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1.
Putrescine N-methyltransferase (PMT) catalyses S-adenosylmethionine (SAM)-dependent methylation of putrescine in tropane alkaloid biosynthesis. PMT presumably evolved from the ubiquitous spermidine synthase (SPDS). SPDS protein structure suggested that only few amino acid exchanges in the active site were necessary to achieve PMT activity. Protein modelling, mutagenesis, and chimeric protein construction were applied to trace back evolution of PMT activity from SPDS. Ten amino acid exchanges in Datura stramonium SPDS dismissed the hypothesis of facile generation of PMT activity in existing SPDS proteins. Chimeric PMT and SPDS enzymes were active and indicated the necessity for a different putrescine binding site when PMT developed. 相似文献
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Trigonelline is a major component in coffee seeds and may contribute to the bitter taste of the resultant beverage. To determine the trigonelline biosynthetic pathway in coffee fruits, we investigated the metabolic fate of [carboxyl-14C]nicotinic acid riboside and in situ activity of related enzymes. Exogenously supplied [carboxyl-14C]nicotinic acid riboside was rapidly converted to nicotinic acid mononucleotide and was utilized for NAD synthesis. Nicotinic acid riboside was also used for trigonelline synthesis, but this process took longer than NAD synthesis. These results indicate that an efficient nicotinic acid riboside salvage system functions in coffee fruits, and that trigonelline is synthesized mainly from nicotinic acid produced by the degradation of NAD. 相似文献
4.
Gordana P. Vasi? Ivana D. Radojevi? Ljiljana R. ?omi? Sre?ko R. Trifunovi? 《Inorganica chimica acta》2010,363(13):3606-3610
Three new ligands and their palladium(II) complexes of general formula [PdCl2(R2-S,S-eddp)] (R = n-propyl, n-butyl and n-pentyl) have been synthesized and characterized by microanalysis, infrared and 1H and 13C NMR spectroscopy. Antimicrobial activity of these ligands and complexes was tested by microdilution method and both minimal inhibitory and microbicidal concentration were determined. These tested complexes demonstrated the significant antifungal activity against pathogenic fungi Aspergillus flavus and Aspergillus fumigatus. On the other hand, these complexes demonstrated moderate antibacterial activity. 相似文献
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A series of palladium complexes, trans-[1-(R)-pz3,5-Me2]2PdCl2 {R = CH2CONH(2,6-i-Pr2-C6H3) (1b) and 2-(OH)-C6H10 (2b)}, supported over N/O-functionalized pyrazole derived ligands effectively catalyzed the more challenging Suzuki-Miyaura cross-coupling of a variety of activated aryl chlorides with phenyl boronic acid in air in a mixed-aqueous medium (DMF:H2O, v/v = 9:1) in moderate to excellent yields. Besides the commonly encountered Csp2-Csp2 coupling, the 1b and 2b precatalysts also catalyzed the relatively difficult Csp2-Csp3 coupling of benzyl chloride with phenyl boronic acid. The 1b and 2b complexes were synthesized by the direct reaction of the respective N/O-functionalized pyrazolyl ligands, 1a and 2a, with (COD)PdCl2 in 62-66% yields. The stability of the pyrazole-palladium interaction in the 1b and 2b complexes has been attributed to the deeply buried Npyrazole-Pd interaction as evidenced from the density functional theory (DFT) studies. 相似文献
7.
The reactions of [PtMe3(OAc)(bpy)] (4) with the N,S and S,S containing heterocycles, pyrimidine-2-thione (pymtH), pyridine-2-thione (pytH), thiazoline-2-thione (tztH) and thiophene-2-thiol (tptH), resulted in the formation of the monomeric complexes [PtMe3(-κS)(bpy)] ( = pymt, 5; pyt, 6; tzt, 7; tpt, 8), where the heterocyclic ligand is coordinated via the exocyclic sulfur atom. In contrast, in the reactions of [PtMe3(OAc)(Me2CO)x] (3, x = 1 or 2) with pymtH, pytH, tztH and tptH dimeric complexes [{PtMe3(μ-)}2] (μ- = pymt, 9; pyt, 10; tzt, 11) and the tetrameric complex [{PtMe3(μ3-tpt-κS)}4] (12), respectively, were formed. The complexes were characterized by microanalyses, 1H and 13C NMR spectroscopy and negative ESI-MS (12) measurements. Single-crystal X-ray diffraction analysis of [PtMe3(pymt-κS)(bpy)] (5) exhibited a conformation where the pymt ligand lies nearly perpendicular to the complex plane above the bpy ligand that was also confirmed by quantum chemical calculations on the DFT level of theory. 相似文献
8.
The new N,N,O heteroscorpionate ligand 3,3-bis(1-vinylimidazol-2-yl)propionic acid (Hbvip) (5) was synthesised in five steps starting from 1-vinylimidazole. This ligand is closely related to 3,3-bis(1-methylimidazol-2-yl)propionic acid (Hbmip), but contains two vinyl linker groups which can be used for radical-induced polymerisation reactions. The κ3-N,N,O coordination behaviour of 5 was proven by the synthesis of the tricarbonyl complexes [Re(bvip)(CO)3] (6), [Mn(bvip)(CO)3] (7) and [Cu(bvip)2] (8). To obtain good yields of 6, it was synthesised in water instead of THF. The ligand as well as all three complexes were characterised by X-ray crystallography. Copolymerisation of 5 with pure methyl methacrylate (MMA) or a combination of MMA and ethylene glycol dimethacrylate (EGDMA) led to the solid phases P1 and P2. Polymer-bound rhenium and manganese tricarbonyl complexes could be obtained by the reaction of deprotonated P1 with [MBr(CO)5] (M = Re, Mn) and also by copolymerisation of 6 and 7 with MMA. In both cases, the facial tripodal binding behaviour was evidenced by IR spectra of the polymers. Furthermore, the content of metal incorporated in the polymers was determined by elemental analysis, AAS or ICP-OES measurements. Reaction of the deprotonated solid phase P1 with copper(II) chloride led to a blue solid-phase (P1-Cu). The UV-Vis absorption maximum of P1-Cu is found at 615 nm, which is almost identical to that found for 8. Thereby, it seems likely that P1 is flexible enough to form bisligand complexes with copper(II). This means that the copper centres act as a kind of crosslinking agents. In contrast, the heterogeneous reaction of P2 with copper(II) chloride yielded a lime green solid phase (P2-Cu). The bathochromic shift of the absorption maximum by 102 nm suggests one-sided bound copper centres. 相似文献
9.
The metabolic fate of [carbonyl-14C]nicotinamide was surveyed in leaf disks of seven mangrove species, Bruguiera gymnorrhiza, Rhizophora stylosa, Kandeliaobovata, Sonneratia alba, Pemphis acidula, Lumnitzera racemosa and Avicennia marina, with and without 250 mM NaCl. Uptake of [14C]nicotinamide by leaf disks was stimulated by 250 mM NaCl in K. candel, R. stylosa, A. marina and L. racemosa. [Carbonyl-14C]nicotinamide was converted to nicotinic acid and was utilised for the synthesis of nucleotides and nicotinic acid conjugates. Formation of nicotinic acid by the deaminase reaction was rapid; there was little accumulation of nicotinamide in the disks 3 h after administration. Radioactivity from [carbonyl-14C]nicotinamide was incorporated into pyridine nucleotides (mainly NAD and NADP) in all mangrove leaves, and the rates varied from 2% (in L. racemosa) to 15% (S. alba) of the total radioactivity taken up. NaCl generally reduced nicotinic acid salvage for NAD and NADP. In all mangrove leaf disks, the most heavily labelled compounds (up to 70% of total radioactivity) were trigonelline (N-methylnicotinic acid) and/or nicotinic acid N-glucoside. Trigonelline was formed in all mangrove plants, but N-glucoside synthesis was found only in leaves of A. marina and K. obovata. In A. marina, incorporation of radioactivity into N-glucoside (51%) was much greater than incorporation into trigonelline (2%). In general, NaCl stimulates the synthesis of these pyridine conjugates. The rate of decarboxylation of nicotinic acid in roots of A. marina seedlings was much greater than for the corresponding reaction observed in leaves. 相似文献
10.
Salyan ME Pedicord DL Bergeron L Mintier GA Hunihan L Kuit K Balanda LA Robertson BJ Feder JN Westphal R Shipkova PA Blat Y 《Analytical biochemistry》2006,349(1):112-117
Methyltransferases form a large class of enzymes, most of which use S-adenosylmethionine as the methyl donor. In fact, S-adenosylmethionine is second only to ATP in the variety of reactions for which it serves as a cofactor. Several methods to measure methyltransferase activity have been described, most of which are applicable only to specific enzymes and/or substrates. In this work we describe a sensitive liquid chromatography/mass spectroscopy-based methyltransferase assay. The assay monitors the conversion of S-adenosylmethionine to S-adenosylhomocysteine and can be applied to any methyltransferase and substrate of interest. We used the well-characterized enzyme catechol O-methyltransferase to demonstrate that the assay can monitor activity with a variety of substrates, can identify new substrates, and can be used even with crude preparation of enzyme. Furthermore, we demonstrate the utility of the assay for kinetic characterization of enzymatic activity. 相似文献
11.
Oliver M.T. Pearce 《Carbohydrate research》2010,345(9):1225-6005
N-Glycolylneuraminic acid (Neu5Gc) is a non-human sialic acid, which may play a significant role in human pathologies, such as cancer and vascular disease. Further studies into the role of Neu5Gc in human disease are hindered by limited sources of this carbohydrate. Using a chemo-enzymatic approach, Neu5Gc was accessed in six steps from glucose. The synthesis allows access to gram-scale quantities quickly and economically and produces Neu5Gc in superior quality to commercial sources. Finally, we demonstrate that the synthesized Neu5Gc can be incorporated into the cell glycocalyx of human cells, which do not naturally synthesize this sugar. The synthesis produces Neu5Gc suitable for in vitro or in vivo use. 相似文献
12.
Pseudomonas aeruginosa K187, a protease- and chitinase-producing bacterium, exhibited protease and chitinase activity after three and five days of incubation, respectively. The protease and chitinase were both produced by using 1% squid pen powder (SPP) (w/v) as sole carbon and nitrogen source. After fermentation, the deproteinization rate of the recovered squid pen gradually increased up to 68% on the fourth day. After five days of fermentation, the production of GlcNAc, (GlcNAc)2, (GlcNAc)3, (GlcNAc)4 and (GlcNAc)5 were 1.18 mg/mL, 0.76 mg/mL, 1.02 mg/mL, 0.93 mg/mL and 0.90 mg/mL, respectively. The culture supernatant of K187 also exhibited activity of enhancing vegetable growth. For Brassica chinensis Linn treated with the fifth day culture supernatant, the total weight and total length increased up to 529% and 148%, respectively, compared to the control group. With this method, the production of protease, chitinase, N-acetyl chitooligosaccharides and biofertilizers may be useful for biological applications. 相似文献
13.
Marietta Tóth 《Carbohydrate research》2010,345(1):163-167
(2′,3′-O-Isopropylidene-5′-uridyl) 4-(2,3,4,6-tetra-O-acetyl-β-d-glycopyranosyl)allophanates were obtained in the reactions of 2′,3′-O-isopropylidene-uridine and O-peracetylated β-d-gluco-, galacto- and xylopyranosylamines, and OCNCOCl. 2,3,4,6-Tetra-O-acetyl-β-d-glucopyranosyl isocyanate and N-(2′,3′-O-isopropylidene-5′-uridyl)urea gave 1-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-5-(2′,3′-O-isopropylidene-5′-uridyl)biuret. Deprotection of the β-d-gluco configured allophanate and biuret was carried out by standard methods. 相似文献
14.
Onyango M. Tedmann Stanley K. Madan Scott R.J. Oliver 《Inorganica chimica acta》2007,360(10):3408-3413
We report the synthesis and characterization of a seven coordinate europium complex, [EuCl3(C10H8N2O2) · 2CH3OH]. The growing interest in developing efficient light conversion molecular devices (LCMDs) necessitates the need for new fluorescent materials. Ideal physicochemical properties of the materials include ligand absorption, efficient metal to ligand transfer, and strong luminescence with a relatively long decay time. The design of such material requires distinct absorbing (ligand) and emitting (metal ion) components. While Eu3+ cation has a non-degenerate emitting level, 2,2′-bipyridine N,N dioxide is a heterocyclic ligand known to exhibit strong luminescence. Additional characterization is also described, including single crystal X-ray diffraction, IR and UV-Vis spectroscopies and elemental analysis. 相似文献
15.
The structures of the solvated iron(II) and iron(III) ions have been studied in solution and solid state by extended X-ray absorption fine structure (EXAFS) in three oxygen donor solvents, water, dimethylsulfoxide (Me2SO), N,N′-dimethylpropyleneurea (DMPU), and one sulfur donor solvent, N,N-dimethylthioformamide (DMTF); these solvents have different coordination and solvation properties. In addition, the structure of hexakis(dimethylsulfoxide)iron(III) perchlorate has been determined crystallographically to support the determination of the corresponding solvate in solution. The hydrated, the dimethylsulfoxide and N,N-dimethylthioformamide solvated iron(II) ions show regular octahedral coordination in both solution and solid state with mean Fe-O, Fe-O, and Fe-S bond distances of 2.10, 2.10, and 2.52 Å, respectively, whereas the N,N′-dimethylpropyleneurea iron(II) solvate is five-coordinated, d(Fe-O) = 2.06 Å. The compounds vary in color from light green (hydrate) to dark orange or red (DMPU). The hydrated iron(III) ion in aqueous solution and the dimethylsulfoxide solvated iron(III) ions in solution and solid state show the expected octahedral coordination, the Fe-O bond distances are 2.00 Å for both, whereas the N,N′-dimethylpropyleneurea iron(III) solvate is found to be five-coordinated with a mean Fe-O bond distance of 1.99 Å. The N,N-dimethylthioformamide solvated iron(III) ion in the solid perchlorate salt is tetrahedrally four-coordinated, the mean Fe-S bond distance is 2.20 Å. Iron(III) is reduced with time to iron(II) in N,N-dimethylthioformamide solution. The compounds vary in color from pale yellow (hydrate) to blackish red (DMPU). 相似文献
16.
Felix D. Sokolov Valery G. Shtyrlin Vasily V. Brusko Sergey V. Baranov Tadeusz Glowiak 《Inorganica chimica acta》2006,359(7):2087-2096
Thiourea, PhNHC(S)NHP(O)(OPri)2 (LH) chelates of CoII, NiII, and PdII ions have been obtained and investigated by single-crystal X-ray diffraction, UV, IR, NMR spectroscopy, and EI mass-spectrometry. The unusual 1,3-N,S-coordination via sulfur and NP(O) nitrogen atoms has been found in the trans-square-planar NiL2 and PdL2 complexes, whereas the 1,5-O,S-coordination is realized in the tetrahedral CoL2 complex. DFT calculations have revealed significant stabilization of the 1,3-N,S-structures due to stronger crystal field and the NH-OP hydrogen bonds. 相似文献
17.
Activation and induction of glycine N-methyltransferase by retinoids are tissue- and gender-specific
McMullen MH Rowling MJ Ozias MK Schalinske KL 《Archives of biochemistry and biophysics》2002,399(1):73-80
Betaine-homocysteine S-methyltransferase (BHMT; EC2.1.1.5) is a zinc metalloenzyme that catalyzes the transfer of a methyl group from betaine to homocysteine to produce dimethylglycine and Met, respectively. This enzyme is a member of a family of zinc-dependent methyltransferases that use thiols or selenols as methyl acceptors and which contain the following motif: G[ILV]NCX(20, 100)[ALV]X(2)[ILV]GGCCX(3)PX(2)I. We recently reported that the three cysteine residues within this motif function as ligands to zinc in BHMT because changing any of them to alanine abolished zinc-binding and enzyme activity (A. P. Breksa, III, and T. A. Garrow, 1999, Biochemistry 38, 13991-13998). To determine if other amino acid residues in this motif were critical for enzyme function, the two regions defined by the motif in human BHMT, GVNCH(218) and VRYIGGCCGFEPYHI(307), were subjected to semirandom and random site-directed mutagenesis. Mutant enzymes were classified as either active or inactive based on their ability to complement the Met auxotrophy of Escherichia coli strain J5-3. The Gly residue at position 214 was found to be absolutely essential for complementation. The positions occupied by Gly297, Gly298, and Gly301 favored substitutions of small amino acids like Ala and Ser. We hypothesize that these Gly residues provide the necessary flexibility to the Zn-binding region to permit coordination of the metal. 相似文献
18.
Elizabeth Ficko-Blean 《Journal of molecular biology》2009,390(2):208-6489
Many carbohydrate-active enzymes have complex architectures comprising multiple modules that may be involved in catalysis, carbohydrate binding, or protein-protein interactions. Carbohydrate-binding modules (CBMs) are a common ancillary module whose function is to promote the adherence of the complete enzyme to carbohydrate substrates. CBM family 32 has been proposed to be one of the most diverse CBM families classified to date, yet all of the structurally characterized CBM32s thus far recognize galactose-based ligands. Here, we report a unique binding specificity and mode of ligand binding for a family 32 CBM. NagHCBM32-2 is one of four CBM32 modules in NagH, a family 84 glycoside hydrolase secreted by Clostridium perfringens. NagHCBM32-2 has the β-sandwich scaffold common to members of the family; however, its specificity for N-acetylglucosamine is unusual among CBMs. X-ray crystallographic analysis of the module at resolutions from 1.45 to 2.0 Å and in complex with disaccharides reveals that its mode of sugar recognition is quite different from that observed for galactose-specific CBM32s. This study continues to unravel the diversity of CBMs found in family 32 and how these CBMs might impart the carbohydrate-binding specificity to the extracellular glycoside hydrolases in C. perfringens. 相似文献
19.
Ivan Campeotto Amanda H. Bolt Thomas A. Harman Caitriona Dennis Simon E.V. Phillips Arwen R. Pearson 《Journal of molecular biology》2010,404(1):56-69
The substrate specificity of Escherichia coli N-acetylneuraminic acid lyase was previously switched from the natural condensation of pyruvate with N-acetylmannosamine, yielding N-acetylneuraminic acid, to the aldol condensation generating N-alkylcarboxamide analogues of N-acetylneuraminic acid. This was achieved by a single mutation of Glu192 to Asn. In order to analyze the structural changes involved and to more fully understand the basis of this switch in specificity, we have isolated all 20 variants of the enzyme at position 192 and determined the activities with a range of substrates. We have also determined five high-resolution crystal structures: the structures of wild-type E. coli N-acetylneuraminic acid lyase in the presence and in the absence of pyruvate, the structures of the E192N variant in the presence and in the absence of pyruvate, and the structure of the E192N variant in the presence of pyruvate and a competitive inhibitor (2R,3R)-2,3,4-trihydroxy-N,N-dipropylbutanamide. All structures were solved in space group P21 at resolutions ranging from 1.65 Å to 2.2 Å. A comparison of these structures, in combination with the specificity profiles of the variants, reveals subtle differences that explain the details of the specificity changes. This work demonstrates the subtleties of enzyme-substrate interactions and the importance of determining the structures of enzymes produced by directed evolution, where the specificity determinants may change from one substrate to another. 相似文献
20.
A method is described for the identification of molecular species of acylphosphatidylglycerols containing a branched cyclo fatty acid ((S)-11-cycloheptyl-4-methylundecanoic acid; brc19:0) from Alicyclobacillus acidoterrestris and its identification as picolinyl ester by means of GC-MS. The combination of TLC, negative RP-HPLC-ESI-MS/MS, enzymatic hydrolysis, and GC-MS was used to identify unusual molecular species of acylphosphatidylglycerols with cyclic and branched FA. The acid, brc19:0, was also synthesized to unambiguously confirm its structure. According to feeding experiments with 13C-labeled propionate, the C3 internal unit (branched methyl) of brc19:0 is assembled from propionate and not from methionine. 相似文献