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1.
Summary The effect of trace elements (Fe, Ni) and chelating compounds on the activity of hydrogen (H 2) uptake (Hup) hydrogenase, nitrogenase and rate and yield of H 2 photoproduction from l-lactate in photosynthetic cultures of Rhodospirillum rubrum was investigated. Hup activity depended on the availability of Ni 2+ and was inhibited by EDTA (0.3–0.5 m m ethylenedinitrilotetraacetic acid). Addition of EDTA (0.5 m m) to the culture medium caused a nearly complete inactivation of Hup activity and activation of nitrogenase, which was paralleled by a threefold increase in total H 2 photoproduced from lactate. Hup – mutants, isolated by transposon Tn 5 mutagenesis, produced maximally twofold more H 2 than the wild-type. Experiments with different chelating agents [EDTA, NTA (nitrilotriacetic acid), citrate, isocitrate] and varying concentrations of Fe 2+ and Fe 3+ showed that photosynthetic growth and nitrogenase activity of R. rubrum were strongly influenced by the iron supply. It is concluded that EDTA enhanced H 2 photoproduction by (I) inhibition of biosynthesis of Hup hydrogenase and (II) mobilization of iron, thereby activating the biosynthesis of the nitrogenase complex.
Correspondence to: M. Kern 相似文献
2.
N-Acyl- D-glutamate amidohydrolase ( D-AGase) was inhibited by 94 % when 1 mol/l N-acetyl- DL- glutamate was used as a substrate. The addition of 1 m M Co 2+ stabilized D-AGase. Moreover, the substrate inhibition was weakened to 88% with the addition of 0.4 m M Co 2+ to the reaction mixture. Although D-AGase is a zinc-metalloenzyme, the addition of Zn 2+ from 0.01 to 10 m M did not increase the D-glutamic acid production in the saturated substrate. Under optimal conditions, 0.38 M D-glutamic acid was obtained from N-acyl- DL-glutamate with 100% of the theoretical yield after 48 h. 相似文献
3.
The common metal chelation agents, DTPA and EDTA are often used as models for physiological low-molecular weight iron complexes in biochemical studies, or for common biochemical protocols. In the biochemical literature there are apparent conflicts as to whether EDTA and DTPA are pro-oxidant or antioxidant additives. This apparent conflict is puzzling since in chemical systems Fe IIEDTA and Fe IIDTPA are well known Fenton reaction reagents. In this investigation we examined the voltammetric characteristics of the iron complexes of EDTA, DTPA, and citrate and the effect of the ligand:metal ratio (L:M) on the electrocatalytic (EC') waves that result from reduction of H 2O 2 by this complex. At a ratio of 1:1, the cyclic voltammetric waves of the complexes indicate the presence of a reversible species corresponding to the Fe II/IIIL couple, along with a second irreversible reduction peak. The second irreversible voltammetric peak decreases at higher L:M ratios for EDTA and citrate. The 1:1 iron complexes of EDTA, DTPA, and citrate clearly induce the catalytic reduction of H 2O 2. In the presence of a greater than 100 fold excess of H 2O 2 relative to iron, higher L:M ratios greatly reduced the catalytic EC' wave compared to the 1:1 ratios. At H 2O 2:Fe ratios less than 50, the L:M ratio has very little effect of the EC' current. These observations may explain the apparent discrepancies in the biochemical literature. Addition of EDTA or DTPA may enhance oxidative processes if the L:M is low (less than unity), whereas rates of on-going oxidative processes may decrease if that ratio, along with the relative amount of H 2O 2, are both high (excess ligand). The impact of this study is of particular importance given the widespread use of these ligands in biochemical studies. 相似文献
4.
A new hypothesis describing the role of the redox inactive Ca 2+ ion in the expression of physiological oxidative damage is described. The hypothesis is based on the optimization of the chelation characteristics of iron complexes for pro-oxidant activity. In a previous investigation it was found that an excess of ligand kinetically hindered the Fenton reaction activity of the Fe II/IIIEDTA complex (Bobier et al. 2003). EDTA, citrate, NTA, and glutamate were selected as models for the coordination sites likely encountered by mobile iron, i.e. proteins. The optimal [EDTA]:[Fe III] ratio for Fenton reaction activity as measured by electrocatalytic voltammetry in a solution was found to be 1:1. An excess of EDTA in the amount of 10:1 [ligand]:[metal] suppresses the Fenton reaction activity to nearly the control. It is expected that the physiological coordination characteristics of mobile Fe would have a very large excess of [ligand]:[metal] and thus not be optimized for the Fenton reaction. Introduction of Ca 2+ in to a ratio of 10:10:1 [Ca 2+]:[EDTA]:[Fe III] to the system reinvigorated the Fenton reaction activity to nearly the value of the optimal 1:1 [EDTA]:[Fe III] complex. The pH distribution diagrams of Ca 2+ in the presence of EDTA and Fe II/III indicate that Ca 2+ has the ability to uptake excess EDTA without displacing either Fe II of Fe III from their respective complexed forms. The similarity in the presence for hard ligand sites albeit with a lower binding constant for Ca 2+ accounts for this action. 相似文献
5.
Supernatant of a culture of Bacillus pumilus D 78 was precipitated with ethanol and chromatographed on DEAE- and CM-cellulose to isolate and purify a neutral protease
with fibrinolytic and caseinolytic activity. Analysis by ultracentrifugation and immunoelectrophoresis indicate the homogeneity
of the purified enzyme with the sedimentation constant s 20,w equal to 2.3. The fibrinolytic activity had a lower heat stability and was also more sensitive to pH higher than 8.0. The
caseinolytic activity was stable over a wide range of pH (4.5 to 11.0). The enzyme binds acid dyes and is inhibited by Cu 2+, Zn 2+, Ca 2+ and Fe 3+, as well as by L-cysteine and KCN at a concentration of 10 mM. Likewise, EDTA and p-chloromercuribenzoate show an inhibitory effect. 相似文献
6.
以羊草幼苗为研究对象,通过调整全营养培养基(CK,0.05 mmol/L Fe 2+、0.015 mmol/L Zn 2+)中铁或者锌含量设置0、10倍、20倍Fe 2+(Zn 2+)浓度处理Fe 0(Zn 0)、Fe 10(Zn 10)、Fe 20(Zn 20),以及在高铁培养基中单独添加0.15 mmol/L Zn 2+或同时添加10 mmol/L Ca 2+、5 mmol/L Mg 2+、20 mmol/L K +处理,测定培养6 d后幼苗生长指标和矿质元素含量、以及高铁(Fe 20)处理下幼苗根中抗氧化指标和相关基因表达量,探究不同浓度Fe 2+、Zn 2+对羊草幼苗生长、矿质元素吸收积累及抗氧化指标、基因表达的影响。结果表明:(1)缺锌(Zn 0)显著抑制羊草幼苗鲜重的增加和Zn元素的积累,但促进Fe、Mg元素的积累;高浓度锌(Zn 10、Zn 20)显著促进幼苗叶片生长和Zn元素的积累;缺铁(Fe 0)显著抑制幼苗的根长、鲜重和Fe元素的积累,促进Mg、Zn元素的积累;高浓度铁(Fe 10、Fe 20)显著抑制羊草幼苗根叶生长、根毛发育和Ca、Zn、Mg、K元素的积累。(2)增加Zn 2+和Ca 2+、Mg 2+、K +浓度无法恢复高铁胁迫对幼苗生长的抑制作用。(3)高浓度铁(Fe 20)处理羊草幼苗48 h后,根部过氧化物酶、超氧化物歧化酶、过氧化氢酶、抗坏血酸过氧化物酶、谷胱甘肽还原酶活性和丙二醛、抗坏血酸、还原型谷胱甘肽含量显著升高;烟酰胺合成酶基因、过氧化物酶基因表达量显著下调,植物类萌发素蛋白基因表达量显著上调。研究发现,羊草幼苗生长发育和矿质元素积累对环境中Zn 2+浓度变化不敏感,却受到环境中高浓度Fe 2+的显著抑制,并造成严重的氧化胁迫伤害,这种伤害无法在添加Zn 2+或同时添加Ca 2+、Mg 2+、K +的条件下恢复。 相似文献
7.
In an attempt to elucidate the effect of metallic ions and EDTA on acidic α- d-glucosidase activity, we measured acidic α- d-glucosidase activity from either lymphocyte and muscle tissue homogenates or intact cells after incubation with metallic
ions. The results showed that this enzyme activity was strongly inhibited by Ag +, Hg 2+, and Fe 3+ in either lymphocyte or muscle tissue homogenates. There was no effect of Zn 2+, Cu 2+, and Cd 2+. However, intact cells, either lymphocyte or muscle cells, after incubation with Zn 2+ for 1 or 2 hr, showed enhanced enzyme activity and suppression in the other metallic ion groups, especially in Ag +, Hg 2+, and Fe 3+. Since deficiency of this enzyme can cause type II glycogen storage disese (Pompe’s disease), the more we understand the
character of this enzyme, the more we can improve our enzymatic therapy.
This work was supported by Grant NSC75-0412-B075-41 from the National Science Council of the Republic of China. 相似文献
8.
Nicotianamine (NA) occurs in all plants and chelates metal cations, including Fe II, but reportedly not Fe III. However, a comparison of the Fe II and Zn II affinity constants of NA and various Fe III-chelating aminocarboxylates suggested that NA should chelate Fe III. High-voltage electrophoresis of the FeNA complex formed in the presence of Fe III showed that the complex had a net charge of 0, consistent with the hexadentate chelation of Fe III. Measurement of the affinity constant for Fe III yielded a value of 10 20.6, which is greater than that for the association of NA with Fe II (10 12.8). However, capillary electrophoresis showed that in the presence of Fe II and Fe III, NA preferentially chelates Fe II, indicating that the Fe IINA complex is kinetically stable under aerobic conditions. Furthermore, Fe complexes of NA are relatively poor Fenton reagents, as measured by their ability to mediate H 2O 2-dependent oxidation of deoxyribose. This suggests that NA will have an important role in scavenging Fe and protecting the cell from oxidative damage. The pH dependence of metal ion chelation by NA and a typical phytosiderophore, 2′-deoxymugineic acid, indicated that although both have the ability to chelate Fe, when both are present, 2′-deoxymugineic acid dominates the chelation process at acidic pH values, whereas NA dominates at alkaline pH values. The consequences for the role of NA in the long-distance transport of metals in the xylem and phloem are discussed. 相似文献
9.
The hypothesized role of secreted reducing compounds in Fe III reduction has been examined with Fe-deficient peanuts ( Arachis hypogaea L. cv A124B). Experiments involved the exposure of roots to (a) different gas mixtures, (b) carbonyl cyanide m-chlorophenylhydrazone (CCCP), and (c) agents which impair membrane integrity. Removing roots from solution and exposing them to air or N2 for 10 minutes did not result in any accumulation in the free space of compounds capable of increasing rates of FeIII reduction when roots were returned to solutions. On the contrary, exposing roots to N2 decreased rates of FeIII reduction. CCCP also decreased rates of FeIII reduction. Acetic acid and ethylenediaminetetraacetic acid (disodium salt) (EDTA) impaired the integrity and function of the plasma membranes of roots of Fe-deficient peanuts. That is, in the presence of acetic acid or EDTA, there was an efflux of K+ from the roots; K+ (86Rb) uptake was also impaired. Acetic acid increased the efflux from the roots of compounds capable of reducing FeIII. However, both acetic acid and EDTA caused rapid decreases in rates of FeIII reduction by the roots. In addition to peanuts, acetic acid also decreased rates of FeIII reduction by roots of Fe-deficient sunflowers (Helianthus annuus L. cv Sobrid) but not maize (Zea mays L. cv Garbo). These results suggest that, at least in the short term, the enhanced FeIII reduction by roots of Fe-deficient plants is not due to the secretion of reducing compounds. 相似文献
10.
A new five coordinate and stable iron(III) heme analog, [Fe III(OEP)(DicydH)], where OEP is the dianion of octaethylporphyrin and DicydH = monoanion of 1,4-phenyldicyanamide, has been synthesized. The compound has been characterized by different spectroscopic methods 1H NMR, UV-Vis, IR as well as elemental analysis. 1H NMR spectroscopy and magnetic moment measurements show that [Fe III(OEP)(DicydH)] is paramagnetic and iron is five-coordinate. The structure of [Fe III(OEP)(DicydH)] has been determined by X-ray diffraction analysis, that it is similar with a P2 1/ c space group in the monoclinic crystal system. The crystal structure of the complex is stabilized by hydrogen bonds of the type N-H?N. Electrochemical of [Fe III(OEP)(DicydH)] has been studied by cyclic voltammetry. 相似文献
11.
The reactions of hydroxylamine (HA) with several water-soluble iron(III) porphyrinate compounds, namely iron(III) meso-tetrakis-( N-ethylpyridinium-2yl)-porphyrinate ([Fe III(TEPyP)] 5+), iron(III) meso-tetrakis-(4-sulphonatophenyl)-porphyrinate ([Fe III(TPPS)] 3−), and microperoxidase 11 ([Fe III(MP11)]) were studied for different [Fe III(Porph)]/[HA] ratios, under anaerobic conditions at neutral pH. Efficient catalytic processes leading to the disproportionation of HA by these iron(III) porphyrinates were evidenced for the first time. As a common feature, only N 2 and N 2O were found as gaseous, nitrogen-containing oxidation products, while NH 3 was the unique reduced species detected. Different N 2/N 2O ratios obtained with these three porphyrinates strongly suggest distinctive mechanistic scenarios: while [Fe III(TEPyP)] 5+ and [Fe III(MP11)] formed unknown steady-state porphyrinic intermediates in the presence of HA, [Fe III(TPPS)] 3− led to the well characterized soluble intermediate, [Fe II(TPPS)NO] 4−. Free-radical formation was only evidenced for [Fe III(TEPyP)] 5+, as a consequence of a metal centered reduction. We discuss the catalytic pathways of HA disproportionation on the basis of the distribution of gaseous products, free radicals formation, the nature of porphyrinic intermediates, the Fe II/Fe III redox potential, the coordinating capabilities of each complex, and the kinetic analysis. The absence of revealed either that no HAO-like activity was operative under our reaction conditions, or that , if formed, was consumed in the reaction milieu. 相似文献
12.
EstA was purified from the supernatant by A. lwoffii 16C-1. Its molecular mass was determined to be 45 kDa, and the optimal activity occurred when the pH level was 8.0 at a temperature
of 37°C. The activation energies for the hydrolysis of p-nitrophenyl butyrate was determined to be 11.25 kcal/mol in the temperature range of 10–37°C. The enzyme was unstable at
temperatures higher than 50°C. The Michaelis constant ( K
m
) and V
max for p-nitrophenyl butyrate were 11 μ M and 131.6 μ M min −1 mg of protein-1, respectively. The enzyme was strongly inhibited by Hg 2−, Ca 2+, Mg 2+, Fe 2+, Cu 2+, Zn 2+, Mn 2+, Co 2+, ethylemediaminetetraacetic acid (EDTA), phenylmethylsulfonyl fluoride (PMSF), and diisopropyl fluorophosphate (DFP).
Received: 20 August 2001 / Accepted: 20 September 2001 相似文献
13.
The kinetics of the formation of the purple complex [Fe III(EDTA)O 2] 3−, between Fe III-EDTA and hydrogen peroxide was studied as a function of pH (8.22-11.44) and temperature (10-40 °C) in aqueous solutions using a stopped-flow method. The reaction was first-order with respect to both reactants. The observed second-order rate constants decrease with an increase in pH and appear to be related to deprotonation of Fe III-EDTA ([Fe(EDTA)H 2O] − ⇔ Fe(EDTA)OH] 2− + H +). The rate law for the formation of the complex was found to be d[Fe IIIEDTAO 2] 3−/d t=[( k4[H +]/([H +] + K1)][Fe III-EDTA][H 2O 2], where k4=8.15±0.05×10 4 M −1 s −1 and p K1=7.3. The steps involved in the formation of [Fe(EDTA)O 2] 3− are briefly discussed. 相似文献
14.
In this work we present the synthesis and characterization of the complex dichloro[ N-propanoate- N, N-bis-(2-pyridylmethyl)amine]iron(III) [Fe III(PBMPA)Cl 2]. The ligand LiPBMPA was synthesized through the Michael reaction of BMPA with methylacrylate, followed by alkaline hydrolysis. The complex [Fe III(PBMPA)Cl 2] has been synthesized by the reaction of the ligand with FeCl 3 · H 2O and was mainly characterized by cyclic voltammetry, conductivimetry, and electronic, infrared and Mössbauer spectroscopies, and by X-ray structural analysis, which showed an iron center coordinated by one carboxylate oxygen in a monodentate way, one tertiary amine, two pyridine groups and two chloride ions. It has been proposed that in water the chloride ligands are shifted by the solvent molecules and the species [Fe III(PBMPA)(H 2O) 2]Cl 2 is predominant. The catalase-like activity of the complex was tested in water, and it proved to be active in the hydrogen peroxide dismutation. Kinetics studies were conducted following the initial rates method. The reaction is first order in relation to both the complex and the hydrogen peroxide. Based on the presence of a lag phase that depends on the initial complex concentration, we propose that the active species that shows in situ catalase-like activity, is a binuclear complex. 相似文献
15.
Crystal structures of polypeptide deformylase (PDF) of Escherichia coli with nickel(II) replacing the native iron(II) have been solved with chloride and formate as metal ligands. The chloro complex
is a model for the correct protonation state of the hydrolytic hydroxo ligand and the protonated status of the Glu133 side
chain as part of the hydrolytic mechanism. The ambiguity that recently some PDFs have been identified with Zn 2+ ion as the active-site centre whereas others are only active with Fe 2+ (or Co 2+, Ni 2+) is discussed with respect to Lewis acid criteria of the metal ion and substrate activation by the CD loop. 相似文献
16.
Nucleotide pyrophosphatase from yeast was inhibited by thiols, o-phenanthroline, 8-hydroxyquinoline, EDTA, and 8-hydroxyquinoline-5-sulfonic acid. The inhibition by chelating agents was time and concentration dependent. Inhibition by EDTA was decreased by complexing the EDTA with metal ions before addition to the enzyme. The effectiveness of the metal ions in preventing inhibition by EDTA paralleled the stability constants of the EDTA-metal complexes. Partial recovery of EDTA-inhibited enzyme activity was achieved with Zn 2+, Co 2+, Fe 2+, and Mn 2+. Analyses for zinc in the purified enzyme by atomic absorption spectroscopy and by titration with 8-hydroxyquinoline-5-sulfonic acid revealed the presence of approximately 1 g atom/mol of enzyme ( Mr 65,000). The data indicate that yeast nucleotide pyrophosphatase is a metalloenzyme in which the zinc plays some role in activity. 相似文献
17.
DFT (B3LYP and M06L) as well as ab initio (MP2) methods with Dunning cc-pVnZ ( n?=?2,3) basis sets are employed for the study of the binding ability of the new class of protease inhibitors, i.e., silanediols, in comparison to the well-known and well-studied class of inhibitors with hydroxamic functionality (HAM). Active sites of metalloproteases are modeled by [R 3M-OH 2] 2+ complexes, where R stands for ammonia or imidazole molecules and M is a divalent cation, namely zinc, iron or nickel (in their different spin states). The inhibiting activity is estimated by calculating Gibbs free energies of the water displacement by metal binding groups (MBGs) according to: [R 3M-OH 2] 2+ + MBG → [R 3M-MBG] 2+ + H 2O. The binding energy of silanediol is only a few kcal mol ?1 inferior to that of HAM for zinc and iron complexes and is even slightly higher for the triplet state of the (NH 3) 3Ni 2+ complex. For both MBGs studied in the ammonia model the binding ability is nearly the same, i.e., Fe 2+(t) > Ni 2+(t) > Fe 2+(q) > Ni 2+(s) > Zn 2+. However, for the imidazole model the order is slightly different, i.e., Ni 2+(t) > Fe 2+(t) > Fe 2+(q) > Ni 2+(s) ≥ Zn 2+. Equilibrium structures of the R 3Zn 2+ complexes with both HAM and silanediol are characterized by the monodentate binding, but the bidentate character of binding increases on going to iron and nickel complexes. Two types of intermediates of the water displacement reactions for [(NH 3) 3M-OH 2] 2+ complexes were found which differ by the direction of the attack of the MBG. Hexacoordinated complexes exhibit bidentate bonding of MBGs and are lower in energy for M=Ni and Fe. For Zn penta- and hexacoordinated complexes have nearly the same energy. Intermediate complexes with imidazole ligands have only octahedral structures with bidentate bonding of both HAM and dimethylsilanediol molecules. 相似文献
18.
Experiments were performed which illustrate the various ways EDTA can influence lipid peroxidation. Either detergent-dispersed linoleate, or liposomes made from extracted microsomal phospholipids were utilized as substrates for peroxidation. Peroxidation was accomplished using Fe 2+ or Fe 3+. In systems utilizing Fe 2+, EDTA chelation facilitated Fe 2+ autoxidation which in turn caused peroxidation of detergent-dispersed linoleate. Peroxidation was not initiated during EDTA-Fe 2+ autoxidation when the substrate lipids were in a liposomal configuration. Systems utilizing Fe 3+ required an enzyme (either xanthine oxidase or NADPH-cytochrome P450 reductase) to reduce the iron for peroxidative activity. EDTA chelation of Fe 3+ enhanced the xanthine oxidase and NADPH-cytochrome P450 reductase-catalyzed peroxidation of detergent-dispersed linoleate, presumably by facilitating the reduction of Fe 3+. Catalase and mannitol inhibited both EDTA-Fe 2+- and EDTA-Fe 3+-dependent lipid peroxidation. EDTA-Fe 3+ was not capable of initiating peroxidation of phospholipid liposomes following enzymatic reduction by either enzyme, but ADP-chelated iron effectively initiated liposomal peroxidation in similar systems. With xanthine oxidase-catalyzed peroxidation of liposomes with ADP-Fe 3+, the inclusion of EDTA-Fe 3+ caused a modest enhancement of activity. EDTA-Fe 3+ greatly stimulated NADPH-cytochrome P450 reductase-catalyzed peroxidation of liposomes with ADP-Fe 3+. In contrast, the addition of EDTA, rather than EDTA-Fe 3+ inhibited the liposomal peroxidation catalyzed by either enzyme with ADP-Fe 3+ when the EDTA concentration exceeded the concentration of Fe 3+. 相似文献
19.
Amyloid beta (Aβ) aggregation and oxidative stress are two of the central events in Alzheimer's Disease (AD). Both these phenomena can be caused by the interaction of Aβ with metal ions. In the last years the interaction between Zn II, Cu II, and Aβ was much studied, but between iron and Aβ it is still little known. In this work we determine how three Aβ peptides, present in AD, interact with Fe III‐citrate. The three Aβ peptides are: full length Aβ1‐42, an isoform truncated at Glutamic acid in position three, Aβ3‐42, and its pyroglutamated form AβpE3‐42. Conformation and morphology of the three peptides, aggregated with and without Fe III‐citrate were studied. Besides, we have determined the strength of the interactions Aβ/Fe III‐citrate studying the effect of ethylenediaminetetraacetic acid as chelator. Results reported here demonstrate that Fe III‐citrate promotes the aggregation in all the three peptides. Moreover, Aspartic acid 1, Glutamic acid 3, and Tyrosine 10 have an important role in the coordination with iron, generating a more stable complex for Aβ1‐42 compared to that for the truncated peptides. 相似文献
20.
Summary This paper describes the engineering of braced tripod proteins for use as molecular frameworks. Specifically, a 30-residue
tripod-shaped protein with three proline-II helical legs braced by an iron(II)tris(bipyridine) complex was modularly designed,
chemically synthesized, and biophysically characterized. Three copies of a 10-residue leg peptide were covalently linked through
sulfide bonds to an N-terminal apex (1,3,5-tris(methylene)benzene) and by amide bonds to the brace (Fe II (Mbc) 3: Mbc is 4′-methyl-2,2′-bipyridine-4-carbonyl). The leg peptide (H-Cys-Pro 5-Pra(Mbc)-Pro 3-NH 2: Pra is cis-4-amino- l-proline) was assembled by the solid-phase method using Boc-Pra(Mbc)-OH, which was synthesized in 75% overall yield by coupling
Mbc-OH to the 4-amino group of Boc-Pra-OCH 3 and saponifying the methyl ester group. The iron(II)-braced tripod was assembled by S-alkylation of three copies of the leg
peptide with 1,3,5-tris(bromomethyl)benzene followed by ligation of Fe 2+ to the resulting unbraced tripod. The CD spectrum of the iron(II)-braced tripod showed a positive MLCT band at 570 nm and
a negative π-π * band at 312 nm, so its Fe II(Mbc) 3 brace was predominantly in the Δ configuration. In a mostly acetonitrile solution at 25°C, the leg peptide and the unbraced
tripod isomerized from the proline-II helical form into the proline-I helical form but the iron(II)-braced tripod remained
in the proline-II helical form. 相似文献
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