首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
The mechanism of activation of alkaline phosphatase (EC 3.1.3.1) from pig kidney by Mg2+ ions was investigated with the aid of kinetic measurements. Mg2+ ions are essential for enzyme activity. The following model (Scheme 1 of the text) for the reaction of enzyme, substrate and Mg2+ ions was derived: [Formula: see text] The binding of the substrate to the enzyme is independent of the binding of the activator, and vice versa. Mg2+ must therefore play a part in the substrate decomposition. It is not possible to determine whether the Mg2+ ions are involved directly in the catalytic process, or whether they act as regulatory effectors. Because of the strong affinity existing between the alkaline phosphatase and Mg2+, it is necessary to adjust the metal-ion concentration with the aid of a metal buffer. In the Appendix the necessary equations are derived for calculating the concentration of free metal ions in a system with several different metal ions. A FORTRAN IV program for solving these equations and for graphic presentation of the results has been deposited as Supplementary Publication SUP 50030 at the British Library (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS 23 7 BQ, U.K., from whom copies may be obtained on the terms indicated in Biochem. J. (1973), 131, 5.  相似文献   

2.
The amino acid sequence of the plastocyanin from French bean (Phaseolus vulgaris) was determined. The protein consists of a single polypeptide chain of 99 residues, and the sequence was determined by characterization of CNBr, tryptic, chymotryptic and thermolysin peptides. When the sequence is compared with that from the plastocyanin of the unicellular green alga Chlorella fusca, the French-bean protein shows the deletion of the N-terminal residue, a two residue insertion and 53 identical residues. Detailed evidence for the sequence of the protein has been deposited as Supplementary Publication SUP 50037 (16pp., 1 microfiche) at the British Library (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1973) 131, 5.  相似文献   

3.
The amino acid sequence of spinach (Spinacea oleracea L., var. Monster Viroflay) cytochrome c was determined on 1μmol of protein. The molecule consists of 111 residues and is homologous with other mitochondrial cytochromes c. Experimental details are given in a supplementary paper that has been deposited as Supplementary Publication SUP 50013, at the National Lending Library for Science and Technology, Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1973), 131, 5.  相似文献   

4.
The cytochrome complement of Methylophilus methylotrophus and its respiratory properties were determined during batch culture and in continuous culture under conditions of methanol-, nitrogen- and O2-limitation. About 35% of the cytochrome c produced by the bacteria was released into the growth medium, and of the remaining cytochrome c about half was membrane-bound and half was soluble. Two cytochromes c were always present on membranes (redox potentials 375mV and 310mV), and these probably correspond to the soluble cytochromes c described previously [Cross & Anthony (1980) Biochem. J. 192, 421–427]. A third minor component of cytochrome c (midpoint potential 356mV) was only detected on membranes of methanol-limited bacteria. M. methylotrophus always contained two membrane-bound cytochromes b with α-band absorption maxima of about 556 and 563nm (measured at room temperature) and midpoint potentials of 110 and 60mV respectively. There appeared to be relatively more of the cytochrome b563 in methanol-limited bacteria. A third b-type cytochrome with an α-band absorption maximum at 558 (at 77K) reacted with CO and had a high midpoint redox potential (260mV); it is thus a potential oxidase and hence is called cytochrome o. The roles of these cytochromes in electron transport were confirmed by investigating the patterns of respiratory inhibition. It is proposed that two cytochromes are physiological oxidases: cytochrome a+a3, which is present only in methanol-limited conditions, and the cytochrome o, which is induced 10-fold in conditions of methanol excess. Schemes for electron transport from methanol and NAD(P)H to O2 in M. methylotrophus under various limitations are proposed. Spectra and potentiometric titrations of cytochromes in whole cells and membranes of M. methylotrophus grown under various nutrient limitations have been deposited as Supplementary Publication SUP 50111 (10 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978) 169, 5.  相似文献   

5.
In rabbit heart, results show that two isoenzymes of hexokinase (HK) are present. The enzymatic activity associated with mitochondria consists of only one isoenzyme; according to its electrophoretic mobility and its apparent Km for glucose (0.065 mm), it has been identified as type I isoenzyme. The bound HK I exhibits a lower apparent Km for ATPMg than the solubilized enzyme, whereas the apparent Km for glucose is the same for bound and solubilized HK. Detailed studies have been performed to investigate the interactions which take place between the enzyme and the mitochondrial membrane. Neutral salts efficiently solubilize the bound enzyme. Digitonin induces only a partial release of the enzyme bound to mitochondria; this result could be explained by the existence of contacts between the outer and the inner mitochondrial membranes [C. R. Hackenbrock (1968)Proc. Natl. Acad. Sci. USA61, 598–605]. Furthermore, low concentrations (0.1 mm) of glucose 6-phosphate (G6P) or ATP4? specifically solubilize hexokinase. The solubilizing effect of G6P and ATP4?, which are potent inhibitors of the enzyme, can be prevented by incubation of mitochondria with Pi or Mg2+. In addition, enzyme solubilization by G6P can be reversed by Mg2+ only when the proteolytic treatment of the heart homogenate is omitted during the course of the isolation of mitochondria. These results concerning the interaction of rabbit heart hexokinase with the outer mitochondrial membrane agree with the schematic model proposed by Wilson [(1982) Biophys. J.37, 18–19] for the brain enzyme. This model involves the existence of two kinds of interactions between HK and mitochondria; a very specific one with the hexokinase-binding protein of the outer mitochondrial membrane, which is suppressed by glucose 6-phosphate, and a less specific, cation-mediated one.  相似文献   

6.
The genome of the cabbage clubroot pathogen Plasmodiophora brassicae Woronin 1877 (Cercozoa, Rhizaria, SAR), possesses two expressed genes encoding the P450s that are phylogenetically related to the enzymes of oxylipin biosynthesis of the CYP74 clan. The cDNA of one of these genes (CYP50918A1) has been expressed in E. coli. The preferred substrate for the recombinant protein, the 13-hydroperoxide of α-linolenic acid (13-HPOT), was converted to the novel heterobicyclic oxylipins, plasmodiophorols A and B (1 and 2) at the ratio ca. 12:1. Compounds 1 and 2 were identified as the substituted 6-oxabicyclo[3.1.0]hexane and 2-oxabicyclo[2.2.1]heptane (respectively) using the MS and NMR spectroscopy, as well as the chemical treatments. The 18O labelling experiments revealed the incorporation of a single 18O atom from [18O2]13-HPOT into the epoxide and ether functions of products 1 and 2 (respectively), but not into their OH groups. In contrast, the 18O from [18O2]water was incorporated only into the hydroxyl functions. One more minor polar product, plasmodiophorol C (3), identified as the cyclopentanediol, was formed through the hydrolysis of compounds 1 and 2. Plasmodiophorols A–C are the congeners of egregiachlorides, hybridalactone, ecklonialactones and related bicyclic oxylipins detected before in some brown and red algae. The mechanism of 13-HPOT conversions to plasmodiophorols A and B involving the epoxyallylic cation intermediate is proposed. The hydroperoxide bicyclase CYP50918A1 is the first enzyme controlling this kind of fatty acid hydroperoxide conversion.  相似文献   

7.
The reaction kinetics of acetyl-coenzyme A carboxylase purified from developing castor oil seeds have been examined. On the basis of the substrate interaction and product inhibition results, a hybrid ping-pong mechanism is proposed. This type of mechanism demands that the active site of the enzyme be separated into two functionally distinct catalytic sites. The carboxybiotin intermediate formed at one site by the hydrolysis of ATP swings to the second site where acetyl-CoA is carboxylated to form malonyl-CoA. This hybrid rapid-equilibrium random bi bi uni uni ping-pong mechanism which includes the formation of three abortive complexes, E · HCO3? · ADP, E · HCO3? · Pi and E · Pi · Pi, is analogous to the hybrid ping-pong mechanism previously described for methylmalonyl-CoA transcarboxylase (D. B. Northrop (1969) J. Biol. Chem., 244, 5808) and pyruvate carboxylase (R. E. Barden, C-H. Fung, M. F. Utter, and M. C. Scrutton (1972) J. Biol. Chem., 247, 1323).  相似文献   

8.
《Inorganica chimica acta》1986,114(2):151-158
CoX2(NO)(PMe3)2 complexes (X = Cl, Br, I, NO2) exhibit markedly different ν(NO) stretching frequencies and different geometries. The structure of CoI2(NO)(PMe3)2 (1) and CoCl2(NO)(PMe3)2 (2) have been determined by X-ray diffraction. Both crystallize in the orthorhombic system, Pnma space group with four molecules in a cell of the following dimensions: for 1, a = 10.497(2), b = 10.694(2), c = 13.975(2) Å, ν= 1568.8, Å3; for 2, a = 9.607(2), b = 10.689(2), c = 13.512(3) Å, ν= 1387.5 Å3. The structures were refined to conventional R values of R = 0.040 from 1630 reflections for 1 and R = 0.033 from 976 reflections for 2. In both cases, the coordination geometry about the five-coordinate cobalt atom is approximately trigonal bipyramidal, with the NO group sharing the equatorial positions with the halide ligands. Structure 2 is disordered, which prevents any precise structural characterization. In (1), the CoNO angle is 179.2(19)° and the Co NO distance is 1.728(23) Å; v(NO) is 1753 cm−1. CoCl2(NO)(PMe3)3 shows a v(NO) vibration at 1637 cm−1. Co(NO2)2(NO)(PMe3)2 with v(NO) = 1658 cm−1 has been proposed as a square pyramidal structure with a bent apical CoNO. These differences in NO stretching frequencies and geometries are discussed.  相似文献   

9.
Anti-melanogenesis effects of silymarin from milk thistle have been reported recently, but detailed tyrosinase inhibition properties of individual components have not been investigated. This study purported to substantiate tyrosinase inhibition and its mechanism based on a single metabolite. The responsible components for tyrosinase inhibition of target source were found out as flavonolignans which consist of isosilybin A (1), isosilybin B (2), silydianin (3), 2,3-dihydrosilychristin (4), silychristin A (5), silychristin B (6) and silybin (7), respectively. The isolated flavonolignans (17) inhibited both monophenolase (IC50 = 1.7–7.6 µM) and diphenolase (IC50 = 12.1–44.9 µM) of tyrosinase significantly. Their inhibitions were 10-fold effective in comparison with their mother skeletons (810). Inhibitory functions were also proved by HPLC analysis using N-acetyl-l-tyrosine as substrate. The predominant formation of Emet·I was confirmed from a long prolongation of lag time and a decrease of the static state activity of the enzyme. All tested compounds had a significant binding affinity to tyrosinase with KSV values of 0.06–0.27 × 104 L·mol−1, which are well correlated with IC50s. In kinetic study, all flavonolignan (17) were mixed type I (KI < KIS) inhibitors, whereas their mother skeletons (810) were competitive ones. The UPLC-ESI-TOF/MS analysis showed that the isolated inhibitors are the most abundant metabolites in the target plant.  相似文献   

10.
γ-lrradiation of crystalline β-d-fructose yields 6-deoxy-d-threo-2,5-hexodiulose (2) via a chain reaction. The initial G-value at 25° is 38. With decreasing temperature, G(2) decreases strongly; however, no change in G(2) is observed on going to higher temperatures. G(2) is independent of dose rate, but decreases with increasing dose. A mechanism for the formation of 2 is proposed. Although G(2) decreases with increasing dose, γ-irridiation of d-fructose is a convenient method for obtaining 2 on a preparative scale. At a dose of 1021 eV.g?1, d-fructose is converted into ~6% of 2.  相似文献   

11.
The amino acid sequence of cytochrome c from Allium porrum L. (leek)   总被引:3,自引:3,他引:0  
The amino acid sequence of leek cytochrome c was determined with 0.4μmol of protein. The sequence was deduced solely from a chymotryptic digest. The cytochrome was homologous with other plant cytochromes c of mitochondrial origin. Leek cytochrome c has an N-acetylated `tail' as compared with mammalian cytochrome c, and two residues of ε-N-trimethyl-lysine. Unlike other plant cytochromes c, leek cytochrome c has glutamic acid or glutamine in position 11, leucine in position 20 and alanine in position 51. 4-Hydroxyproline partially substitutes for proline in position 79. Experimental details are given in a supplementary paper that has been deposited as Supplementary Publication SUP 50012, at the National Lending Library for Science and Technology, Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1973) 131, 5.  相似文献   

12.
《Carbohydrate research》1987,166(1):19-25
A single crystal of 3-O-(2,3-anhydro-4-deoxy-α-l-lyxo-hexopyranosyl)-1,2:5,6-di-O-isopropylidene-α-d-glucofuranose (1), obtained from its 6-acetate, has been investigated by X-ray diffraction methods. Compound 1 crystallises in the orthorhombic system, space group P21212P1, with cell dimensions a = 8.556(1), b = 12.303(1), and c = 18.397(1) Å. An almost ideal half-chair conformation 5Ho was found for the 2,3-anhydropyranose moiety of 1.  相似文献   

13.
The amino acid sequence of the major β-chain, IIβ, from rat haemoglobins was established with an automated sequencer. Amino acid heterogeneities were found that appear to result from allelic variation at particular residues. We applied several new or unusual techniques in determining the sequence: (1) reaction of the polypeptide with dansylaziridine for detection of cysteine; (2) blockage of the N-terminal residue and the ε-amino group of lysine residues with 1-fluoro-2-nitro-4-trimethylammoniobenzene iodide and subsequent identification of the modified lysine phenylthiohydantoin by absorbance at 420nm; (3) identification of histidine phenylthiohydantoin by its blue fluorescence under long-wave u.v. light; (4) cleavage of the chain into two or three fragments and subsequent sequencing without purification [a detailed statement giving the major phenylthiohydantoins assigned at each step for each sequence run before their alignment in individual sequences has been deposited as Supplementary Publication SUP 50084 (10 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978) 169, 5]; (5) separation of fragments produced by CNBr cleavage by cation-exchange chromatography; (6) peptide sequencing after attachment of the peptide to cytochrome c. The amino acid sequence was confirmed by amino acid compositions of the complete chain, of CNBr fragments 1 and 3, and of 11 purified tryptic peptides.  相似文献   

14.
The crystal structures of two modifications of gadoliniumdicyclopentadienidebromide, [Gd(C5H5)2Br]2 (I) and 1[Gd(C5H5)2Br] (II) have been determined from X-ray diffraction data. I crystallizes in the [Sc(C5H5)2Cl]2-type structure, space group P21/c, with a=14.110(3), b=16.488(3), c= 13.765(3) Å, β=93.25(2)°, V=3197(2) Å3, and Dc= 2.289 g cm−3 for Z=6 molecules. II crystallizes in space group P21/c with a=5.946(7), b=8.447(5), c=20.239(9) Å, β=90.11(4)°, V=1020(2) Å3, Dc=2.392 g cm−3 for Z=4 formula units. The structures have been refined by full matrix least-squares techniques to conventional R factors of 0.034 for 3014 (I) and 1964 (II) reflections (with I>2σ(I)). I consists of dimers with two bromine bridges (mean GdBr 2.872 Å). II has a double chain structure with alternating juxtaposition of gadolinium and bromine atoms (GdBr 2.912 Å (once) and 3.133 Å (twice)). The arrangement of the C5H5 groups with regard to the metal η5 fashion) is nearly identical in I and II (mean GdC 2.63(1) Å (I) and 2.62(1) Å (II)). Single crystals of I and II are obtained by sublimation at different temperatures. The formation of both modifications is discussed as to its dependence on the state of the gaseous phase equilibrium [Gd(C5H5)2Br]2 ⇄ 2Gd(C5H5)2Br. Obviously, I crystallizes from gaseous phase dimers while II forms from the monomers.  相似文献   

15.
Methylmercury(II) and mercury(II) complexes of imidazole (1), 1-methylimidazole (2), and the 1,3-dimethylimidazolium ion (3) have been prepared in aqueous or ethanolic solution. Elemental analysis and 1H nmr spectroscopy have been used to characterize the complexes. The MeHg (Me = methyl) binding sites have been identified as N1, N3 (1), N3, C2 (2), and C2 (3). Reaction with HgO leads to the formation of Hg-bridged complexes of the type Im-Hg-Im, (Im = imidazole), where bonding occurs through N1 (1) and C2 (3); the latter is also formed as a result of symmetrization of the C2-bound MeHg complex. The formation of the C2-bound (carbene) complexes is discussed in terms of the increased acidity of the C2 proton resulting from coordination of an electrophilic species at N3. Based on electrostatic considerations, there appears to be a “minimum degree of activation” required before C2 bonding can occur, which explains the lack of this coordination mode in 1. 199Hg-1H spin-spin coupling (4J) is observed for C-bound mercury, but not for N-bound mercury, which is interpreted in terms of a decreased ligand exchange rate in the former case, due to the greater stability of the Hg-C bond. 2J coupling constants measured in (CD3)2SO for a number of MeHg complexes of heterocyclic ligands (including the imidazoles of the present study) correlate well with the ligand pKa (25°C, aqueous solution), according to 2J = ?3.88 pKa + 248.5. Results in the present work are discussed in relation to our previous work with nucleosides. The significance of the results to biological systems is considered.  相似文献   

16.
Protein tyrosine phosphatase 1B (PTP1B) is a validated target for developing antiobesity, antidiabetic and anticancer drugs. Over the past years, several inhibitors of PTP1B have been discovered; however, none has been approved by the drug regulatory agencies. Interestingly, the research programs focused on discovering PTP1B inhibitors typically use truncated structures of the protein (PTP1B1-300, 1–300 amino acids), leading to the loss of valuable information about the inhibition and selectivity of ligands and repeatedly misleading the optimization of putative drug leads. Up to date, only six inhibitors of the full-length protein (hPTP1B1-400), with affinity constants ranging from 1.3 × 104 to 3.3 × 106 M−1, have been reported. Towards the discovery of new ligands of the full-length human PTP1B (hPTP1B1-400) from natural sources, herein we describe the isolation of a γ-lactone (1, butyrolactone I) from the fungus Aspergillus terreus, as well as the semisynthesis, inhibitory properties (in vitro and in silico), and the structure-activity relationship of a set of butyrolactone derivatives (1 and 2, and 6–12) as hPTP1B1-400 inhibitors, as well as the affinity constant (ka = 2.2 × 105 M−1) of the 1-hPTP1B1400 complex, which was determined by fluorescence quenching experiments, after the inner filter effect correction.  相似文献   

17.
A series of mononuclear manganese(III) complexes of formulae [Mn(L)(X)(H2O)] (1-13) and [Mn(L)(X)] (14-17) (X = ClO4, F, Cl, Br, I, NCS, N3), derived from the Schiff bases of 5-bromosalicylaldehyde and different types of diamine (1,2-diaminoethane, 1,2-diaminopropane, 1,3-diaminopropane and 1,4-diaminobutane), have been synthesized and characterized by the combination of IR, UV-Vis spectroscopies, cyclic voltammetry and by X-ray crystallography. The redox properties of all the manganese(III) complexes show grossly identical features consisting of a reversible or quasireversible MnIII/MnII reduction. Besides MnIII/MnII reduction, the complexes 4, 5, 10, 13 and 16 also show reversible or quasireversible MnIII/MnIV oxidation. A linear correlation has been found for the complexes 5, 7, 11 and 13 [Mn(L2)(X)(H2O)] (X = F, Cl, Br, I) when E1/2 [MnIII/MnII] is plotted against Mulliken electronegativities (χM). The effect of the flexibility of the ligand on redox potential has been studied. It has been observed that the manganese(II) state is stabilized with increasing flexibility of the ligand environment. The crystal structure of 6 shows an octahedral geometry.  相似文献   

18.
A series of mononuclear iron(III) complexes with containing phenolate donor of substituted-salicylaldimine based ligands [Fe(L1)(TCC)] · CH3OH (1), [Fe(L2)(TCC)] · CH3OH (2), [Fe(L3)(TCC)] (3), and [Fe(L4)(TCC)] (4) have been prepared and studied as functional models for catechol dioxygenases (H2TCC = tetrachlorocatechol, or HL1 = N′-(salicylaldimine)-N,N-diethyldiethylenetriamine, HL2 = N′-(5-Br-salicylaldimine)-N,N-diethyldiethylenetriamine, HL3 = N′-(4,6-dimethoxy-salycyl-aldimine)-N,N-diethyl-diethylenetriamine, HL4 = N′-(4-methoxy-salicylaldimine)-N,N-diethyl-diethylenetriamine). They are structural models for inhibitors of enzyme-substrate adducts from the reactions of catechol 1,2-dioxygenases. Complexes 1-4 were characterized by spectroscopic methods and X-ray crystal structural analysis. The coordination sphere of Fe(III) atom of 1-4 is distorted octahedral with N3O3 donor set from the ligand and the substrate TCC occupying cis position, and Fe(III) is in high-spin (S = 5/2) electronic ground state. The in situ prepared iron(III) complexes without TCC, [Fe(L1)Cl2], [Fe(L2)Cl2], [Fe(L3)Cl2], and [Fe(L4)Cl2] are reactive towards intradiol cleavage of the 3,5-di-tert-butylcatechol (H2DBC) in the presence of O2 or air. The reaction rate of catechol 1,2-dioxygenase depends on the redox potential and acidity of iron(III) ions in complexes as well as the substituent effect of the ligands. We have identified the reaction products and proposed the mechanism of the reactions of these iron(III) complexes with H2DBC with O2.  相似文献   

19.
The Raman spectra of Va-, Vhh-, and B-amylose have been recorded, and are interpreted in terms of the proposed mechanism for conversion from the V- into the B-form. Lines occurring at 1263 and 946cm-1 with V-amylose shift to 1254 and 936 cm-1 on conversion into the B-form; at the same time intensity changes are observed for the lines at 2940 and 1334 cm-1. These effects are consistent with the mechanism proposed for V→B conversion, involving an extension of the helix and changes in the intramolecular hydrogen-bonding. In addition, the spectra of amylose dissolved in aqueous salt solution and in methyl sulfoxide have been recorded. The results indicate that amylose does not adopt the V-conformation in methyl sulfoxide solution.  相似文献   

20.
The reaction of the dimeric zinc(II) chelates of the type I (R1 = R2 = CH3, R1 = H, R2 = Ph) with pyridine, 2-methylpyridine, 3-methylpyridine and 4-methylpyridine afforded the monomeric monobase adducts. The isolated adducts were characterized by their electronic and 1H NMR spectra, and a five coordinate square pyramidal structure was tentatively assigned for these adducts.The adduct formation reaction was followed spectrophotometrically and the reaction kinetics were studied using a stopped flow technique. From the available kinetic data, as well as the measured activated parameters (ΔH#, ΔS#), a mechanism for the adduct formation reaction is proposed.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号