studies of benzhydroxamic acid to (H42L)HRPC* and (R38L)HRPC* indicate that both histidine 42 and arginine 38 are
involved in the modulation of substrate affinity.
Received: 21 July 1995 / Accepted: 27 November 1995 相似文献
16.
S. C. J. Meskers C. Dennison Gerard W. Canters Harry P. J. M. Dekkers 《Journal of biological inorganic chemistry》1998,3(6):663-670
The dynamic quenching of the luminescence of racemic Eu(III)(pyridine-2,6-dicarboxylate=dpa)3
3– by the title proteins is investigated and the enantioselectivity of the proteins in the quenching of the Δ and Λ enantiomers
of Eu(dpa)3
3– is determined. The two diastereomeric quenching rate constants pertaining to azurin (k
q
Δ=3.3×106, k
q
Λ=2.7×106 M–1 s–1, pH 7.2, ionic strength I=22 mM) are lower than for its Met→44Lys mutant (k
q
Δ=1.9×107, k
q
Λ=1.4×107 M–1 s–1, same pH and I), indicating that energy transfer occurs from Eu(dpa)3
3– to the Cu(II) centre when the luminophore is bound to the hydrophobic patch of the protein near residue 44. The enantioselectivity
remains unaltered by the mutation: k
q
Δ/k
q
Λ=1.27±0.04, so Lys44 is probably not in direct contact with the Eu chelate. The I and pH dependence of k
q indicate that the lysine residue interacts electrostatically with Eu(dpa)3
3–. For plastocyanin the quenching rates are of the order of 106 M–1 s–1; for amicyanin they are two orders of magnitude larger (k
q
Δ=12×107, k
q
Λ=11×107 M–1 s–1, pH 7.2, I=22 mM). The variation of k
q is attributed to differences in the charge distribution on the proteins, which influences the binding of the luminophore
to the protein surface. For amicyanin the anion binding site near Lys59 and Lys60 may be involved in the energy transfer.
Received: 16 June 1998 / Accepted: 18 September 1998 相似文献
17.
Nigel J. Adams Berry Pinshow Leonard Z. Gannes 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(6):444-450
We used tritium-labeled water to measure total body water, water influx (which approximated oxidative water production) and
water efflux in free-flying tippler pigeons (Columba livia) during flights that lasted on average 4.2 h. At experimental air temperatures ranging from 18 to 27 °C, mean water efflux
by evaporation and excretion [6.3 ± 1.3 (SD) ml · h−1, n = 14] exceeded water influx from oxidative water and inspired air (1.4 ± 0.7 ml · h−1, n = 14), and the birds dehydrated at 4.9 ± 0.9 ml · h−1. This was not significantly different from gravimetrically measured mass loss of 6.2 ± 2.1 g · h−1 (t = 1.902, n = 14, P>0.05). This flight-induced dehydration resulted in an increase in plasma osmolality of 4.3 ± 3.0 mosmol · kg−1 · h−1 during flights of 3–4 h. At 27 °C, the increase in plasma osmolality above pre-flight levels (ΔP
osm = 7.6±4.29 mosmol · kg−1 · h−1, n = 6) was significantly higher than that at 18 °C (ΔP
osm = 0.83±2.23 mosmol · kg−1 · h−1, (t = 3.43, n = 6, P < 0.05). Post-flight haematocrit values were on average 1.1% lower than pre-flight levels, suggesting plasma expansion. Water
efflux values during free flight were within 9% of those in the one published field study (Gessaman et al. 1991), and within
the range of values for net water loss determined from mass balance during wind tunnel experiments (Biesel and Nachtigall
1987). Our net water loss rates were substantially higher than those estimated by a simulation model (Carmi et al. 1992) suggesting
some re-evaluation of the model assumptions is required.
Accepted: 8 April 1997 相似文献
18.
Ralph Beneke Katharina Meyer 《European journal of applied physiology and occupational physiology》1997,75(3):246-251
The effect of a 3-week exercise programme on performance and economy of walking was analysed in 16 male patients with chronic
heart failure [mean age 51.8 (SD 6.9) years, height 174.9 (SD 6.3) cm, body mass 75.3 (SD 11.5) kg, ejection fraction 20.8
(SD 5.0)%]. They were submitted to a cardiopulmonary exercise test on a cycle ergometer and a 6-min walking test on a treadmill
before and after the period of exercise training. The training programme consisted of interval cycle (five times a week for
15 min), and treadmill ergometer training (three times a week for 10 min) at approximately 70% cycling peak oxygen uptake
(O2peak) and supplementary exercises (three times a week for 20 min). Compared to the pre values cycling O2peak [11.9 (SD 2.9) vs 14.0 (SD 2.3) ml · kg–1 · min–1], maximal self paced walking speed [0.68 (SD 0.33) vs 1.16 (SD 0.30) m · s–1], and net walking power [2.16 (SD 0.89) vs 2.73 (SD 0.91) W · kg–1] had increased (P < 0.01) while net energy cost [3.31 (SD 0.66) vs 2.33 (SD 0.38) J · kg–1 · m–1] had decreased (P < 0.001) after the training period. Approximately 42% of the increase of walking speed resulted from a higher walking power
output, whereas approximately 58% corresponded to a positive effect on walking economy. The improvement in walking economy
was a function of an increase in walking velocity itself and a result of a more efficient walking technique. These results
would indicate that in patients with marked exercise intolerance, adequate exercise training programmes could contribute to
favourable metabolic changes with positive effects on the economy of motion.
Accepted: 29 August 1996 相似文献
19.
Pentaammineruthenium(III) complexes of deoxyinosine (dIno) and xanthosine (Xao) ([RuIII(NH3)5(L)], L?is?dIno, Xao) in basic solution were studied by UV?Cvis spectroscopy, liquid chromatography/electrospray ionization mass spectrometry, and high-performance liquid chromatography. Both RuIII complexes disproportionate to RuII and RuIV. Disproportionation followed the rate law d[RuII]/dt?=?(k o?+?k 1[OH?])[RuIII]. k o and k 1 of disproportionation at 25?°C were 2.1 (±0.1)?×?10?3?s?1 and 21.4?±?3.2?M?1 s?1, respectively, for [RuIII(NH3)5(dIno)], and 3.5 (±0.7)?×?10?4?s?1 and 59.7?±?3.6?M?1?s?1, respectively, for [RuIII(NH3)5(Xao)]. The [RuIII(NH3)5(Xao)] complex disproportionates at a faster rate than [RuIII(NH3)5(dIno)] owing to the stronger electron-withdrawing effect of exocyclic oxygen in Xao. The activation parameters ??H ? and ??S ? for k 1 of [RuIII(NH3)5(dIno)] were 80.2?±?15.2?kJ?mol?1 and 47.6?±?9.8?J?K?1 mol?1, respectively, indicating that the disproportionation of RuIII to RuII and RuIV is favored owing to the positive entropy of activation. The final products of both complexes in basic solution under Ar were compared with those under O2. Under both conditions [Ru(NH3)5(8-oxo-L)] was produced, but via different mechanisms. In both aerobic and anaerobic conditions, the deprotonation of highly positively polarized C8-H of Ru-L by OH? initiates a two-electron redox reaction. For the next step, we propose a one-step two-electron redox reaction between L and RuIV under anaerobic conditions, which differentiates from Clarke??s mechanism of two consecutive one-electron redox reactions between L, RuIII, and O2. 相似文献
20.
Aldegunde M Andrés MD Soengas JL 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(3):237-243
The influx of glucose into the brain and plasma glucose disappearance were estimated in rainbow trout (Oncorhynchus mykiss) intravenously injected (1 ml · kg−1 body weight) with a single dose (15 μCi · kg−1 body weight) of 3-O-methyl-D-[U-14C]glucose ([U-14C]-3-OMG) at different times (2–160 min), and after intravenous injection at 15 min of increased doses (10–60 μCi · kg−1 body weight) of [U-14C]-3-OMG. Brain and plasma radiotracer concentrations were measured, and several kinetic parameters were calculated. The apparent
brain glucose influx showed a maximum after 15–20 min of injection then decreased to a plateau after 80 min. Brain distribution
space of 3-OMG increased from 2 min to 20 min reaching equilibrium from that time onwards at a value of 0.14 ml · g−1. The unidirectional clearance of glucose from blood to brain (k1) and the fractional clearance of glucose from brain to blood (k2) were estimated to be 0.093 ml · min−1 · g−1, and 0.867 min−1, respectively. A linear increase was observed in brain and plasma radiotracer concentrations when increased doses of [U-14C]-3-OMG were used. All these findings support a facilitative transport of glucose through the blood-brain barrier of rainbow
trout with characteristics similar to those observed in mammals. The injection of different doses of melatonin (0.25–1.0 mg · kg−1) significantly increased brain glucose influx suggesting a possible role for melatonin in the regulation of glucose transport
into the brain.
Accepted: 26 January 2000 相似文献