共查询到20条相似文献,搜索用时 31 毫秒
1.
The protonation constants of 1,3,5-trideoxy-1,3,5-tris(2-hydroxyl-benzyl)amino-cis-inositol (thci) in I = 1 M (NaClO4) were determined to be: pKa1 5.96 ± 0.03, pKa2 7.21 ± 0.01, pKa3 8.32 ± 0.07, pKa4 8.95 ± 0.06. The solvent extraction studies were consistent with the formation of the Ln(thci)3+ and complexes. The log of the stability constants (log β1 and log β2) at 25 °C in 1 M (NaClO4) at pH 4 for formation of these complexes are reported. Laser luminescence measurements of the 7F0-5D0 transition of Eu(III) complexed by thci indicated two species. The shifts in the peaks relative to that of Eu(aq)3+ were comparable to the values reported for other complexes of Eu(III) with organic ligands, but the intensities were greater. Luminescence lifetime measurements of the fluorescence spectra indicated that the complex has 5 inner sphere water molecules bound to the Eu(III) cation at pH 6.71-8.52. This was consistent with bidentate chelation of Eu(III) with each thci molecule. gaussian view energy calculations indicated bonding for M(III) to the amino and hydroxyl groups of the cyclohexanetriol and (2-hydroxybenzyl)amino moieties in the Ln(thci)3+ complex. 相似文献
2.
Jacques Baudier Kenneth Haglid Jacques Haiech Dominique Gérard 《Biochemical and biophysical research communications》1983,114(3):1138-1146
Comparative studies have been performed on the binding properties of zinc ions to human brain calmodulin and S100b protein. Calmodulin is characterized by two sets of Zn2+ binding sites, with KD ranging from 8.10?5M to 3.10?4M. The S100b protein also exhibited two sets of zinc binding sites, with a much higher affinity. KD = 10?7 ? 10?6M. We suggest that S100b protein should no longer be considered only as a “calcium binding protein” but also as a “zinc binding protein”, and that Zn2+ ions are involved in the functions of the S100 proteins. 相似文献
3.
Summary Humic and fulvic-zinc complexes obtained from soil and poultry litter were characterized by I.R. spectroscopy, determination of stability constant and the free energy change associated with their formation. Infrared spectroscopy confirmed that both electrovalent, coordinate-covalent bonds of Zn2+ with the carboxylate, phenolic hydroxyl and amine groups lead to the formation of their stable complexes. This is evident from the changes in absorption bands at 1700 cm–1, 1725 cm–1, 1625 cm–1 and 1400 cm–1 of their infrared spectra.The stability constants of complexes are pH-dependent. Interaction of Zn with humic and fulvic acid involved the formation of mononuclear complexes. The values of stability constants of these complexes are lower than those reported earlier.The calculation of the free-energy change associated with salts and complex formation indicates the spontaneity of both reactions, although a higher probability of complex reaction than that of salt formation is evident. The implications of the complexation of metal ions by these naturally occurring polydisperse plyaanions in regulating the movement of metal ions from the ambient soil matrix to plant roots and biological system in terresterial and aquatic environments are indicated.Journal paper no. 2, Department of Soil Science and Agricultural Chemistry, Rajendra Agricultural University, Tirhut College of Agriculture, Dholi, Muzaffarpur, Bihar, India. 相似文献
4.
Glutamate synthase (E.C. 1.4.1.14) (GOGAT) activity was not detectable in L3 Haemonchus contortus, but was present in L3 Teladorsagia circumcincta and adult worms of both species. GOGAT activity was inhibited by 80% by azaserine. Activity (nmol min−1 mg−1 protein) was 33–59 in adult H. contortus, 51–91 in adult T. circumcincta and 24–41 in L3 T. circumcincta, probably depending on exposure to ammonia, as incubation with 1 mM NH4Cl doubled GOGAT activity. The pH optimum was 7.5 in both species. Either NAD or NADP acted as co-factor. The mean apparent Km for 2-oxoglutarate was 0.7 (0.5–0.9) mM and for glutamine was 1.0 (0.5–1.7) mM for different homogenates. There was no detectable activity in whole parasite homogenates of glutamate decarboxylase (E.C. 4.1.1.15) or succinic semialdehyde dehydrogenase (E.C. 1.2.1.24), the first and third enzymes of the GABA shunt, respectively, suggesting that the GABA shunt is not important in general metabolism in these species. 相似文献
5.
Anatoly F. Vanin Xiaoping Liu Alexandre Samouilov Reonald A. Stukan Jay L. Zweier 《Biochimica et Biophysica Acta (BBA)/General Subjects》2000,1474(3):365-377
While the Fe2+–dithiocarbamate complexes have been commonly used as NO traps to estimate NO production in biological systems, these complexes can undergo complex redox chemistry. Characterization of this redox chemistry is of critical importance for the use of this method as a quantitative assay of NO generation. We observe that the commonly used Fe2+ complexes of N-methyl-D-glucamine dithiocarbamate (MGD) or diethyldithiocarbamate (DETC) are rapidly oxidized under aerobic conditions to form Fe3+ complexes. Following exposure to NO, diamagnetic NO–Fe3+ complexes are formed as demonstrated by the optical, electron paramagnetic resonance and gamma-resonance spectroscopy, chemiluminescence and electrochemical methods. Under anaerobic conditions the aqueous NO–Fe3+–MGD and lipid soluble NO–Fe2+–DETC complexes gradually self transform by reductive nitrosylation into paramagnetic NO–Fe2+–MGD complexes with yield of up to 50% and the balance is converted to Fe3+–MGD and nitrite. In dimethylsulfoxide this process is greatly accelerated. More efficient transformation of NO–Fe3+–MGD into NO–Fe2+–MGD (60–90% levels) was observed after addition of reducing equivalents such as ascorbate, hydroquinone or cysteine or with addition of excess Fe2+–MGD. With isotope labeling of the NO–Fe3+–MGD with 57Fe, it was shown that these complexes donate NO to Fe2+–MGD. NO–Fe3+–MGD complexes were also formed by reversible oxidation of NO–Fe2+–MGD in air. The stability of NO–Fe3+–MGD and NO–Fe2+–MGD complexes increased with increasing the ratio of MGD to Fe. Thus, the iron–dithiocarbamate complexes and their NO derivatives exhibit complex redox chemistry that should be considered in their application for detection of NO in biological systems. 相似文献
6.
Monica A. Lewis Seymour Mong Robert L. Vessella G. Kurt Hogaboom Hsiao-Ling Wu Stanley T. Crooke 《Prostaglandins & other lipid mediators》1984,27(6):961-974
Specific leukotriene C4 (LTC4) binding sites were identified in membrane preparations from human fetal lung. Specific binding of [3H]-LTC4 represented 95 percent of total binding, reached steadystate within 10 minutes and was rapidly reversible upon addition of excess unlabeled LTC4. Binding assays were performed at 4°C under conditions which prevented metabolism of [3H]-LTC4 (80 mM serineborate, 10 mM cysteine, 10 mM glycine). Under these conditions, greater than 95 percent of the membrane bound radioactivity, as analyzed by high performance liquid chromatography, co-eluted with the LTC4 standard. Computer-assisted analyses of saturation binding data showed a single class of binding sites with a dissociation constant (Kd) of 26 + 6 nM and a density (Bmax) of 84 ± 18 pmol/mg protein. Pharmacological specificity was demonstrated by competition studies in which specific binding of [3H]-LTC4 was displaced by LTC4 and its structural analogs with inhibition constants (Kj) of 10 to 30 nM, whereas LTD4, diastereoisomers of LTD1, LTE4 and the end organ antagonist FPL 55712 were 150 to 700 fold less potent competitors than LTC4. These results provide evidence for specific, reversible, saturable, high affinity binding sites for [3H]-LTC4 in human fetal lung membranes. 相似文献
7.
In this work, the synthesis, crystal structure, characterization, and enzyme inhibition effects of the novel a series of 2-aminopyridine liganded Pd(II) N-heterocyclic carbene (NHC) complexes were examined. These complexes of the Pd-based were synthesized from PEPPSI complexes and 2-aminopyridine. The novel complexes were characterized by using 13C NMR, 1H NMR, elemental analysis, and FTIR spectroscopy techniques. Also, crystal structures of the two compounds were recorded by using single-crystal X-ray diffraction assay. Also, these complexes were tested toward some metabolic enzymes like α-glycosidase, aldose reductase, butyrylcholinesterase, acetylcholinesterase enzymes, and carbonic anhydrase I, and II isoforms. The novel 2-aminopyridine liganded (NHC)PdI2(2-aminopyridine) complexes (1a-i) showed Ki values of in range of 5.78 ± 0.33–22.51 ± 8.59 nM against hCA I, 13.77 ± 2.21–30.81 ± 4.87 nM against hCA II, 0.44 ± 0.08–1.87 ± 0.11 nM against AChE and 3.25 ± 0.34–12.89 ± 4.77 nM against BChE. Additionally, we studied the inhibition effect of these derivatives on aldose reductase and α-glycosidase enzymes. For these compounds, compound 1d showed maximum inhibition effect against AR with a Ki value of 360.37 ± 55.82 nM. Finally, all compounds were tested for the inhibition of α-glycosidase enzyme, which recorded efficient inhibition profiles with Ki values in the range of 4.44 ± 0.65–12.67 ± 2.50 nM against α-glycosidase. 相似文献
8.
The thermodynamics of formation for DIMBOA-Cu(II) complexes (where DIMBOA = 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-4H-one, a hydroxamic acid from maize) has been investigated in aqueous solutions by a potentiometric method. DIMBOA forms 1:1 and 1:2 chelates with Cu(II) at ionic strength 0.05 M (NaCl04). The stability constants measured were about 105 and 104 for the 1:1 and 1:2 complexes respectively, determined at 10, 20 and 30°. The contribution of ΔH and ΔS to the stability of complexes is examined and the pK values are compared with other ligands found in maize. Although DIMBOA has similar or higher constants to form copper complexes than other plant ligands, its possible role as a transport agent in maize remains to be established. 相似文献
9.
Charles S. Irving Bruce E. Hammer Steven S. Danyluk Peter D. Klein 《Journal of inorganic biochemistry》1980,13(2):137-150
13C Nuclear magnetic resonance chemical shifts, 1JC-C scalar coupling constants, spin-lattice relaxation times, and nuclear Overhauser effects were determined for taurine-[1, 2 13C] and a taurine-[1 13C] and taurine-[2 13C] mixture in the presence and absence of calcium. Ionization constants for taurine amino and sulfonic acid groups and chemical shifts of N-methylene and S-methylene carbons of the taurine cation, zwitterion, and anion were obtained from simultaneous least squares analysis of 13C titration curves of both taurine carbons. Comparison of taurine titration shifts to values for related compounds reveals some unusual electronic properties of the taurine molecule. Stability constants of 1:1 calcium complexes with taurine zwitterions and anions, as well as their 13C chemical shifts, were obtained by least squares analysis of titration curves measured in the presence of calcium. The stability constants of calcium-taurine complexes were significantly lower than previous values and led to estimates that only approximately one percent of intracellular calcium of mammalian myocardial cells would exist in a taurine complex. The implications of these results with respect to the effect of taurine on calcium ion flux are discussed. 相似文献
10.
Novel chiral Schiff base ligands (R)/(S)‐2‐amino‐3‐(((1‐hydroxypropan‐2‐yl)imino)methyl)‐4H‐chromen‐4‐one (L1 and L2) derived from 2‐amino‐3‐formylchromone and (R/S)‐2‐amino‐1‐propanol and their Cu(II)/Zn(II) complexes ( R1 , S1 , R2 , and S2 ) were synthesized. The complexes were characterized by elemental analysis, infrared (IR), hydrogen (1H) and carbon (13C) nuclear magnetic resonance (NMR), electrospray ionization‐mass spectra (ESI‐MS), and molar conductance measurements. The DNA binding studies of the complexes with calf thymus were carried out by employing different biophysical methods and molecular docking studies that revealed that complexes R1 and S1 prefers the guanine–cytosine‐rich region, whereas R2 and S2 prefers the adenine–thymine residues in the major groove of DNA. The relative trend in Kb values followed the order R1 S1 R2 S2 . This observation together with the findings of circular dichroic and fluorescence studies revealed maximal potential of (R)‐enantiomeric form of complexes to bind DNA. Furthermore, the absorption studies with mononucleotides were also monitored to examine the base‐specific interactions of the complexes that revealed a higher propensity of Cu(II) complexes for guanosine‐5′‐monophosphate disodium salt, whereas Zn(II) complexes preferentially bind to thymidine‐5′‐monophosphate disodium salt. The cleavage activity of R1 and R2 with pBR322 plasmid DNA was examined by gel electrophoresis that revealed that they are good DNA cleavage agents; nevertheless, R1 proved to show better DNA cleavage ability. Topoisomerase II inhibitory activity of complex R1 revealed that the complex inhibits topoisomerase II catalytic activity at a very low concentration (25 μM). Furthermore, in vitro antitumor activity of complexes R1 and S1 were screened against human carcinoma cell lines of different histological origin. Chirality 24:977–986, 2012. © 2012 Wiley Periodicals, Inc. 相似文献
11.
Development of new chemotherapeutic agents to treat microbial infections and recurrent cancers is of pivotal importance. Metal based drugs particularly ruthenium complexes have the uniqueness and desired properties that make them suitable candidates for the search of potential chemotherapeutic agents. In this study, two mixed ligand Ru(III) complexes [Ru(Cl)2(SB)(Phen] (RC-1) and [Ru(Cl)2(SB)(Bipy)] (RC-2) were synthesised and characterized by elemental analysis, IR, UV–Vis, 1H, 13C NMR spectroscopic techniques and their molecular structure was confirmed by X-ray crystallography. Antibacterial activity evaluation against two Gram-positive (S. pneumonia and E. faecalis) and four Gram-negative strains (P. aurogenosa, K. pneumoniae, S. enterica, and E. coli) revealed their moderate antibacterial activity with MIC value of ≥250 μg/mL. Anticancer activity evaluation against a non-small lung cancer cell line (H1299) revealed the tremendous anticancer activity of these complexes which was further validated by DNA binding and docking results. DNA binding profile of the complexes studied by UV–Visible and fluorescence spectroscopy showed an intercalative binding mode with CT-DNA and an intrinsic binding constant in the range of 3.481–1.015× 105 M−1. Both the complexes were also found to exert weak toxicity to human erythrocytes by haemolytic assay compared to cisplatin. Potential of these complexes as anticancer agents will be further delineated by in vivo studies. 相似文献
12.
EPR spectra at 4, 9 and 35 GHz of hydrogenase isolated from Chromatium vinosum have been compared. The spectra at 4 and 35 GHz confirmed our earlier conclusions, made from observations at 9 GHz (Albracht, S.P.J., Kalkman, M.L. and Slater, E.C. (1983) Biochim. Biophys. Acta 724, 309–316), that the irreversibly inactivated enzyme molecules in the preparation give rise to two EPR signals due to the independent non-interacting systems of Ni(III) and a |3Fe-xS| cluster. It was observed that intact enzyme molecules show a complex EPR spectrum caused by a spin-coupled pair of Ni(III) and a |4Fe-4S|3+ cluster. The interaction energy is so weak (approx. 0.01 cm?1) that the 35 GHz spectra of both the Ni(III) and the |4Fe-4S|3+ cluster have the appearance of rather normal spectra with additional splittings as a result of the spin-spin interaction. At lower microwave frequencies, the spectra become increasingly complex but phenomenologically they behave as expected for an exchange-coupled pair of dissimilar ions. The distance between the two spin systems is estimated to be at the most 1.2 nm. The spin-relaxation rate of the Ni(III) ion is dramatically enhanced as a result of the coupling to the rapidly relaxing Fe-S cluster. The g values and so presumably also the ligand fields of Ni in intact and irreversibly inactivated enzyme molecules are identical. This suggests that the specific coordination of the nickel in the enzyme is not the only requirement for activity with artificial electron donors or acceptors, and that the presence of a nearby, intact |4Fe-4S|3+(3+,2+) cluster might be another essential factor. From the g values and the probable function of Ni in the enzyme we propose, as a working hypothesis, that the nickel ion has five ligands provided by the protein in a square-pyramidal coordination. 相似文献
13.
Pyruvate dehydrogenase complex from higher plant mitochondria and proplastids: kinetics 总被引:2,自引:2,他引:0
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A steady-state kinetic analysis has been performed on the pyruvate dehydrogenase complex from pea (Pisum sativum L.) mitochondria and castor bean (Ricinus communis L.) proplastids. Substrate interaction kinetics for all substrates gave parallel lines consistent with a multisite ping-pong mechanism. Product inhibition studies showed uncompetitive inhibition between acetyl-CoA and pyruvate and competitive inhibition between NADH and NAD+, both of which are also consistent with this mechanism. In the mitochondrial complex, acetyl-CoA showed noncompetitive inhibition versus CoA which suggests that the intermediate complex is kinetically important in the lipoamide transacetylase component of this complex. In contrast, the proplastid complex showed competitive inhibition in this interaction. NADH is a noncompetitive inhibitor versus CoA in both complexes indicating that these complexes, like the mammalian complex, may have protein-protein interactions between the second and third enzymes of the complex. Since NADH also shows noncompetitive inhibition versus pyruvate, this interaction may extend to all components of the complex. Acetyl-CoA shows noncompetitive inhibition versus NAD+ which may also be a result of interaction between the second and third enzymes of the complex. The limiting Michaelis constants for substrates and the inhibitor constants for both complexes were determined. 相似文献
14.
Miral V. Lunagariya Khyati P. Thakor Bharat H. Pursuwani 《Nucleosides, nucleotides & nucleic acids》2013,32(8):455-483
AbstractSquare planar mononuclear platinum(II) complexes having general formula [Pt(Ln)Cl2], (where, Ln?=?L1–4) were synthesized with neutral bidentate heterocyclic 1,3,5-trisubstituted bipyrazole based ligands. The synthesized compounds were characterized by physicochemical method such as TGA, molar conductance, micro-elemental analysis and magnetic moment, and spectroscopic method such as, FT-IR, UV–vis, 1H NMR, 13C NMR and mass spectrometry. Biological applications of the compounds were carried out using in vitro brine shrimp lethality bioassay, in vitro antimicrobial study against five different pathogens, and cellular level cytotoxicity against Schizosaccharomyces pombe (S. Pombe) cells. Pt(II) complexes were tested for DNA interaction activities using electronic absorption titration, viscosity measurements study, fluorescence quenching technique and molecular docking assay. Binding constants (Kb) of ligands and complexes were observed in the range of 0.23–1.07?×?105?M?1 and 0.51–3.13?×?105?M?1, respectively. Pt(II) complexes (I–IV) display an excellent binding tendency to biomolecule (DNA) and possess comparatively high binding constant (Kb) values than the ligands. The DNA binding study indicate partial intercalative mode of binding in complex-DNA. The gel electrophoresis activity was carried out to examine DNA nuclease property of pUC19 plasmid DNA. 相似文献
15.
Umair S Knight JS Patchett ML Bland RJ Simpson HV 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》2012,161(3):255-260
The expression of glutamate dehydrogenase (GDH; EC 1.4.1.3) in L3 of the nematode Haemonchus contortus was confirmed by detecting GDH mRNA, contrary to earlier reports. The enzyme was active in both L3 and adult H. contortus homogenates either with NAD+/H or NADP+/H as co-factor. Although it was a dual co-factor GDH, activity was greater with NAD+/H than with NADP+/H. The rate of the aminating reaction (glutamate formation) was approximately three times higher than for the deaminating reaction (glutamate utilisation). GDH provides a pathway for ammonia assimilation, although the affinity for ammonia was low. Allosteric regulation by GTP, ATP and ADP of L3 and adult H. contortus and Teladorsagia circumcincta (Nematoda) GDH depended on the concentration of the regulators and the direction of the reaction. The effects of each nucleotide were qualitatively similar on the mammalian and parasite GDH, although the nematode enzymes were more responsive to activation by ADP and ATP and less inhibited by GTP under optimum assay condition. GTP inhibited deamination and low concentrations of ADP and ATP stimulated weakly. In the reverse direction, GTP was strongly inhibitory and ADP and ATP activated the enzyme. 相似文献
16.
A fully functional ornithine–glutamate–proline pathway was detected in L3 and adult Haemonchus contortus and Teladorsagia circumcincta, making the parasites capable of interconversion of these amino acids. Ornithine aminotransferase (OAT) (E.C. 2.6.1.13) was a reversible pyridoxal-5-phosphate (PLP)-dependent enzyme with an optimum pH 8.5. Hydroxylamine completely inhibited OAT activity in both parasites. For all five enzymes, substrate affinity was similar for each species and life cycle stage, the notable exceptions being the nearly 10-fold lower affinity for Δ1-pyrroline-5-carboxylate (P5C) of P5C reductase (E.C. 1.5.1.2) in adult T. circumcincta and about half for P5C for L3 H. contortus P5C dehydrogenase (E.C. 1.5.1.12). P5C synthase (E.C. 1.2.1.41) activity was similar with either NADPH or NADH as co-factor. Proline oxidase (E.C. 1.5.99.8) was a co-factor independent enzyme with an optimal pH 8.5. Despite similarities to those in the host, enzymes of this pathway may still be useful as control targets if they differ antigenically, as a supply of proline is necessary for cuticle formation. 相似文献
17.
Behafarid Ghalandari Atefeh Poursoleiman Mina Fekri Ali Komeili Adeleh Divsalar Mahboube Eslami Moghadam 《Journal of biomolecular structure & dynamics》2019,37(13):3422-3433
To perform biological evaluations of newly-designed Pt(II) and Pd(II) complexes, the present study was conducted with targeted protein human serum albumin (HSA) and HCT116 cell line as model of human colorectal carcinoma. The binding of Pt(II) and Pd(II) complexes to HSA was analyzed using fluorescence spectroscopy and molecular docking. The thermal stability and alterations in the secondary structure of HSA in the presence of Pt(II) and Pd(II) complexes were investigated using the thermal denaturation method and circular dichroism (CD) spectroscopy. The cytotoxicity of the Pt(II) and Pd(II) complexes was studied against the HCT116 cell line using MTT assay. The binding analysis revealed that the fluorescence findings were well in agreement with docking results such that there is only one binding site for each complex on HSA. Binding constants of 8.7?×?103 M?1, 2.65?×?103 M?1, 0.3?×?103 M?1, and 4.4?×?103 M?1 were determined for Pd(II) and Pt(II) complexes (I–IV) at temperature of 25?°C, respectively. Also, binding constants of 1.9?×?103 M?1, 15.17?×?103 M?1, 1.9?×?103 M?1, and 13.1?×?103 M?1 were determined for Pd(II) and Pt(II) complexes (I–IV) at temperature of 37?°C, respectively. The results of CD and thermal denaturation showed that the molecular structure of HSA affected by interaction with Pt(II) and Pd(II) complexes is stable. Cytotoxicity studies represented the growth suppression effect of the Pt(II) and Pd(II) complexes toward the human colorectal carcinoma cell line. Therefore, the results suggest that the new designed Pt(II) and Pd(II) complexes are well promising candidates for use in cancer treatment, particularly for human colorectal cancer.
Communicated by Ramaswamy H. Sarma 相似文献
18.
The escape of several enzymes from “ammonia catabolite repression” in gdhA? (NADP-linked glutamate-dehydrogenase-less) mutants, as well as in gdhCR mutants of Saccharomyces cerevisiae, does not involve glutamine synthetase, either as a positive or as a negative control element. A glutamine-synthetase-less mutant (gln?) was used in this demonstration.In addition to its derepressing effect on the NAD-linked glutamate dehydrogenase, the gdhCR mutation releases “nitrogen catabolite repression” on arginase and allatoinase, as well as glutamine repression on glutamine synthetase. A gdhCS mutation was used to demonstrate that these effects are not mediated through the NAD-linked glutamate dehydrogenase. 相似文献
19.
Jerzy Rogalski Janusz Szczodrak Andrzej Dawidowicz Zdzisław Ilczuk Andrzej Leonowicz 《Enzyme and microbial technology》1985,7(8):395-400
The major components of cellulase [see 1,4-(1,3;1,4)-β-d-glucan 4-glucanohydrolase, EC 3.2.1.4] and d-xylanase (see 1,4-β-d-xylan xylanohydrolase, EC 3.2.1.8) complexes have been immobilized on glass beads activated by 3-aminopropyltriethoxysilane or 3-glycidoxypropyltrimethoxysilane. The final preparations contained over 20 mg protein g?1 glass beads. The activity retained was 71.6–98.1% for cellulase complexes and 81–100% for d-xylanase complexes. The immobilization of the enzymes spread their optimum pH range. Cellulose and d-xylan were quantitatively hydrolysed by the immobilized enzymes. The major reaction products were identified as a d-glucose and d-xylose respectively. 相似文献
20.
The electron transfer reactions of horse heart cytochrome c with a series of amino acid-pentacyanoferrate(II) complexes have been studied by the stopped-flow technique, at 25°C, μ = 0.100, pH 7 (phosphate buffer). A second-order behavior was observed in the case of the Fe(CN)5 (histidine)3? complex, with k = 2.8 x 105 M?1 sec?1. For the Fe(CN)5 (alanine)4? and Fe(CN)5(L-glutamate)5? complexes, only a minor deviation of the second-order behavior, close to the experimental error (k = 3.2 × 105 and 1.6 x 105 M?1 sec?1, respectively) was noted at high concentrations of the reactants (e.g., 6 × 10?4 M). The results are in accord with recent work on the Fe(CN)64?/cytochrome c system demonstrating weak association of the reactants. The calculated self-exchange rate constants including electrostatic interactions for the imidazole,L -histidine, 4-aminopyridine, glycinate, β-alaninate, andL-glutamate pentacyanoferrate(II) complexes were 3.3 × 105, 3.3 × 105, 2.8 × 106,4.1 × 102,5.5 × 102, and 6.0 M?1 sec?1, respectively. Marcus theory calculations for the cytochrome c reactions were interpreted in terms of two nonequivalent binding sites for the complexes, with the metalloprotein self-exchange rate constants varying from 104 M?1 sec?1 (histidine, imidazole, and 4-aminopyridine complexes) to 106 M?1 sec ?1 (glycinate, β-alaninate, and L-glutamate complexes). 相似文献